M . Serrano et al. Livestock Production Science 67 2001 253 –264
255
iances among repeated records has been proposed yield and protein percentage TD records. Given the
Kirpatrick et al., 1994; Meyer and Hill, 1997 to large size of the data set available 94,191 lactation
reduce the number of parameters to fit when there records and 70,207 pedigree records, several edits
are many measures for each individual taken over were performed so that the data set was more
time which are considered as different traits. manageable and a better correspondence between test
In this study, a genetic evaluation model is defined day number and date of test was achieved. First TD
and genetic parameters are obtained for TD milk between days 30 and 72 from parturition and time
yield and protein percentage records in two different interval between successive tests of more than 25
Spanish dairy sheep breeds. Some considerations are days and less than 35 days were forced. In addition,
made to develop the models. Firstly, since in dairy a minimum milk yield in each test of 200 ml and no
ewes there are generally four TD records in a missing values for any TD were required. Identifica-
lactation in contrast to the 10 in dairy cattle, compu- tion of dam and number of lambs born plus existence
tational demands are much smaller and allow a of both milk and protein percentage records were
multivariate approach within lactation. Secondly, also required. Finally, data were sampled by HYS
dairy sheep herds have a larger average size than CG, discarding CG with less than six observations.
dairy cattle herds, which partially avoids problems After these edits, 22,804 milk yield and protein
with HTD CG size. percentage TD records from 5701 first lactation ewes
of 32 herds were kept and used to estimate genetic parameters. The pedigree file consisted of 10,883
2. Material and methods animals.
Table 1 shows data and pedigree characteristics 2.1. Data
for both breeds. In the Manchega breed, there were no missing values for any TD. However, in the Latxa
Data for two Spanish dairy sheep breeds, Latxa records, missing values for the 3rd and 4th TDs were
and Manchega, were available. These breeds are accepted. In the Latxa case, the sires included in the
representative of two different regions of Spain. The pedigree file are artificial insemination AI and
Latxa breed is located in the Basque Country, a wet natural mating males. In the Manchega breed, only
region in the north of Spain. Manchega animals are AI males were included in the pedigree file. In the
raised in a semiarid region of central Spain, the pedigrees, 23 of Latxa and 19 of Manchega
Autonomous Community of Castilla-La Mancha. animals have a known sire and dam. The percentage
TD records from one variety of Latxa dairy sheep of base animals was 31 and 32 for Latxa and
Blond-Faced were collected between 1993 and Manchega breeds, respectively.
1998. Data consisted of 28,950 first lactation milk Means and standard deviations for TD milk yield
yield records. Some restrictions were applied to and protein percentage records, days in milk and
achieve the final data set. A minimum milk yield in number of TD considered are presented in Table 2
the 1st and 2nd TDs of 200 ml and in the 3rd and 4th for each breed.
TDs of 100 ml plus identification of number of lambs born were required. First TD between days 10
Table 1
and 72 from parturition and time interval between
Data and pedigree characteristics
successive TD of more than 20 and less than 40 days
Manchega Latxa
were forced. Missing values for the 2nd, 3rd and 4th TD were accepted. After these edits, 20,046 milk
Pedigree animals 10,883
10,192
yield TD records from 5998 first lactation ewes of 40
Sires 307
212 Dams
5729 4766
herds were available and used for variance com-
Animals with known sire and dam 2061
2373
ponent estimation. The pedigree file consisted of
Animals with known dam 5348
4595
10,192 animals.
Animals with unknown sire and dam 3474
3224
Data for the Manchega breed were collected
Data TD records 22,804
20,046
between 1979 and 1996 and contained both milk
256 M
. Serrano et al. Livestock Production Science 67 2001 253 –264 Table 2
equations of the animal models applied in each case
Raw means and standard deviations of test day milk yields ml,
were the following.
protein percentage, days in milk and number of TD considered for
Multivariate
both breeds
MHYS: y
5 m 1 HYS 1 nlb 1 age
ijklmn in
j k
Test Manchega Latxa
day 22,804 test day 20,046 test day
1 bdim 1 g
1 ´
ln mn
ijklmn
Days in milk 1
47.3369.25 41.52615.07
2 77.2369.57
72.66615.46
MHTD: y
5 m 1 HTD 1 nlb 1 age
ijklmn in
j k
3 107.1769.86
102.66615.70 4
136.95610.15 132.31616.20
1 bdim 1 g
1 ´
ln mn
ijklmn
Milk yield ml 1 1237.036605.37
1162.506497.87
Univariate
2 1113.236583.47
976.586417.53 3
924.386486.25 786.426330.97
UHYS: y
5 m 1 HYS 1 nlb 1 age
ijklmn i
j k
4 697.166397.25
657.066295.46
1 bdim 1 g 1 p 1 ´
Protein 1
5.2060.63 –
l m
m ijklmn
percentage 2
5.4660.66 –
3 5.8160.75
–
UHTD: y
5 m 1 HTD 1 nlb 1 age
ijklmn i
j k
4 6.1860.87
–
1 bdim 1 g 1 p 1 ´
l m
m ijklmn
No. of TD 1
5701 5998
records 2
5701 5998
where y is the nth test day milk yield or protein
ijklmn
3 5701
5064
percentage record within lactation for the ith CG
4 5701
2986
HYS or HTD of the mth ewe of age k at lambing age with jth number of lambs born nlb and in the
lth lactation stage measured in days in milk dim on 2.2. Statistical analysis
the nth TD; m is the population mean; HYS is the
in
fixed effect herd-year-season of parturition on the Variance components estimation was carried out
nth TD 213 levels in Latxa and 193 levels in by DFREML using VCE 4.2.5 software Groeneveld
Manchega; HTD is the fixed effect herd-year-
in
´ ´
and Garcıa Cortes, 1998. Alternative animal models month of TD on the nth TD 659, 667, 538 and 370
were used to compare different CG definition and levels for the 1st, 2nd, 3rd and 4th Latxa TD,
trait treatment. The analysis was developed for two respectively, and 239 levels for all TDs in Manchega
traits: TD milk yield in both breeds and protein under the multivariate model, and 974 levels in
percentage only in Manchega breed. Latxa and 692 levels in Manchega in the univariate
Models were based on several studies in which TD approach; nlb is the fixed effect number of lambs
j
traits in dairy sheep were involved Baro et al., 1994; born two levels in both breeds; age is the fixed
k
El-Saied et al., 1998; Serrano et al., 1998. Age at effect age at lambing four levels in both breeds;
parturition, number of lambs born, days in milk and bdim is the days in milk on the nth TD as a
ln
several CG combinations were the fixed effects more covariate, b is the linear regression coefficient of y
commonly used in these works. All these effects on dim; g
is the additive genetic effect for the mth
mn
were highly significant and were therefore included animal on the nth TD; p
is the permanent en-
m
in the evaluation models. vironmental effect for the mth animal 5998 levels in
First analyses, considering TD as different traits, Latxa and 5701 levels in Manchega; and ´
is
ijklmn
were carried out under multivariate animal models the residual.
with two different CG definitions: herd-year-season Due to the different management of animals in
of parturition MHYS and herd-year-month of TD each breed, season of lambing was considered in two
MHTD. Subsequent analyses were carried out periods in Latxa ewes August–December and
following a univariate approach, considering TD as January–June and monthly in the case of the
repeated measures of the same trait UHYS and Manchega breed. Number of lambs born was defined
UHTD, respectively, for HYS and HTD CG. The in two classes corresponding to parities with one and
M . Serrano et al. Livestock Production Science 67 2001 253 –264
257
two or more lambs born for both breeds. Age at Latxa and smaller |100 ml for the 1st and 4th TD.
lambing was defined as a four class fixed effect. In TD protein percentage showed an opposite trend to
Latxa ewes, classes were defined in years 1, 2, 3 that observed for TD milk yield. There was an
and 4 or more years. In the Manchega breed, these increase of protein percentage from the 1st to the 4th
four classes were considered in months 15, 16– test day records approximately 1. Similar trends
17, 18–20 and 20 months. of milk yield and protein percentage along lactation
have been found in Churra ewes Fuertes et al., 1998.
3. Results and discussion Variance component estimates residual R and
