236 R
.C. Dobos et al. Livestock Production Science 63 2000 235 –243
1. Introduction compared to heifers grown on an alfalfa based diet
22 CP. Milk production was not affected by Dairy heifers grown to achieve liveweight gains
either diet, LWG or LWG within diet. However, LWG greater than 800 g per d before puberty have
heifers on the high-CP diet produced 1.0 kg per d significantly reduced milk yields in some studies
less fat-corrected milk, independent of pre-pubertal Amir and Kali, 1974; Gardner et al., 1977; Little
LWG. and Harrison, 1981; Sejrsen et al., 1982; Valentine et
There is continuing pressure for dairy managers to al., 1987; Waldo et al., 1989, but not in others
reduce costs of production. Reducing age at first Capuco et al., 1988; van Amburgh and Galton,
breeding is an option but there is a need to determine 1994; Capuco et al., 1995; Pirlo et al., 1997. This
if diet composition can alleviate the negative effects lack of consistency has been attributed to the differ-
of high LWG during the pre-pubertal period. Sejrsen ent feeding standards used Sejrsen, 1994, and also
and Foldager 1992 suggested that type of diet may to diet composition Kertz et al., 1987.
not be important at lower LWG. They found no Kertz et al. 1987 suggested that the lower milk
effect on mammary parenchyma of diets based on yield because of high pre-pubertal LWG could be
straw in heifers at low feeding levels. prevented by increasing the dietary crude protein
The objective of this experiment was to determine CP concentration within this period. However,
the effect of dietary protein concentration and investigations conducted by van Amburgh and Gal-
amount of protein protected from rumen degradation ¨
ton 1994 and Mantysaari et al. 1995 indicated no REP within iso-energetic diets on mammary gland
effect of dietary CP concentration on milk pro- development and subsequent production of dairy
duction and mammary gland development, respec- heifers grown at LWG in excess of 900 g per d
tively. Pirlo et al. 1997 investigated the effects of before puberty.
various levels of dietary energy and CP fed to Italian Friesian heifers between 100 and 300 kg liveweight
on milk production during first lactation. Heifers
2. Materials and methods
consuming the diets with 110 recommended CP NRC, 1989 at either 110 or 90 recommended
2.1. Study location NRC, 1989 energy concentration had significantly
higher protein concentrations in their milk. Although This experiment was conducted at NSW Agricul-
there was no influence of either dietary energy or CP ture’s Elizabeth Macarthur Agricultural Institute
on milk and fat yield, heifers that consumed the EMAI, Camden during the period from birth to
high-energy 110 NRC, 1989, low-CP 90 three months gestation and at the Dairy Research
NRC, 1989 diet, produced 1.6 kg per d less milk Foundation, University of Sydney, Camden from
than heifers that consumed the high-energy, high-CP three months of pregnancy to the completion of the
110 NRC, 1989 diet. Milk and fat yields were first lactation. The experiment was approved by
not influenced by dietary CP concentrations within NSW Agriculture’s Animal Care and Ethics Commit-
the low-energy 90 NRC, 1989 diets. Pirlo et al. tee at EMAI 94 12.
1997 concluded that Italian Friesian heifers can tolerate LWG in excess of 800 g per d between
dietary energy and CP concentrations of 90–110 2.2. Pre-pubertal feeding period
recommendations NRC, 1989. Mammary gland growth is reduced during the
Sixty-three Friesian heifers were blocked by age pre-pubertal period when high-energy diets are con-
and liveweight LW and randomly assigned within sumed to achieve early breeding ages Sejrsen et al.,
blocks to one of three treatment diets from five to ten 1982. Capuco et al. 1995 found that pre-pubertal
months of age. Because heifers entered the experi- heifers grown in excess of 900 g per d on a corn
ment at two distinct periods, two subgroups per based diet 15 CP had reduced mammary DNA
treatment diet N 5 10 and N 5 11 were formed to
and increased weight of gland and mammary fat avoid the interactions of social influences on diet
R .C. Dobos et al. Livestock Production Science 63 2000 235 –243
237
intake. Heifers were kept and fed in feedlot type To ensure adequate fibre intake, sorghum Sor-
pens, with two pens per treatment. ghum sudanense hay 8.0
60.1 MJ ME per kg DM; The ingredient and chemical composition of the
80 66.2 g CP per kg DM was added to the pellets at
pelleted diets fed to heifers within the pre-pubertal a maximum of 30 by wet weight at each feeding.
period is given in Table 1. Total mixed diets were formulated to be iso-ener-
getic but differed in level of CP and REP Table 2. Each mixed diet was offered ad libitum at 1400 h
Table 1 Ingredient and chemical composition of the three pelleted pre-
and the consumption was calculated on a group basis
pubertal diets
at the end of each week. Heifers were weighed
a
weekly from entry until the end of the pre-pubertal
Ingredients kg per 100 kg Diet
feeding period.
A B
C
Total intake of each mixed diet during the pre-
Sorghum 36.39
12.05 26.46
pubertal feeding period was similar P . 0.05 for all
Wheat 0.00
20.00 0.00
groups 12.7 vs. 12.4 vs. 12.3 t DM, with no
Millrun 50.06
60.00 55.99
evident ill-effects from consuming the treatment
Meat meal 0.00
0.00 4.85
Cottonseed meal 8.00
0.00 11.75
diets. Four heifers consuming diet C did not calve, as
Tallow 1.55
1.75 0.00
one was an inter-sex freemartin, one had an uterine
Limestone 2.20
0.00 0.00
torsion and two were not in-calf for unknown
Salt 1.00
0.00 0.00
reasons.
Enfield dairy premix 0.75
0.75 0.20
Dicalcium phosphate 0.00
2.20 0.25
Sodium bicarbonate 0.00
0.50 0.50
2.3. Pre-pubertal diet analyses
Urea 0.00
2.25 0.00
Weekly samples of each mixed diet were compo-
Chemical composition g per kg DM
sited at the end of the pre-pubertal feeding period for
ME MJ per kg DM 11.00
10.86 10.99
analysis of ME, CP and in sacco degradability
Crude protein 139.80
182.00 179.90
Fat 507.00
511.00 40.60
characteristics. ME was determined according to
Fibre 60.20
59.80 68.30
SCA 1990, while CP was calculated by multiplying
Calcium 9.10
6.00 6.60
the total nitrogen content by 6.25. Total nitrogen
Phosphorous 4.60
8.10 8.10
content was determined by a Kjedahl procedure
a
Diet A 5 high-energy, low-CP, high-REP; diet B 5 high-
AOAC, 1980 using a Kjeltec Auto 1030 Tecator
energy, high-CP, low-REP; Diet C high-energy, high-CP, high-
AB, Sweden.
REP.
In sacco degradability of protein was determined
REP 5 Undegradable
protein; DM
5 dry matter;
ME 5
metabolisable energy estimated from SCA 1990.
using three Hereford heifers mean liveweight 444
Table 2 Metabolisable energy, crude protein, undegradable protein and in sacco degradability characteristics for the three diets fed to pre-pubertal
heifers
a
Parameter Diet
A B
C Metabolisable energy ME MJ per kg DM
10.99 11.12
10.89 Crude protein g CP per kg DM
142.00 183.20
182.30 REP g REP per kg CP
270.00 133.00
267.00 a g per kg CP
254.00 517.00
328.00 b g per kg CP
563.00 404.00
521.00 c g per h
0.11 0.13
0.07
a
Diet A 5 high-energy, low-CP, high-REP; Diet B 5 high-energy, high-CP, low-REP; Diet C 5 high-energy, high-CP, high-REP.
REP 5 Undegradable protein; a 5 the immediately soluble component; b 5 the slowly but potentially degradable component; c 5 rate of
disappearance of b at an outflow rate of 0.02 per h.
238 R
.C. Dobos et al. Livestock Production Science 63 2000 235 –243
kg fitted with rumen cannulae. Data on N residues 9.3
60.4 MJ ME; 175611.9 g CP per kg DM to were fitted to the equation of Ørskov and MacDonald
ensure a LWG of 700 g per d. During lactation, 1979 to determine the in sacco degradability
heifers grazed irrigated kikuyu 9.5 60.6 MJ ME;
characteristics of each mixed diet. The amount of 128
610.3 g CP per kg DM in summer and annual REP in each diet was calculated according to AFRC
rye-grass in winter 10.9 60.6 MJ ME; 269613.2 g
1993. Table 2 shows the metabolisable energy ME CP per kg DM and were supplemented with maize
MJ per kg DM, CP g per kg DM, REP g per kg silage when the pasture did not meet requirements.
CP and in sacco degradability characteristics of the Each heifer was offered pellets 5.0 kg per d as fed,
three mixed diets. 12
60.2 MJ ME and 24168.2 g CP per kg DM at both morning and afternoon milking.
Using a tape measure, udders were measured for 2.4. Post-puberty to three months before calving
circumference, length and breadth on the same day 3 h after morning milking mean
6SE days in milk, At the end of the pre-pubertal feeding period,
196.2 65.37.
heifers were grouped as one herd. LW was recorded at weekly intervals. During the autumn and winter
the heifers grazed pastures consisting of annual 2.6. Slaughter protocol
ryegrass Lolium multiflorum, 10.7 60.06 MJ ME,
269 616.1 g CP per kg DM and dryland lucerne
Once heifers reached 16 months of age and were Medicago sativa, 9.7
60.4 MJ ME, 202621.5 g CP between 10 and 18 days after oestrus, six heifers per
per kg DM, while in spring and summer they grazed group were stunned and immediately exsanguinated
irrigated kikuyu Pennisetum clandestinum, 9.4 60.3
at the abattoir. Udders were carefully removed MJ ME, 136
613.7 g CP per kg DM and dryland within 5 min of death and placed in a bucket of ice
lucerne. In times of pasture shortage, the herd was for transportation to the laboratory. The udder was
offered pellets diet B, sorghum silage 6.2 60.6 MJ
weighed before and after the removal of skin, teats, ME, 109
612.4 g CP per kg DM and lucerne hay parts of median suspensory ligaments, supramam-
9.3 60.4 MJ ME, 175611.9 g CP per kg DM. The
mary lymph nodes and excess adipose tissue. Udders target LWG in the post-pubertal period was set to be
were then dissected into left and right halves down between 550 and 700 g per d.
the median suspensory ligament and weighed. Both At 15 months of age, heifers were injected with 2
halves were frozen at 2 208C for later preparation of
ml Estrumate Mallinckrodt Vet Ltd., distributed by gland slices and biochemical analyses. At slaughter
Jurox Pty. Ltd. at day one of mating to synchronise carcasses were weighed hot and 24 h later assessed
oestrus. A heat mount detector Unistar Pty Ltd was for fat depth 12 13th rib and weighed cold.
applied to each heifer and heifers in oestrus were presented to an Angus bull. Pregnancy was diag-
2.7. Mammary gland analyses nosed by rectal palpation 90 days after the last
individual mating and if diagnosed as pregnant were The right half of the udder was cut into slices of
removed from the mating group. about 5 mm thickness using a meat slicer. Slices
were made in the parasaggital plane, progressing 2.5. Three months before calving to end of first
from the medial aspect to the most lateral portion of lactation
the gland. Traces on acetate sheets were then made of each slice to determine the fat to secretory tissue
Heifers were weighed at monthly intervals. During ratio. Each trace was photocopied and tissue types
lactation, milk yield and a composite daily sample separated by cutting. Photocopied traces were cut
for analysis of milk fat and protein were obtained into fat and secretory tissue equivalents, weighed and
monthly. Before calving heifers grazed kikuyu pas- the ratio of fat to secretory tissue determined. The
tures 9.0 60.3 MJ ME; 160612.1 g CP per kg DM
left udder half was cut into small cubes 60–80 mm and they were supplemented with lucerne hay
and minced in a meat mincer. Aliquots were taken
R .C. Dobos et al. Livestock Production Science 63 2000 235 –243
239
and freeze dried for the determination of moisture. effects were each heifer within each month of
Freeze dried aliquots also were used to determine lactation. The variance component estimation meth-
lipid content Folch et al., 1957 and amount of dry od was restricted maximum likelihood REML and
fat free tissue DFFT. Duplicate samples of DFFT the type of covariance matrix was compound sym-
were used to determine the amount of DNA Martin metry.
et al., 1972, hydroxyproline Bergman and Loxley, 1963 and nitrogen in the udder. The hydroxyproline
value was converted to collagen using a factor of
3. Results
