Directory UMM :Data Elmu:jurnal:S:Small Ruminant Research:Vol37.Issue1-2.Jul2000:
Small Ruminant Research 37 (2000) 99±107
Effect of parity on milk yield, composition, somatic cell count,
renneting parameters and bacteria counts of Comisana ewes
A. Sevia,*, L. Taibib, M. Albenzioa, A. Muscioa, G. Annicchiaricob
a
Istituto di Produzioni e Preparazioni Alimentari, FacoltaÁ di Agraria di Foggia, via Napoli, 25, 71100 Foggia, Italy
b
Istituto Sperimentale per la Zootecnia, via Napoli, 71020 Segezia-Foggia, Italy
Accepted 11 October 1999
Abstract
Twenty-four Comisana ewes, with no history of mastitis, were included in this study, with eight ewes each in parities 1, 2
and 3. Groups were separately penned on straw litter and ewes were individually checked for yield, composition, renneting
properties and bacteriological characteristics of milk from January, when separated from their lambs (50 3 days after
lambing), to May. Samples with more than 3.5 105 somatic cells/ml were cultured for mastitis related pathogens. Milk yield
was not signi®cantly affected by parity. The P3 ewes had signi®cantly higher milk protein, casein and fat contents compared to
the P1 and P2 ewes. The P3 ewes also had improved renneting ability of milk as compared to the P1 ewes. Quality of milk
decreased with lower lactations. The milk of P1 ewes had signi®cantly greater amounts of mesophilic bacteria than the P2 and
P3 ewes, as well as higher concentrations of psychrotrophs and total coliforms in their milk with respect to the P3 ewes.
Somatic cell counts in milk and the prevalence of subclinical mastitis were not changed by parity, although mastitis infection
set in progressively earlier as the number of lactations decreased. These results suggest that ewes in ®rst or second lactation
have a less favourable milk secretion status in relation to mastitis than ewes with a higher number of lactations. Milk yield and
quality of younger ewes may be improved by offering feed rations that take into account this reduced capacity to mobilise
body reserves. Also, most scrupulous control of sanitation of housing, equipment and personnel is necessary. # 2000 Elsevier
Science B.V. All rights reserved.
Keywords: Ewes; Parity; Milk yield; Mastitis; Milk composition
1. Introduction
Findings of several researchers on the effect of
parity on yield and quality of ewe milk are not
consistent. Casoli et al. (1989), Hatziminaoglou
*
Corresponding author. Tel.: 39-881-714544;
fax. 39-881-740211.
E-mail address: prodan.fgagr@isnet.it (A. Sevi)
et al. (1990) and Ubertalle et al. (1990) have observed
increased milk yields as the numbers of lactations
advanced, whereas Dell'Aquila et al., (1993) did not
®nd any signi®cant effect of parity on productive
levels of ewes.
A progressive increase of milk protein and fat
contents with increasing number of lactations has
been reported by Casoli et al. (1989) and Dell'Aquila
et al. (1993), but the opposite trend has been observed
0921-4488/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 9 2 1 - 4 4 8 8 ( 9 9 ) 0 0 1 3 3 - 9
100
A. Sevi et al. / Small Ruminant Research 37 (2000) 99±107
by Ubertalle (1989). Wohlt et al. (1981) did not ®nd
any in¯uence of parity on ewe milk constituents.
Con¯icting results may be due to other factors,
breed, feeding, number of lambs suckled, management practices and climatic conditions, which can
play a role when different parities are compared.
Differences between parities may also be due to
selection by breeders who allow only the best sheep
to be in the ¯ock for more than two lactations.
Little is known about the effect of parity on ewe
udder health. Bergonier et al. (1994) observed higher
somatic cell counts in sheep milk with the advancement of number of lactations. Sandrucci et al. (1992)
stated that higher SCC in older cows may be due to
increased amounts of epithelial cells in milk rather
than to higher leukocyte proportions (Wever and
Emanuelson, 1989). However, studies on electronic
microscopy of sheep milk state that there are just a few
epithelial cells in this milk (Lee and Outteridge, 1981;
Dulin et al., 1983).
The present study was undertaken to assess the
effects of parity on milk yield, composition, somatic
cell count, renneting parameters and bacteria counts of
Comisana ewes.
2. Materials and methods
2.1. Experimental animals
Twenty-four Comisana ewes, with no history of
mastitis, were used in this study, with eight ewes each
in parities 1, 2 and 3 (P1, P2 and P3, respectively). All
ewes lambed in mid-November and were separated
from their lambs at 50 3 days after parturition. The
animals were housed in a prefabricated building and
groups were separately penned on straw litter. Each
pen was provided with two mangers and a hay crib
(feeder space 0.45 m/animal). Ewes had free access
to automatic water troughs.
Groups were homogeneous in terms of number of
lambs suckled. At the commencement of the experiment, body weights were 51.19 2.62, 53.76 2.11
and 56.37 2.41 kg (means SE), respectively, in
the P1, P2 and P3 groups.
Ewes were fed a diet composed of pelletted concentrate, vetch/oat hay and oat straw (40, 50 and 10%
of total diet, respectively), which was offered as TMR
twice daily. The chemical composition of dry matter was
determined by the AOAC (1990) methods and resulted
in:15.4%crudeprotein,2.1%fat,byetherextract,23.4%
crude ®bre, 9.4% ash. Average daily DM intake was
2.36 0.28 kg per ewe during the study period.
2.2. Sampling and analyses of milk
Ewes were milked twice daily using pipeline milking machines (Alpha Laval Agri, SE-147 21 Tumbas,
Sweden). Daily milk yield was recorded by means of
graduated measuring cylinders attached to individual
milking units. Individual milk samples, consisting of
proportional volumes of morning and evening milk,
were taken after cleaning and disinfection of teats (0.7
alcohol) and discharging the ®rst streams of foremilk.
Samples were collected in 200 ml sterile plastic containers at fortnightly intervals through the lactation
period of 5 months (from January to May) and taken to
our laboratory under refrigeration. Upon arrival in the
laboratory (30±60 min after collection) and prior to
testing, milk samples were divided into two equal
portions, one half for milk composition, somatic cell
count and renneting parameter determination and the
other half for bacteriological analyses. The following
measurements were made: pH, total protein, fat and
lactose content, using an I.R. spectrophotometer
(Milko Scan 133B; Foss Electric, DK-3400 Hillerùd,
Denmark) according to the IDF (1990) standard;
casein content (IDF, 1964); somatic cell count
(SCC), using a Foss Electric Fossomatic 90 cell
counter (IDF, 1995); renneting parameters (clotting
time, rate of clot formation and clot ®rmness after
30 min) using a Foss Electric Formagraph and the
method of Zannoni and Annibaldi (1981); enumeration of mesophilic micro-organisms (IDF, 1991a),
psychrotrophs (IDF, 1991b), total coliforms (IDF,
1985) and faecal coliforms on Violet Red Bile Agar
(VRBA, I-20100 Biolife, Milan, Italy) incubated at
44.5 0.58C for 24 h.
At the beginning of the experiment and on the day
before each milk sampling, all the ewes were examined carefully to assess the absence of signs of clinical
mastitis, such as fever, pain or gland swelling. A small
quantity of milk was checked visually for signs of
mastitis. As proposed by Fruganti et al. (1985), an
aliquot of 0.01 ml from all milk samples containing
more than 3.5 105 somatic cells/ml was cultured for
A. Sevi et al. / Small Ruminant Research 37 (2000) 99±107
mastitis-related pathogens. Presumptive Escherichia
coli was detected after a 24 h incubation on VRBA
with MUG (4-methylumbelliferil-B-D-glucuronide)
(Hartman, 1989) at 44.5 0.58C. Staphylococci were
detected after a 24 h incubation on Mannitol Salt Agar
medium (Biolife) at 378C and subsequently identi®ed
to species level, using the API-STAPH system (Biomerieux, F-69280 Marcy l'Etoile, France). Streptococci were determined on modi®ed Edwards'
Aesculin medium (Oxoid, Basingstoke, RG24 09W,
United Kingdom) at 378C; streptococcal isolates were
then identi®ed to species level, using the API 20 Strep
System (Biomerieux). Pseudomonas spp. were determined using Pseudomonas Selective Agar (Oxoid);
Pseudomonas aeruginosa was detected after a 3-day
incubation on Pseudomonas agar F and Pseudomonas
Agar P (Oxoid) at 32±378C. As proposed by Watkins
et al. (1991), milk samples were recorded as bacteriologically positive when at least 1000 cfu of the same
type were isolated from 1 ml of milk. If two bacterial
species were isolated, they were treated as a case of
either species. If three or more bacterial species were
cultured from a sample, the sample was considered to
be contaminated (Fox et al., 1995). In addition, the
polymorphous neutrophil leucocyte (PMNL) count
was carried out according to the method proposed
by Morgante et al. (1996), which provides the direct
microscopic count of almost 100 cells in milk smears
stained with May±GruÈnwald Giemsa. As proposed by
Andrew et al. (1983), udders without clinical abnormalities and whose milk was apparently normal, with
somatic cell counts greater than 3.5 105, PMNL
counts higher than 20% of total somatic cells and
bacteriologically positive, were considered to have
subclinical mastitis when the same bacterial species
was isolated from milk samples at least in two of three
consecutive samplings.
The body weights of the ewes were recorded fortnightly anteprandium after the machine milking in the
morning.
At the end of May (196 3 days after parturition),
the ewes were moved from the experimental building
for mating and samplings were stopped.
2.3. Statistical analysis
Data from ewes considered to have subclinical
mastitis were excluded from statistical analysis. All
101
the variables were tested for normal distribution using
the Shapiro and Wilk (1965) test and milk somatic cell
and micro-organism counts were transformed into
logarithm form to normalize their frequency distributions before performing any statistical analysis. The
data were subjected to an analysis of variance, using
the GLM procedure of the SAS (1990) statistical
software (1990); the model used for all variables
was Y parity ewe (parity) month time of
sampling parity month parity month day
of sampling error, where Y is the milk yield data of
each individual ewe; ewe (parity) the error term to test
the effect of parity; month the effect of month through
lactation (1,. . ., 5); `day of sampling' the effect of day
for each month of lactation that milk data were
analysed (1, 2). For all parameters, model effects were
declared signi®cant at p < 0.05, unless otherwise stated.
3. Results and discussion
3.1. Milk yield and quality
Milk yield was not signi®cantly affected by parity
(Table 1), in agreement with previous reports (Dell'Aquila et al., 1993). Increased milk yields with the
advancement of number of lactations were found by
other groups (Casoli et al., 1989; Ubertalle et al., 1990;
Hatziminaoglou et al., 1990), whereas only a slight
increase of milk production was observed in this study
as the number of lactations advanced. However, when
milk samplings were stopped, ewes still had a milk
production greater than 1 kg/day. This would suggest
that had the study period been prolonged further the
slight differences found could have increased and
become signi®cant.
In contrast, parity strongly affected the quality of
ewes milk. Milk protein and casein contents increased
(p < 0.05) as the number of lactations advanced, with
the P3 ewes having higher protein and casein contents
in their milk as compared to the P2 (p < 0.05) and P1
ewes (p < 0.01). The P3 ewes also had a higher fat
content in their milk than P2 (p < 0.05), which in turn
had a higher milk fat content than P1 (p < 0.05). A
combined effect of parity month of lactation was
observed for milk protein (p 0.08) and fat content
(p 0.09), since differences among parities tended to
102
A. Sevi et al. / Small Ruminant Research 37 (2000) 99±107
Table 1
Least squares means of milk yield and composition of Comisana ewes in parities 1 (P1), 2 (P2) and 3 (P3)
Parities
SE
Level of significance
PT e
Mf
PT M
0.02
NS
**
NS
6.27a
5.77b
5.80b
5.99ab
6.15a
5.99a
0.03
*
**
NS
4.74ab
4.07c
4.21c
4.24c
4.68a
4.38b
4.92a
4.27b
4.41b
4.48b
4.77a
4.57a
0.02
*
**
NS
5.22c
4.68d
4.38d
5.34c
6.06b
5.13c
5.82b
5.06c
5.09c
5.81b
6.23d
5.60b
6.43ad
5.70be
5.48e
6.01ae
6.66a
6.05a
0.07
*
**
NS
5.50a
5.47a
5.55a
5.46a
5.38b
5.47a
5.35bc
5.37bc
5.40bc
5.29bc
5.39c
5.36ab
5.37bd
5.35cd
5.37bd
5.32bd
5.28d
5.33b
0.01
*
**
NS
P1
P2
P3
January
February
March
April
May
Mean
1.25b
1.54a
1.48a
1.47a
1.31b
1.41
1.31b
1.54a
1.52a
1.51a
1.32b
1.44
1.32b
1.59a
1.57a
1.56a
1.39b
1.48
January
February
March
April
May
Mean
5.72bc
5.43cd
5.31d
5.57c
5.92b
5.59b
5.90b
5.33d
5.48c
5.65c
6.03ab
5.68b
January
February
March
April
May
Mean
4.68b
4.11c
4.07c
4.19c
4.59ab
4.32b
January
February
March
April
May
Mean
January
February
March
April
May
Mean
Milk yield (kg/day)
Protein content (%)
Casein content (%)
Fat content (%)
Lactose content (%)
a,b,c,d
Means within the same rows or columns followed by different letters differ signi®cantly at p < 0.05.
Parity.
f
Month.
*
p < 0.05; ** p < 0.01.
e
decrease for both parameters as the lactation progressed.
Many possible causes could be suggested to explain
the increase in milk protein, casein and fat as the
number of lactations progressed. Firstly, the increased
body weight of the ewes with a greater number of
lactations which leads to a greater availability of body
reserves for the synthesis of milk components. This
hypothesis may be supported by the fact that the
differences between the groups which diminished in
late lactation when the contribution of body reserve to
milk component synthesis was reduced (Grummer,
1991). Secondly, the greater development of the udder
glandular tissue as the number of lactations rises could
103
A. Sevi et al. / Small Ruminant Research 37 (2000) 99±107
also result in an increased synthesis of milk constituents. Another possible explanation could be an
improved ef®ciency of the homeorhetic dynamics
involved in the partitioning of the nutrients for the
processes of lactogenesis and galactopoiesis as the
number of lactations increases (Hart, 1983). The
existence of a greater ¯ow of nutrients into galactopoiesis at the expense of other body tissues in older
than in younger ewes is supported by the fact that,
during the study period, average weight gains tended
to decrease (p 0.07) from the P1 to the P2 and the P3
group (118, 95 and 84 g/day, respectively).
Irrespective of parity, the contents of total protein,
casein and fat were higher in April and May, as a
consequence of reduced milk yield and increased de
novo synthesis of relatively more milk constituents
due to the positive energy balance of the ewes in late
lactation (Auldist et al., 1995).
The lactose content of milk decreased with increasing number of lactations and was signi®cantly higher
(p < 0.05) in the P1 than in the P3 group. Also, the
changes of lactose content in milk during the lactation were opposite to those observed for protein,
casein and fat contents, with the lowest lactose contents recorded during the last two months of the
lactation period.
These results, which are in line with those found by
other groups (Casoli et al., 1989) are not easy to
interpret given that lactose concentration in milk tends
to remain constant, at least in animals that are not
Table 2
Least squares means of renneting parameters of milk of Comisana ewes in parities 1 (P1), 2 (P2) and 3 (P3)
Parities
P1
SE
P2
P3
Level of significance
Parity
Month
Parity Month
pH
January
February
March
April
May
Mean
6.70
6.67
6.71
6.61
6.60
6.65
6.71
6.66
6.67
6.61
6.58
6.64
6.68
6.66
6.65
6.59
6.58
6.63
0.02
NS
NS
NS
January
February
March
April
May
Mean
22.0a
20.6bc
18.9c
20.5bc
19.4c
20.3
21.1a
20.5ab
18.0c
19.7abc
18.0c
19.5
20.4a
19.0ab
17.5c
18.7ab
17.4c
18.6
0.3
NS
**
NS
Rate of clot formation (min)
January
February
March
April
May
Mean
4.7a
4.6a
4.0ac
4.4a
3.9ac
4.3a
4.7a
4.4a
3.7bc
4.1abc
3.6bc
4.1ab
4.3a
4.0a
3.3b
3.9b
3.2b
3.7b
0.09
*
**
NS
39.6c
46.8bc
49.9b
45.4bc
46.7bc
45.7b
41.5c
46.3bc
52.1b
46.0bc
51.4abc
47.5ab
45.4c
51.0ac
58.0ab
49.1ac
55.2a
51.7a
1.23
*
*
NS
Clotting time (min)
Clot firmness (mm)
January
February
March
April
May
Mean
a,b,c
*
Means within the same rows or columns followed by different letters differ signi®cantly at p < 0.05.
p < 0.05; ** p < 0.01.
104
A. Sevi et al. / Small Ruminant Research 37 (2000) 99±107
The renneting behaviour of milk substantially
re¯ected the differences in milk casein and fat contents among parities as well as the variations of these
parameters through lactation (Table 2). Rate of clot
formation and clot ®rmness were improved (p < 0.01)
in the P3 as compared to the P1 group, whereas the P2
group exhibited intermediate values for both parameters. This could be expected, because clot forma-
suffering from mastitis, as lactose is the main osmotically active component in the milk. Pulina (1990)
interpreted this decline in milk lactose level as the
result of a worsening in udder health as the number of
lactations increased, but in this study at least this would
not seem to be the case. What is evident is the link with
fact that as the number of lactations advanced, the
endocrine±metabolic status in ewes changed.
Table 3
Somatic cell and bacteria count in milk of Comisana ewes in parities 1 (P1), 2 (P2) and 3 (P3)d
Parities
SE
P1
P2
P3
January
February
March
April
May
Mean
4.98
4.87
4.98
4.99
5.18
5.00
5.07
5.08
4.89
4.90
5.01
4.99
5.01
4.96
4.91
4.87
5.00
4.95
January
February
March
April
May
Mean
4.61b
4.51b
5.80a
5.46a
6.07a
5.29a
4.51bc
4.53bc
5.48ad
5.06ab
5.41d
4.99b
January
February
March
April
May
Mean
4.34c
5.07a
5.48a
5.51a
5.46a
5.17a
January
February
March
April
May
Mean
January
February
March
April
May
Mean
Level of significance
Parity
Month
Parity Month
0.07
NS
NS
NS
4.58bc
4.41bc
5.49a
4.47b
5.21ad
4.83b
0.06
*
**
NS
4.33c
5.07a
5.11a
5.51ab
5.07ab
5.01ab
4.49bc
4.78bc
5.11bc
5.02b
4.77b
4.83b
0.05
*
**
NS
3.34c
3.35c
3.97ac
4.01a
4.42a
3.81a
3.19c
3.53bc
3.70bc
3.66abc
3.80b
3.57ab
3.15bc
3.39bc
3.55bc
3.37b
3.54b
3.40b
0.08
*
*
NS
0.21
1.01
1.05
1.79
2.38
1.28
0.52
0.88
0.80
1.33
2.11
1.12
0.40
0.84
0.48
1.06
1.94
0.94
0.12
NS
NS
NS
Somatic cell count
Mesophile count
Psychrotroph count
Total coliform count
Faecal coliform count
a,b,c
Means within the same rows or columns followed by different letters differ signi®cantly at p < 0.05.
Data are least square means of log 10 of smoatic cells and cfu x ml of milk.
*
p < 0.05; ** p < 0.01.
d
105
A. Sevi et al. / Small Ruminant Research 37 (2000) 99±107
tion involves the aggregation of casein micelles into a
network within which the fat is entrapped (Dalgleish,
1993).
Also, pH and clotting time were ameliorated by the
increasing number of lactations, but differences
among groups were smaller and not signi®cant for
these parameters.
The somatic cell count (SCC) in milk was not
changed by parity (Table 3). Average values were
acceptably low, ranging from 249 to 321 103
somatic cell/ml of milk in parities 3 and 1, respectively. Irrespective of parity, the highest values were
recorded in May and the lowest in February (671 and
203 103 somatic cell/ml of milk on average, respectively). SCC were higher than those found by Morgante et al. (1996) in Comisana ewes.
Conversely, the analysis of variance of the logarithmic values highlighted a marked effect of number
of lactations on milk bacteria counts. The P1 ewes
exhibited signi®cantly greater (p < 0.05) amounts of
mesophilic bacteria than the P2 and P3 ewes (521 vs.
348 and 298 103 cfu/ml, respectively) as well as
higher concentrations of psychrotrophs and total coliforms in their milk with respect to the P3 ewes (377 vs.
163 103 cfu/ml and 19 vs. 7 103 cfu/ml, respectively). Although the P1 ewes had a higher microorganism concentration in this milk, but there was no
increase in milk SCC. This could suggest that the
greater bacterial colonisation of the udder in these
ewes could be attributed to a reduced ef®ciency in the
natural defence mechanisms against the penetration
and multiplication of bacteria in the udder (Varner and
Johnson, 1983).
Increased concentrations of micro-organisms could
play a role in protein and fat contents decrease in the
milk yield of the P1 ewes, due to enhanced postsecretory lipolytic and proteolytic actions in milk by
enzymes produced from the bacterial ¯ora (Higoshi and
Hamada, 1975; Auldist et al., 1996; Sevi et al., 1999).
3.2. Incidence of subclinical mastitis
There were no cases of clinical mastitis during the
study period. One case of subclinical mastitis (Table 4)
was recorded in each group, but mastitis infection set
in progressively earlier as the number of lactations
decreased and this supports the hypothesis of less
ef®cient natural defence mechanisms in younger ewes,
Table 4
Cases of subclinical mastitis, bacteriologically positive milk
samples and bacteria isolated from milk of Comisana ewes in
parities 1 (P1), 2 (P2) and 3 (P3)
Parities
P1
P2
P3
January
February
March
April
May
0
1
1
1
1
0
0
1
1
1
0
0
0
1
1
Bacteriologically positive milk samples
January
February
March
April
May
2
2
5
3
3
1
1
3
4
2
1
2
1
3
2
Cases of subclinical mastitis
Bacteria isolated and number of milk samples from which isolated
Escherichia coli
6
4
4
Pseudomonas spp.
2
2
2
Pseudomonas aeruginosa
2
1
1
Staphylococcus aureus
2
1
0
Staphylococcus xylosus
0
1
1
Staphylococcus hyicus
1
0
0
Other CN-staphylococci
3
3
1
Streptococcus agalactiae
0
0
0
Streptococcus pneumoniae
1
1
0
Enterococcus spp.
6
6
3
Other streptococci
3
2
2
perhaps due to a less advanced development of the
immune system or to greater susceptibility to environmental stress (Bertoni, 1996). Exposure to bacteria
is a prerequisite but the development of infection and
mastitis is a balance between the natural defence
mechanisms of the teat and mammary gland and
the number and pathogenicity of the micro-organisms
in contact with the entrance of the teat canal (Klastrup
et al., 1987).
As a consequence, the number of bacteriologically
positive milk samples was higher in the P1 group
(n 15) than in the P2 (n 11) and P3 groups
(n 9). On the whole, bacteria or combinations of
bacteria were isolated from 35 milk samples and
environmental bacteria were largely predominant.
Streptococci (especially Enterococcus spp.) constituted the majority of bacteria isolated, since they were
isolated from about 70% of the 35 bacteriologically
106
A. Sevi et al. / Small Ruminant Research 37 (2000) 99±107
positive milk samples. E. coli, coagulase-negative
(CN)-staphylococci and Pseudomonas spp. were isolated from 14, 10 and 6 milk samples at 40, 29, 17%,
respectively. S. aureus and P. aeruginosa were detected
in four and three milk samples, respectively, whereas S.
agalactiae was not isolated from any milk sample.
4. Conclusions
Ewes milk yield was not changed by parity, but milk
protein, casein and fat contents increased and renneting ability of milk improved as the number of lactations advanced. Somatic cell counts in milk were very
similar in parities 1, 2 and 3 and groups had one case
of subclinical mastitis each. However, bacteria counts
in milk increased and mastitis infection set in progressively earlier with lower numbers of lactations.
Further studies on this topic are required using
larger ¯ocks. Nevertheless, our ®ndings indicate that
the differences in milk composition linked to the
number of lactations may depend on different endocrine and metabolic status in ewes of varying ages.
Also, most scrupulous control of sanitation of housing,
equipment and personnel is necessary.
References
Andrew, R.J., Kitchen, B.J., Kwee, W.S., Duncalfe, F., 1983.
Relationship between individual cow somatic cell count and the
mastitis infection status of the udder. Aust. J. Dairy Technol.
38, 71±74.
AOAC, 1990. Of®cial Methods of Analysis, 15th ed. Association of
Of®cial Analytical Chemists, Washington, DC, pp. 69±88.
Auldist, M.J., Coats, S., Rogers, G.L., McDowell, G.H., 1995.
Changes in the composition of milk from healthy and mastitic
dairy cows during the lactation cycle. Austr. J. Exper. Agric. 35,
427±436.
Auldist, M.J., Coats, S., Sutherlans, B.J., Mayes, J.J., McDowell,
G.H., Rogers, G.L., 1996. Effects of somatic cell count and
stage of lactation on raw milk composition and the yield and
quality of cheddar cheese. J. Dairy Res. 63, 269±280.
Bergonier, D., Van de Wiele, A., Arranz, J.M., Barillet, F.,
Lagriffoul, G., Concordet, G., Berthelot, X., 1994. Noninfectious factors affecting somatic cell count in dairy sheep
and goat. In: Rubino, R. (Ed.), Somatic Cells and Milk Quality
in Small Ruminants, pp. 139±167.
Bertoni, G., 1996. Environment feeding and milk quality.
Informatore Agrario (Suppl.) 52, 5±41.
Casoli, C., Duranti, E., Morbidini, L., Panella, F., Vizioli, V., 1989.
Quantitative and compositional variations of Massases sheep
milk by parity and stage of lactation. Small Rumin. Res. 2,
47±62.
Dalgleish, D.G., 1993. Bovine milk protein properties and the
manufacturing quality of milk. Livst. Prod. Sci. 35, 75±93.
Dell'Aquila, S., Pilla, A.M., Catillo, G., Scardella, G., Taibi, L.,
1993. Milk yield of Comisana, Delle Langhe, Massese, Sarda
and crossbred ewes. Zootecnica Nutrizione Animale 14, 95±102.
Dulin, A.M., Paape, M.J., Berkow, S., Hamosh, M., Hamosh, P.,
1983. Comparison of total somatic cells and differential cellular
composition in milk from cows, sheep, goats and humans.
Federation Proceedings 42, 1331.
Fox, L.K., Chester, S.T., Hallberg, J.W., Nickerson, J.W., Pankey,
J.W., Weawer, L.D., 1995. Survey of intramammary infections
in dairy heifers at breeding age and ®rst parturition. J. Dairy
Sci. 78, 1619±1628.
Fruganti, G.S., Ranucci, S., Tesei, B., Valente, C., 1985.
Assessment of the health status of ewes udder throughout
lactation. Clinica Veterinaria 108, 286±296.
Grummer, R.R., 1991. Effect of feeding on the composition of milk
fat. J. Dairy Sci. 74, 3244±3257.
Hart, I.C., 1983. Endocrine control of nutrient partition in lactating
ruminants. Proc. Nutr. Soc. 42, 181±194.
Hartman, P.A., 1989. The MUG (gluconidase) test for Escherichia
coli in feed and water. In: Balows, A., Tilton, R.C., Turano, A.
(Eds.), Rapid Methods and Automation in Microbiology and
Immunology, Brixion Academic Press, Brescia, Italy, pp. 290±
308.
Hatziminaoglou, I., Geogordiudis, A., Karalazos, A., 1990. Factors
affecting milk yield and proli®cacy of Karagouniko sheep in
West Thessaly (Greece). Livst. Prod. Sci. 24, 181±186.
Higoshi, H., Hamada, S., 1975. Proteolytic and lipolytic activities
of psychrotrophic bacteria originated from raw milk. J. Food
Hyg. Soc. Japan 17, 1±47.
IDF, 1964. Determination of the casein content of milk. IDF
Standard No. 29. International Dairy Federation, Brussels,
Belgium.
IDF, 1985. Enumeration of coliforms. IDF Standard No. 73A.
International Dairy Federation, Brussels, Belgium.
IDF, 1990. Determination of milk fat, protein and lactose content
Ð Guide for the operation of mid-infra-red instruments. IDF
Standard No. 141B. International Dairy Federation, Brussels,
Belgium.
IDF, 1991a. Enumeration of micro-organisms Ð Colony count at
308C. IDF Standard No. 100B. International Dairy Federation,
Brussels, Belgium.
IDF, 1991b. Enumeration of psychrotrophic micro-organisms Ð
Colony count at 6.58C. IDF Standard No. 101A. International
Dairy Federation, Brussels, Belgium.
IDF, 1995. Enumeration of somatic cells. IDF Standard No. 148A.
International Dairy Federation, Brussels, Belgium.
Klastrup, O., Bakken, G., Bramley, J., Bushnell, R., 1987.
Environmental in¯uences on bovine mastitis. Bulletin No.
217. International Dairy Federation, Brussels, Belgium.
Lee, C.S., Outteridge, P.M., 1981. Leucocytes of sheep colostrum,
milk and involution secretion, with particular reference to
ultrastructure and lymphocyte sub-popolations. J. Dairy Res.
48, 225±237.
A. Sevi et al. / Small Ruminant Research 37 (2000) 99±107
Morgante, M., Ranucci, S., Pauselli, M., Casoli, C., Duranti, E.,
1996. Total and differential cell count in milk of primiparous
Comisana ewes without clinical signs of mastitis. Small Rumin.
Res. 21, 265±271.
Pulina, G., 1990. In¯uence of feeding on ewes milk quality.
Informatore Agrario 37, 31±39.
Sandrucci, A., Tamburini, A., Rapetti, L., 1992. A study on the use
of a linear score for the evaluation of milk somatic cell count.
Proceedings of the 27th Simposio Internazionale di Zootecnia,
SocietaÁ per il Progresso della Zootecnia, Milan, Italy, pp. 175±190.
SAS, 1990 SAS/STAT User's Guide Version 6, 4th ed., Statistical
Analysis System Inst, Cary, NC.
Sevi, A., Massa, S., Annicchiarico, G., Dell'Aquila, S., Muscio, A.,
1999. Effect of stocking density on ewes milk yield, udder
health and micro-environment. J. Dairy Res., in press.
Shapiro, S.S., Wilk, M., 1965. An analysis of variance test for
normality. Biometrika 52, 591±601.
Ubertalle, A., 1989. Factors affecting the quality of ewes milk.
Proceedings of The Accademia Economico-agraria dei Georgo®li, Stamperia Editoriale Parenti, Firenze, Italy, pp. 1±18.
107
Ubertalle, A., Bianchi, M., Errante, J., Battaglini, L.M., 1990.
Proli®cacy and milk yield: phenotypic relationships in Delle
Langhe ewes. Zootecnica Nutrizione Animale 16, 219±224.
Varner, M.A., Johnson, B.H., 1983. In¯uence of adrenocorticotropin upon milk production, milk constituents, and endocrine
measures of dairy cows. J. Dairy Sci. 66, 458±465.
Watkins, G.H., Burriel, A.R., Jones, J.E.T., 1991. A ®eld
investigation of subclinical mastitis in sheep in Southern
England. Br. Vet. J. 147, 413±420.
Wever, P., Emanuelson, U., 1989. Effects of systematic in¯uences
and intramammary infection on differential and total somatic
cell counts in quarter milk samples from dairy cows. Acta Vet.
Scandin. 30, 465±474.
Wohlt, J.E., Kleyn, D.H., Vandernoot, G.W., Selfridge, D.J.,
Novotney, C.A., 1981. Effect of stage of lactation, age of
ewe, sibling status and sex of lamb on gross and minor
constituents of Dorset ewe milk. J. Dairy Sci. 64, 2175±2184.
Zannoni, M., Annibaldi, S., 1981. Standardisation of the renneting
ability of milk by Formagraph. Scienza e Tecnica LattieroCasearia 32, 9±94.
Effect of parity on milk yield, composition, somatic cell count,
renneting parameters and bacteria counts of Comisana ewes
A. Sevia,*, L. Taibib, M. Albenzioa, A. Muscioa, G. Annicchiaricob
a
Istituto di Produzioni e Preparazioni Alimentari, FacoltaÁ di Agraria di Foggia, via Napoli, 25, 71100 Foggia, Italy
b
Istituto Sperimentale per la Zootecnia, via Napoli, 71020 Segezia-Foggia, Italy
Accepted 11 October 1999
Abstract
Twenty-four Comisana ewes, with no history of mastitis, were included in this study, with eight ewes each in parities 1, 2
and 3. Groups were separately penned on straw litter and ewes were individually checked for yield, composition, renneting
properties and bacteriological characteristics of milk from January, when separated from their lambs (50 3 days after
lambing), to May. Samples with more than 3.5 105 somatic cells/ml were cultured for mastitis related pathogens. Milk yield
was not signi®cantly affected by parity. The P3 ewes had signi®cantly higher milk protein, casein and fat contents compared to
the P1 and P2 ewes. The P3 ewes also had improved renneting ability of milk as compared to the P1 ewes. Quality of milk
decreased with lower lactations. The milk of P1 ewes had signi®cantly greater amounts of mesophilic bacteria than the P2 and
P3 ewes, as well as higher concentrations of psychrotrophs and total coliforms in their milk with respect to the P3 ewes.
Somatic cell counts in milk and the prevalence of subclinical mastitis were not changed by parity, although mastitis infection
set in progressively earlier as the number of lactations decreased. These results suggest that ewes in ®rst or second lactation
have a less favourable milk secretion status in relation to mastitis than ewes with a higher number of lactations. Milk yield and
quality of younger ewes may be improved by offering feed rations that take into account this reduced capacity to mobilise
body reserves. Also, most scrupulous control of sanitation of housing, equipment and personnel is necessary. # 2000 Elsevier
Science B.V. All rights reserved.
Keywords: Ewes; Parity; Milk yield; Mastitis; Milk composition
1. Introduction
Findings of several researchers on the effect of
parity on yield and quality of ewe milk are not
consistent. Casoli et al. (1989), Hatziminaoglou
*
Corresponding author. Tel.: 39-881-714544;
fax. 39-881-740211.
E-mail address: prodan.fgagr@isnet.it (A. Sevi)
et al. (1990) and Ubertalle et al. (1990) have observed
increased milk yields as the numbers of lactations
advanced, whereas Dell'Aquila et al., (1993) did not
®nd any signi®cant effect of parity on productive
levels of ewes.
A progressive increase of milk protein and fat
contents with increasing number of lactations has
been reported by Casoli et al. (1989) and Dell'Aquila
et al. (1993), but the opposite trend has been observed
0921-4488/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 9 2 1 - 4 4 8 8 ( 9 9 ) 0 0 1 3 3 - 9
100
A. Sevi et al. / Small Ruminant Research 37 (2000) 99±107
by Ubertalle (1989). Wohlt et al. (1981) did not ®nd
any in¯uence of parity on ewe milk constituents.
Con¯icting results may be due to other factors,
breed, feeding, number of lambs suckled, management practices and climatic conditions, which can
play a role when different parities are compared.
Differences between parities may also be due to
selection by breeders who allow only the best sheep
to be in the ¯ock for more than two lactations.
Little is known about the effect of parity on ewe
udder health. Bergonier et al. (1994) observed higher
somatic cell counts in sheep milk with the advancement of number of lactations. Sandrucci et al. (1992)
stated that higher SCC in older cows may be due to
increased amounts of epithelial cells in milk rather
than to higher leukocyte proportions (Wever and
Emanuelson, 1989). However, studies on electronic
microscopy of sheep milk state that there are just a few
epithelial cells in this milk (Lee and Outteridge, 1981;
Dulin et al., 1983).
The present study was undertaken to assess the
effects of parity on milk yield, composition, somatic
cell count, renneting parameters and bacteria counts of
Comisana ewes.
2. Materials and methods
2.1. Experimental animals
Twenty-four Comisana ewes, with no history of
mastitis, were used in this study, with eight ewes each
in parities 1, 2 and 3 (P1, P2 and P3, respectively). All
ewes lambed in mid-November and were separated
from their lambs at 50 3 days after parturition. The
animals were housed in a prefabricated building and
groups were separately penned on straw litter. Each
pen was provided with two mangers and a hay crib
(feeder space 0.45 m/animal). Ewes had free access
to automatic water troughs.
Groups were homogeneous in terms of number of
lambs suckled. At the commencement of the experiment, body weights were 51.19 2.62, 53.76 2.11
and 56.37 2.41 kg (means SE), respectively, in
the P1, P2 and P3 groups.
Ewes were fed a diet composed of pelletted concentrate, vetch/oat hay and oat straw (40, 50 and 10%
of total diet, respectively), which was offered as TMR
twice daily. The chemical composition of dry matter was
determined by the AOAC (1990) methods and resulted
in:15.4%crudeprotein,2.1%fat,byetherextract,23.4%
crude ®bre, 9.4% ash. Average daily DM intake was
2.36 0.28 kg per ewe during the study period.
2.2. Sampling and analyses of milk
Ewes were milked twice daily using pipeline milking machines (Alpha Laval Agri, SE-147 21 Tumbas,
Sweden). Daily milk yield was recorded by means of
graduated measuring cylinders attached to individual
milking units. Individual milk samples, consisting of
proportional volumes of morning and evening milk,
were taken after cleaning and disinfection of teats (0.7
alcohol) and discharging the ®rst streams of foremilk.
Samples were collected in 200 ml sterile plastic containers at fortnightly intervals through the lactation
period of 5 months (from January to May) and taken to
our laboratory under refrigeration. Upon arrival in the
laboratory (30±60 min after collection) and prior to
testing, milk samples were divided into two equal
portions, one half for milk composition, somatic cell
count and renneting parameter determination and the
other half for bacteriological analyses. The following
measurements were made: pH, total protein, fat and
lactose content, using an I.R. spectrophotometer
(Milko Scan 133B; Foss Electric, DK-3400 Hillerùd,
Denmark) according to the IDF (1990) standard;
casein content (IDF, 1964); somatic cell count
(SCC), using a Foss Electric Fossomatic 90 cell
counter (IDF, 1995); renneting parameters (clotting
time, rate of clot formation and clot ®rmness after
30 min) using a Foss Electric Formagraph and the
method of Zannoni and Annibaldi (1981); enumeration of mesophilic micro-organisms (IDF, 1991a),
psychrotrophs (IDF, 1991b), total coliforms (IDF,
1985) and faecal coliforms on Violet Red Bile Agar
(VRBA, I-20100 Biolife, Milan, Italy) incubated at
44.5 0.58C for 24 h.
At the beginning of the experiment and on the day
before each milk sampling, all the ewes were examined carefully to assess the absence of signs of clinical
mastitis, such as fever, pain or gland swelling. A small
quantity of milk was checked visually for signs of
mastitis. As proposed by Fruganti et al. (1985), an
aliquot of 0.01 ml from all milk samples containing
more than 3.5 105 somatic cells/ml was cultured for
A. Sevi et al. / Small Ruminant Research 37 (2000) 99±107
mastitis-related pathogens. Presumptive Escherichia
coli was detected after a 24 h incubation on VRBA
with MUG (4-methylumbelliferil-B-D-glucuronide)
(Hartman, 1989) at 44.5 0.58C. Staphylococci were
detected after a 24 h incubation on Mannitol Salt Agar
medium (Biolife) at 378C and subsequently identi®ed
to species level, using the API-STAPH system (Biomerieux, F-69280 Marcy l'Etoile, France). Streptococci were determined on modi®ed Edwards'
Aesculin medium (Oxoid, Basingstoke, RG24 09W,
United Kingdom) at 378C; streptococcal isolates were
then identi®ed to species level, using the API 20 Strep
System (Biomerieux). Pseudomonas spp. were determined using Pseudomonas Selective Agar (Oxoid);
Pseudomonas aeruginosa was detected after a 3-day
incubation on Pseudomonas agar F and Pseudomonas
Agar P (Oxoid) at 32±378C. As proposed by Watkins
et al. (1991), milk samples were recorded as bacteriologically positive when at least 1000 cfu of the same
type were isolated from 1 ml of milk. If two bacterial
species were isolated, they were treated as a case of
either species. If three or more bacterial species were
cultured from a sample, the sample was considered to
be contaminated (Fox et al., 1995). In addition, the
polymorphous neutrophil leucocyte (PMNL) count
was carried out according to the method proposed
by Morgante et al. (1996), which provides the direct
microscopic count of almost 100 cells in milk smears
stained with May±GruÈnwald Giemsa. As proposed by
Andrew et al. (1983), udders without clinical abnormalities and whose milk was apparently normal, with
somatic cell counts greater than 3.5 105, PMNL
counts higher than 20% of total somatic cells and
bacteriologically positive, were considered to have
subclinical mastitis when the same bacterial species
was isolated from milk samples at least in two of three
consecutive samplings.
The body weights of the ewes were recorded fortnightly anteprandium after the machine milking in the
morning.
At the end of May (196 3 days after parturition),
the ewes were moved from the experimental building
for mating and samplings were stopped.
2.3. Statistical analysis
Data from ewes considered to have subclinical
mastitis were excluded from statistical analysis. All
101
the variables were tested for normal distribution using
the Shapiro and Wilk (1965) test and milk somatic cell
and micro-organism counts were transformed into
logarithm form to normalize their frequency distributions before performing any statistical analysis. The
data were subjected to an analysis of variance, using
the GLM procedure of the SAS (1990) statistical
software (1990); the model used for all variables
was Y parity ewe (parity) month time of
sampling parity month parity month day
of sampling error, where Y is the milk yield data of
each individual ewe; ewe (parity) the error term to test
the effect of parity; month the effect of month through
lactation (1,. . ., 5); `day of sampling' the effect of day
for each month of lactation that milk data were
analysed (1, 2). For all parameters, model effects were
declared signi®cant at p < 0.05, unless otherwise stated.
3. Results and discussion
3.1. Milk yield and quality
Milk yield was not signi®cantly affected by parity
(Table 1), in agreement with previous reports (Dell'Aquila et al., 1993). Increased milk yields with the
advancement of number of lactations were found by
other groups (Casoli et al., 1989; Ubertalle et al., 1990;
Hatziminaoglou et al., 1990), whereas only a slight
increase of milk production was observed in this study
as the number of lactations advanced. However, when
milk samplings were stopped, ewes still had a milk
production greater than 1 kg/day. This would suggest
that had the study period been prolonged further the
slight differences found could have increased and
become signi®cant.
In contrast, parity strongly affected the quality of
ewes milk. Milk protein and casein contents increased
(p < 0.05) as the number of lactations advanced, with
the P3 ewes having higher protein and casein contents
in their milk as compared to the P2 (p < 0.05) and P1
ewes (p < 0.01). The P3 ewes also had a higher fat
content in their milk than P2 (p < 0.05), which in turn
had a higher milk fat content than P1 (p < 0.05). A
combined effect of parity month of lactation was
observed for milk protein (p 0.08) and fat content
(p 0.09), since differences among parities tended to
102
A. Sevi et al. / Small Ruminant Research 37 (2000) 99±107
Table 1
Least squares means of milk yield and composition of Comisana ewes in parities 1 (P1), 2 (P2) and 3 (P3)
Parities
SE
Level of significance
PT e
Mf
PT M
0.02
NS
**
NS
6.27a
5.77b
5.80b
5.99ab
6.15a
5.99a
0.03
*
**
NS
4.74ab
4.07c
4.21c
4.24c
4.68a
4.38b
4.92a
4.27b
4.41b
4.48b
4.77a
4.57a
0.02
*
**
NS
5.22c
4.68d
4.38d
5.34c
6.06b
5.13c
5.82b
5.06c
5.09c
5.81b
6.23d
5.60b
6.43ad
5.70be
5.48e
6.01ae
6.66a
6.05a
0.07
*
**
NS
5.50a
5.47a
5.55a
5.46a
5.38b
5.47a
5.35bc
5.37bc
5.40bc
5.29bc
5.39c
5.36ab
5.37bd
5.35cd
5.37bd
5.32bd
5.28d
5.33b
0.01
*
**
NS
P1
P2
P3
January
February
March
April
May
Mean
1.25b
1.54a
1.48a
1.47a
1.31b
1.41
1.31b
1.54a
1.52a
1.51a
1.32b
1.44
1.32b
1.59a
1.57a
1.56a
1.39b
1.48
January
February
March
April
May
Mean
5.72bc
5.43cd
5.31d
5.57c
5.92b
5.59b
5.90b
5.33d
5.48c
5.65c
6.03ab
5.68b
January
February
March
April
May
Mean
4.68b
4.11c
4.07c
4.19c
4.59ab
4.32b
January
February
March
April
May
Mean
January
February
March
April
May
Mean
Milk yield (kg/day)
Protein content (%)
Casein content (%)
Fat content (%)
Lactose content (%)
a,b,c,d
Means within the same rows or columns followed by different letters differ signi®cantly at p < 0.05.
Parity.
f
Month.
*
p < 0.05; ** p < 0.01.
e
decrease for both parameters as the lactation progressed.
Many possible causes could be suggested to explain
the increase in milk protein, casein and fat as the
number of lactations progressed. Firstly, the increased
body weight of the ewes with a greater number of
lactations which leads to a greater availability of body
reserves for the synthesis of milk components. This
hypothesis may be supported by the fact that the
differences between the groups which diminished in
late lactation when the contribution of body reserve to
milk component synthesis was reduced (Grummer,
1991). Secondly, the greater development of the udder
glandular tissue as the number of lactations rises could
103
A. Sevi et al. / Small Ruminant Research 37 (2000) 99±107
also result in an increased synthesis of milk constituents. Another possible explanation could be an
improved ef®ciency of the homeorhetic dynamics
involved in the partitioning of the nutrients for the
processes of lactogenesis and galactopoiesis as the
number of lactations increases (Hart, 1983). The
existence of a greater ¯ow of nutrients into galactopoiesis at the expense of other body tissues in older
than in younger ewes is supported by the fact that,
during the study period, average weight gains tended
to decrease (p 0.07) from the P1 to the P2 and the P3
group (118, 95 and 84 g/day, respectively).
Irrespective of parity, the contents of total protein,
casein and fat were higher in April and May, as a
consequence of reduced milk yield and increased de
novo synthesis of relatively more milk constituents
due to the positive energy balance of the ewes in late
lactation (Auldist et al., 1995).
The lactose content of milk decreased with increasing number of lactations and was signi®cantly higher
(p < 0.05) in the P1 than in the P3 group. Also, the
changes of lactose content in milk during the lactation were opposite to those observed for protein,
casein and fat contents, with the lowest lactose contents recorded during the last two months of the
lactation period.
These results, which are in line with those found by
other groups (Casoli et al., 1989) are not easy to
interpret given that lactose concentration in milk tends
to remain constant, at least in animals that are not
Table 2
Least squares means of renneting parameters of milk of Comisana ewes in parities 1 (P1), 2 (P2) and 3 (P3)
Parities
P1
SE
P2
P3
Level of significance
Parity
Month
Parity Month
pH
January
February
March
April
May
Mean
6.70
6.67
6.71
6.61
6.60
6.65
6.71
6.66
6.67
6.61
6.58
6.64
6.68
6.66
6.65
6.59
6.58
6.63
0.02
NS
NS
NS
January
February
March
April
May
Mean
22.0a
20.6bc
18.9c
20.5bc
19.4c
20.3
21.1a
20.5ab
18.0c
19.7abc
18.0c
19.5
20.4a
19.0ab
17.5c
18.7ab
17.4c
18.6
0.3
NS
**
NS
Rate of clot formation (min)
January
February
March
April
May
Mean
4.7a
4.6a
4.0ac
4.4a
3.9ac
4.3a
4.7a
4.4a
3.7bc
4.1abc
3.6bc
4.1ab
4.3a
4.0a
3.3b
3.9b
3.2b
3.7b
0.09
*
**
NS
39.6c
46.8bc
49.9b
45.4bc
46.7bc
45.7b
41.5c
46.3bc
52.1b
46.0bc
51.4abc
47.5ab
45.4c
51.0ac
58.0ab
49.1ac
55.2a
51.7a
1.23
*
*
NS
Clotting time (min)
Clot firmness (mm)
January
February
March
April
May
Mean
a,b,c
*
Means within the same rows or columns followed by different letters differ signi®cantly at p < 0.05.
p < 0.05; ** p < 0.01.
104
A. Sevi et al. / Small Ruminant Research 37 (2000) 99±107
The renneting behaviour of milk substantially
re¯ected the differences in milk casein and fat contents among parities as well as the variations of these
parameters through lactation (Table 2). Rate of clot
formation and clot ®rmness were improved (p < 0.01)
in the P3 as compared to the P1 group, whereas the P2
group exhibited intermediate values for both parameters. This could be expected, because clot forma-
suffering from mastitis, as lactose is the main osmotically active component in the milk. Pulina (1990)
interpreted this decline in milk lactose level as the
result of a worsening in udder health as the number of
lactations increased, but in this study at least this would
not seem to be the case. What is evident is the link with
fact that as the number of lactations advanced, the
endocrine±metabolic status in ewes changed.
Table 3
Somatic cell and bacteria count in milk of Comisana ewes in parities 1 (P1), 2 (P2) and 3 (P3)d
Parities
SE
P1
P2
P3
January
February
March
April
May
Mean
4.98
4.87
4.98
4.99
5.18
5.00
5.07
5.08
4.89
4.90
5.01
4.99
5.01
4.96
4.91
4.87
5.00
4.95
January
February
March
April
May
Mean
4.61b
4.51b
5.80a
5.46a
6.07a
5.29a
4.51bc
4.53bc
5.48ad
5.06ab
5.41d
4.99b
January
February
March
April
May
Mean
4.34c
5.07a
5.48a
5.51a
5.46a
5.17a
January
February
March
April
May
Mean
January
February
March
April
May
Mean
Level of significance
Parity
Month
Parity Month
0.07
NS
NS
NS
4.58bc
4.41bc
5.49a
4.47b
5.21ad
4.83b
0.06
*
**
NS
4.33c
5.07a
5.11a
5.51ab
5.07ab
5.01ab
4.49bc
4.78bc
5.11bc
5.02b
4.77b
4.83b
0.05
*
**
NS
3.34c
3.35c
3.97ac
4.01a
4.42a
3.81a
3.19c
3.53bc
3.70bc
3.66abc
3.80b
3.57ab
3.15bc
3.39bc
3.55bc
3.37b
3.54b
3.40b
0.08
*
*
NS
0.21
1.01
1.05
1.79
2.38
1.28
0.52
0.88
0.80
1.33
2.11
1.12
0.40
0.84
0.48
1.06
1.94
0.94
0.12
NS
NS
NS
Somatic cell count
Mesophile count
Psychrotroph count
Total coliform count
Faecal coliform count
a,b,c
Means within the same rows or columns followed by different letters differ signi®cantly at p < 0.05.
Data are least square means of log 10 of smoatic cells and cfu x ml of milk.
*
p < 0.05; ** p < 0.01.
d
105
A. Sevi et al. / Small Ruminant Research 37 (2000) 99±107
tion involves the aggregation of casein micelles into a
network within which the fat is entrapped (Dalgleish,
1993).
Also, pH and clotting time were ameliorated by the
increasing number of lactations, but differences
among groups were smaller and not signi®cant for
these parameters.
The somatic cell count (SCC) in milk was not
changed by parity (Table 3). Average values were
acceptably low, ranging from 249 to 321 103
somatic cell/ml of milk in parities 3 and 1, respectively. Irrespective of parity, the highest values were
recorded in May and the lowest in February (671 and
203 103 somatic cell/ml of milk on average, respectively). SCC were higher than those found by Morgante et al. (1996) in Comisana ewes.
Conversely, the analysis of variance of the logarithmic values highlighted a marked effect of number
of lactations on milk bacteria counts. The P1 ewes
exhibited signi®cantly greater (p < 0.05) amounts of
mesophilic bacteria than the P2 and P3 ewes (521 vs.
348 and 298 103 cfu/ml, respectively) as well as
higher concentrations of psychrotrophs and total coliforms in their milk with respect to the P3 ewes (377 vs.
163 103 cfu/ml and 19 vs. 7 103 cfu/ml, respectively). Although the P1 ewes had a higher microorganism concentration in this milk, but there was no
increase in milk SCC. This could suggest that the
greater bacterial colonisation of the udder in these
ewes could be attributed to a reduced ef®ciency in the
natural defence mechanisms against the penetration
and multiplication of bacteria in the udder (Varner and
Johnson, 1983).
Increased concentrations of micro-organisms could
play a role in protein and fat contents decrease in the
milk yield of the P1 ewes, due to enhanced postsecretory lipolytic and proteolytic actions in milk by
enzymes produced from the bacterial ¯ora (Higoshi and
Hamada, 1975; Auldist et al., 1996; Sevi et al., 1999).
3.2. Incidence of subclinical mastitis
There were no cases of clinical mastitis during the
study period. One case of subclinical mastitis (Table 4)
was recorded in each group, but mastitis infection set
in progressively earlier as the number of lactations
decreased and this supports the hypothesis of less
ef®cient natural defence mechanisms in younger ewes,
Table 4
Cases of subclinical mastitis, bacteriologically positive milk
samples and bacteria isolated from milk of Comisana ewes in
parities 1 (P1), 2 (P2) and 3 (P3)
Parities
P1
P2
P3
January
February
March
April
May
0
1
1
1
1
0
0
1
1
1
0
0
0
1
1
Bacteriologically positive milk samples
January
February
March
April
May
2
2
5
3
3
1
1
3
4
2
1
2
1
3
2
Cases of subclinical mastitis
Bacteria isolated and number of milk samples from which isolated
Escherichia coli
6
4
4
Pseudomonas spp.
2
2
2
Pseudomonas aeruginosa
2
1
1
Staphylococcus aureus
2
1
0
Staphylococcus xylosus
0
1
1
Staphylococcus hyicus
1
0
0
Other CN-staphylococci
3
3
1
Streptococcus agalactiae
0
0
0
Streptococcus pneumoniae
1
1
0
Enterococcus spp.
6
6
3
Other streptococci
3
2
2
perhaps due to a less advanced development of the
immune system or to greater susceptibility to environmental stress (Bertoni, 1996). Exposure to bacteria
is a prerequisite but the development of infection and
mastitis is a balance between the natural defence
mechanisms of the teat and mammary gland and
the number and pathogenicity of the micro-organisms
in contact with the entrance of the teat canal (Klastrup
et al., 1987).
As a consequence, the number of bacteriologically
positive milk samples was higher in the P1 group
(n 15) than in the P2 (n 11) and P3 groups
(n 9). On the whole, bacteria or combinations of
bacteria were isolated from 35 milk samples and
environmental bacteria were largely predominant.
Streptococci (especially Enterococcus spp.) constituted the majority of bacteria isolated, since they were
isolated from about 70% of the 35 bacteriologically
106
A. Sevi et al. / Small Ruminant Research 37 (2000) 99±107
positive milk samples. E. coli, coagulase-negative
(CN)-staphylococci and Pseudomonas spp. were isolated from 14, 10 and 6 milk samples at 40, 29, 17%,
respectively. S. aureus and P. aeruginosa were detected
in four and three milk samples, respectively, whereas S.
agalactiae was not isolated from any milk sample.
4. Conclusions
Ewes milk yield was not changed by parity, but milk
protein, casein and fat contents increased and renneting ability of milk improved as the number of lactations advanced. Somatic cell counts in milk were very
similar in parities 1, 2 and 3 and groups had one case
of subclinical mastitis each. However, bacteria counts
in milk increased and mastitis infection set in progressively earlier with lower numbers of lactations.
Further studies on this topic are required using
larger ¯ocks. Nevertheless, our ®ndings indicate that
the differences in milk composition linked to the
number of lactations may depend on different endocrine and metabolic status in ewes of varying ages.
Also, most scrupulous control of sanitation of housing,
equipment and personnel is necessary.
References
Andrew, R.J., Kitchen, B.J., Kwee, W.S., Duncalfe, F., 1983.
Relationship between individual cow somatic cell count and the
mastitis infection status of the udder. Aust. J. Dairy Technol.
38, 71±74.
AOAC, 1990. Of®cial Methods of Analysis, 15th ed. Association of
Of®cial Analytical Chemists, Washington, DC, pp. 69±88.
Auldist, M.J., Coats, S., Rogers, G.L., McDowell, G.H., 1995.
Changes in the composition of milk from healthy and mastitic
dairy cows during the lactation cycle. Austr. J. Exper. Agric. 35,
427±436.
Auldist, M.J., Coats, S., Sutherlans, B.J., Mayes, J.J., McDowell,
G.H., Rogers, G.L., 1996. Effects of somatic cell count and
stage of lactation on raw milk composition and the yield and
quality of cheddar cheese. J. Dairy Res. 63, 269±280.
Bergonier, D., Van de Wiele, A., Arranz, J.M., Barillet, F.,
Lagriffoul, G., Concordet, G., Berthelot, X., 1994. Noninfectious factors affecting somatic cell count in dairy sheep
and goat. In: Rubino, R. (Ed.), Somatic Cells and Milk Quality
in Small Ruminants, pp. 139±167.
Bertoni, G., 1996. Environment feeding and milk quality.
Informatore Agrario (Suppl.) 52, 5±41.
Casoli, C., Duranti, E., Morbidini, L., Panella, F., Vizioli, V., 1989.
Quantitative and compositional variations of Massases sheep
milk by parity and stage of lactation. Small Rumin. Res. 2,
47±62.
Dalgleish, D.G., 1993. Bovine milk protein properties and the
manufacturing quality of milk. Livst. Prod. Sci. 35, 75±93.
Dell'Aquila, S., Pilla, A.M., Catillo, G., Scardella, G., Taibi, L.,
1993. Milk yield of Comisana, Delle Langhe, Massese, Sarda
and crossbred ewes. Zootecnica Nutrizione Animale 14, 95±102.
Dulin, A.M., Paape, M.J., Berkow, S., Hamosh, M., Hamosh, P.,
1983. Comparison of total somatic cells and differential cellular
composition in milk from cows, sheep, goats and humans.
Federation Proceedings 42, 1331.
Fox, L.K., Chester, S.T., Hallberg, J.W., Nickerson, J.W., Pankey,
J.W., Weawer, L.D., 1995. Survey of intramammary infections
in dairy heifers at breeding age and ®rst parturition. J. Dairy
Sci. 78, 1619±1628.
Fruganti, G.S., Ranucci, S., Tesei, B., Valente, C., 1985.
Assessment of the health status of ewes udder throughout
lactation. Clinica Veterinaria 108, 286±296.
Grummer, R.R., 1991. Effect of feeding on the composition of milk
fat. J. Dairy Sci. 74, 3244±3257.
Hart, I.C., 1983. Endocrine control of nutrient partition in lactating
ruminants. Proc. Nutr. Soc. 42, 181±194.
Hartman, P.A., 1989. The MUG (gluconidase) test for Escherichia
coli in feed and water. In: Balows, A., Tilton, R.C., Turano, A.
(Eds.), Rapid Methods and Automation in Microbiology and
Immunology, Brixion Academic Press, Brescia, Italy, pp. 290±
308.
Hatziminaoglou, I., Geogordiudis, A., Karalazos, A., 1990. Factors
affecting milk yield and proli®cacy of Karagouniko sheep in
West Thessaly (Greece). Livst. Prod. Sci. 24, 181±186.
Higoshi, H., Hamada, S., 1975. Proteolytic and lipolytic activities
of psychrotrophic bacteria originated from raw milk. J. Food
Hyg. Soc. Japan 17, 1±47.
IDF, 1964. Determination of the casein content of milk. IDF
Standard No. 29. International Dairy Federation, Brussels,
Belgium.
IDF, 1985. Enumeration of coliforms. IDF Standard No. 73A.
International Dairy Federation, Brussels, Belgium.
IDF, 1990. Determination of milk fat, protein and lactose content
Ð Guide for the operation of mid-infra-red instruments. IDF
Standard No. 141B. International Dairy Federation, Brussels,
Belgium.
IDF, 1991a. Enumeration of micro-organisms Ð Colony count at
308C. IDF Standard No. 100B. International Dairy Federation,
Brussels, Belgium.
IDF, 1991b. Enumeration of psychrotrophic micro-organisms Ð
Colony count at 6.58C. IDF Standard No. 101A. International
Dairy Federation, Brussels, Belgium.
IDF, 1995. Enumeration of somatic cells. IDF Standard No. 148A.
International Dairy Federation, Brussels, Belgium.
Klastrup, O., Bakken, G., Bramley, J., Bushnell, R., 1987.
Environmental in¯uences on bovine mastitis. Bulletin No.
217. International Dairy Federation, Brussels, Belgium.
Lee, C.S., Outteridge, P.M., 1981. Leucocytes of sheep colostrum,
milk and involution secretion, with particular reference to
ultrastructure and lymphocyte sub-popolations. J. Dairy Res.
48, 225±237.
A. Sevi et al. / Small Ruminant Research 37 (2000) 99±107
Morgante, M., Ranucci, S., Pauselli, M., Casoli, C., Duranti, E.,
1996. Total and differential cell count in milk of primiparous
Comisana ewes without clinical signs of mastitis. Small Rumin.
Res. 21, 265±271.
Pulina, G., 1990. In¯uence of feeding on ewes milk quality.
Informatore Agrario 37, 31±39.
Sandrucci, A., Tamburini, A., Rapetti, L., 1992. A study on the use
of a linear score for the evaluation of milk somatic cell count.
Proceedings of the 27th Simposio Internazionale di Zootecnia,
SocietaÁ per il Progresso della Zootecnia, Milan, Italy, pp. 175±190.
SAS, 1990 SAS/STAT User's Guide Version 6, 4th ed., Statistical
Analysis System Inst, Cary, NC.
Sevi, A., Massa, S., Annicchiarico, G., Dell'Aquila, S., Muscio, A.,
1999. Effect of stocking density on ewes milk yield, udder
health and micro-environment. J. Dairy Res., in press.
Shapiro, S.S., Wilk, M., 1965. An analysis of variance test for
normality. Biometrika 52, 591±601.
Ubertalle, A., 1989. Factors affecting the quality of ewes milk.
Proceedings of The Accademia Economico-agraria dei Georgo®li, Stamperia Editoriale Parenti, Firenze, Italy, pp. 1±18.
107
Ubertalle, A., Bianchi, M., Errante, J., Battaglini, L.M., 1990.
Proli®cacy and milk yield: phenotypic relationships in Delle
Langhe ewes. Zootecnica Nutrizione Animale 16, 219±224.
Varner, M.A., Johnson, B.H., 1983. In¯uence of adrenocorticotropin upon milk production, milk constituents, and endocrine
measures of dairy cows. J. Dairy Sci. 66, 458±465.
Watkins, G.H., Burriel, A.R., Jones, J.E.T., 1991. A ®eld
investigation of subclinical mastitis in sheep in Southern
England. Br. Vet. J. 147, 413±420.
Wever, P., Emanuelson, U., 1989. Effects of systematic in¯uences
and intramammary infection on differential and total somatic
cell counts in quarter milk samples from dairy cows. Acta Vet.
Scandin. 30, 465±474.
Wohlt, J.E., Kleyn, D.H., Vandernoot, G.W., Selfridge, D.J.,
Novotney, C.A., 1981. Effect of stage of lactation, age of
ewe, sibling status and sex of lamb on gross and minor
constituents of Dorset ewe milk. J. Dairy Sci. 64, 2175±2184.
Zannoni, M., Annibaldi, S., 1981. Standardisation of the renneting
ability of milk by Formagraph. Scienza e Tecnica LattieroCasearia 32, 9±94.