Results and discussion Variance component estimates residual R 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

additive genetic G associated with the first lactation Average days in milk DIM, milk yield and TD milk yields under multivariate animal models are protein percentage only in Manchega breed for shown in Table 3. In both data sets and breeds a each TD and breed in the first lactation data set are decrease of residual variance from the 1st to the 4th presented in Table 2. The average DIM at each TD TD was observed. This pattern is similar to that was larger in the Manchega breed. The standard found in cattle by Swalve 1995. The first TD had deviation of DIM was high in all TD for Latxa ewes, the highest residual variance estimate in both breeds due to the less strict criteria used to define the and models. Differences were more evident in Latxa intervals between TD. Average TD milk yields in the data. Uncontrolled environmental factors seem more Manchega breed were always higher than in the likely to occur at the onset of lactation and might be Latxa breed, due to differences in lactation stage at a possible explanation for this observed trend. the time of collection. These differences were higher In the Latxa breed, residual variances estimated for the 2nd and 3rd TD 140 ml than for the 1st and under the MHTD model were smaller than those 4th TD 75 and 40 ml, respectively. Standard estimated with the MHYS model. This indicates, as deviations for the 2nd and 3rd TD milk yields in the expected, that more environmental variation is re- Manchega breed were 160 ml larger than those for moved by considering comparisons of animals within Table 3 Test day milk yield ml residual R and genetic G variances diagonal and covariances above diagonal estimated under multivariate animal models including HYS MHYS or HTD MHTD contemporary groups with first lactation data of Latxa and Manchega ewes Model TD Latxa Manchega 1 2 3 4 1 2 3 4 R MHYS 1 134,648 47,732 26,841 14,188 118,286 48,325 37,205 28,219 2 90,889 35,809 20,914 101,217 47,096 36,299 3 57,602 17,997 73,621 38,828 4 49,396 60,737 MHTD 1 123,314 45,063 25,021 10,918 116,619 50,999 37,876 27,258 2 80,059 30,644 16,462 101,589 47,715 35,200 3 51,672 13,923 75,260 37,998 4 42,983 59,700 G MHYS 1 34,361 29,726 24,804 18,651 36,744 31,360 19,644 9884 2 30,414 23,716 17,366 35,038 26,304 15,472 3 24,477 21,893 26,146 16,338 4 21,644 12,470 MHTD 1 34,001 25,712 21,724 18,301 38,276 31,677 20,378 12,149 2 24,066 19,836 17,347 33,056 26,451 17,452 3 20,263 20,360 24,563 17,424 4 22,069 13,100 258 M . Serrano et al. Livestock Production Science 67 2001 253 –264 the day on which the record is made than by In the Latxa breed, the TD milk yield genetic comparing animals at the same period of parturition variance estimates were higher under the MHYS Rekaya et al., 1999. However, in the Manchega model than under the MHTD model, these differ- breed, the differences in residual variances between ences being more evident for the second and third alternative models were not so clear. The first and TDs. Only the fourth TD showed a smaller genetic fourth TDs showed smaller residual variances under variance. In the Manchega breed, the 2nd and 3rd the HTD model, however these were higher for the TD records showed greater genetic variance esti- second and third TDs. In the Latxa breed, HYS CG mates with the HYS model. On the other hand, was widely spread over 5 months of the lambing higher genetic variance estimates were found for the period two lambing periods in the year: September– 1st and 4th TD records under the HTD model. In December and January–June. However, in Man- general, higher genetic variance estimates were chega ewes, parturition season was defined in obtained in the Manchega than in the Latxa breed. months over the year. In the first case, the MHTD Genetic covariance estimates, as for the residual model captured environmental variation that was not ones, were higher between adjacent TD records. In accounted for by the MHYS model. In Manchega, the Latxa breed, these values were higher for the the MHTD model did not show the same advantage, MHYS model than for the MHTD model. In the because of the greater similarity between the CG, Manchega breed, the opposite trend was observed. HYS and HTD definitions. Thus HTD models seem Higher genetic covariances were estimated under the to decrease residual variances in relation to HYS MHTD model than under the MHYS model. models, depending on the definition of HYS CG. Although at the level of variance component Residual covariance estimates showed higher val- estimation some advantages of HTD over HYS were ues between adjacent TD records under both models observed in this study, it is important to take into and in both breeds. These covariances had higher account the reduction in CG size produced by fitting values in the MHYS model than in the MHTD model HTD rather than HYS effects. Using HTD resulted for the Latxa breed but not in Manchega, where both in considerably smaller CG subclasses which would models showed similar residual covariance values. affect sire evaluation. Meyer et al. 1989 found in Genetic variances had a similar trend along lacta- their study a great increase in terms of percent tion as observed for the residual variances. In both information lost of single sire subclasses when fitting breeds and models, genetic variance estimates de- HTD rather than HYS effects. In our case, the CG creased with time, from the 1st to the 4th TD record. was similarly affected in the multivariate TD ap- However, these changes among TDs were smaller proach. In Latxa, changes in CG size ranged from 24 than in the previous case. Again, the 1st TD record to 58 CG with less than six records when fitting had the highest variance value. In this case, results HYS or HTD effects, respectively. In Manchega, this did not agree with those obtained in cattle Swalve, reduction was smaller due to more stringent data 1995; Kettunen et al., 1997; Rekaya et al., 1999, selection, which included only HYS CG with at least where additive genetic variance estimates increased six records. In this case, 8 of CG presented less from the 1st to the 4th TD milk yield. This could be than six records in the HTD model. This last case is due to the fact that, in cattle, there is no suckling not representative of practice, because, in the whole period because calves are weaned 2 or 3 days from milk recording program of this breed, there are parturition. Thus, the first TDs were collected in the numerous herds of small size, which also implies ascendant phase and peak of the lactation curve. small CG sizes. This is avoided in the Manchega However, generally, TD collection in sheep begins selection scheme by fitting HYS CG with mobile after the suckling period average 30 days from periods of parturition Jurado et al., 1995. However, parturition and, therefore, the first TDs are collected this kind of grouping is not possible for HTD effects. after the peak of the lactation curve. Rekaya et al. Therefore, one of the most important disadvantages 1999 reported a decrease in genetic variance from in considering a multivariate approach of TD models the 4th to the 10th TD. Our results might be in in sheep is the great reduction in CG size when the accordance with this last estimate. HTD effect is fitted. Also, variance component M . Serrano et al. Livestock Production Science 67 2001 253 –264 259 Table 4 estimates was observed. Residual variances increased Residual and genetic variances diagonal and covariances above along lactation, except for the 2nd TD, which diagonal test day protein percentage, estimated under multivariate showed the lowest residual variance for both models. animal models including HYS MHYS and HTD MHTD Additive genetic variance presented the same pattern, contemporary groups with first lactation data of Manchega ewes increasing from the 1st to the 4th TD. Model TD Manchega In this case, as expected, MHYS residual vari- 1 2 3 4 ances were slightly higher than those of MHTD for Residual MHYS 1 0.212 0.064 0.039 0.025 all TD records. Genetic variances showed an oppo- 2 0.180 0.054 0.041 site trend. Slightly higher values were obtained for 3 0.266 0.114 the MHTD model than for the MHYS model. Using 4 0.356 the HTD effect seems to enhance the detection of MHTD 1 0.205 0.058 0.036 0.026 differences among animals at the environmental 2 0.175 0.054 0.043 level, but not at the genetic level for this trait. 3 0.256 0.113 Residual covariances had similar trends as those 4 0.350 observed for TD milk yield records. Higher values Genetic MHYS 1 0.058 0.040 0.044 0.041 were found for adjacent TD records. However, 2 0.072 0.080 0.067 genetic covariance estimates showed different be- 3 0.089 0.075 havior. Genetic covariances among the 1st and other 4 0.118 TDs tended to be smaller than those estimated MHTD 1 0.058 0.045 0.047 0.043 between the 2nd and 3rd, 2nd and 4th and 3rd and 2 0.074 0.081 0.065 4th TDs. 3 0.092 0.076 Heritabilities and genetic correlations among TD 4 0.113 milk yield and TD protein percentage only in Manchega breed records for both breeds using estimation seems to be affected when a HYS or a alternative MHYS and MHTD models are shown in HTD CG is fitted. Models with HTD CG showed Table 5. Standard deviations ranged from 0.01 to smaller residual variances in most cases. 0.09. Table 4 shows TD protein percentage variance In the Latxa breed, no substantial differences in component estimates in the Manchega breed under genetic parameter estimates were observed between the two models considered, MHYS and MHTD. An alternative models. Similar heritability and genetic opposite trend to that of TD milk yield variance correlations were found with the MHYS and MHTD Table 5 2 Test day milk yield ml and protein percentage genetic parameters: heritability h at diagonal and genetic correlations above diagonal r g estimated under multivariate animal models including HYS MHYS and HTD MHTD contemporary groups with first lactation data of a Latxa and Manchega ewes Model TD Latxa Manchega Milk yield ml Milk yield ml Protein percentage 1 2 3 4 1 2 3 4 1 2 3 4 MHYS 1 0.20 0.92 0.85 0.68 0.23 0.87 0.63 0.46 0.21 0.61 0.60 0.50 2 0.25 0.87 0.67 0.25 0.87 0.74 0.28 0.99 0.72 3 0.29 0.95 0.26 0.90 0.25 0.73 4 0.30 0.17 0.25 MHTD 1 0.21 0.90 0.82 0.66 0.24 0.89 0.66 0.54 0.22 0.67 0.64 0.53 2 0.23 0.89 0.75 0.24 0.92 0.84 0.29 0.98 0.70 3 0.28 0.96 0.24 0.97 0.26 0.74 4 0.33 0.18 0.24 a Standard deviations for the heritability and genetic correlations ranged from 0.01 to 0.09. 260 M . Serrano et al. Livestock Production Science 67 2001 253 –264 models. The first TD milk yield record showed the decreasing to 0.66 when records were three TD lowest heritability value in both cases, due to the apart. In Manchega, genetic correlations between higher residual variance, which agrees with several adjacent TD took values of 0.87, decreasing to 0.46 results in cattle Meyer et al., 1989; Wiggans and when records were three TD apart. Higher genetic Goddard, 1997; Vargas et al., 1998; Rekaya et al., correlations in Latxa could be due to the less strict 1999. These results confirm that there is more criteria used to consider TD intervals in this breed. variation not accounted for by the models in the In this case, the period between consecutive TD initial stage of lactation. As reported in cattle studies, records are more spread over time 20 to 40 days heritabilities were generally lower in early lactation required between successive TD than those of Danell, 1982; Wilmink, 1987. Heritability values Manchega records 25 to 35 days. Therefore, in the increased along lactation, the last 4th TD being the Latxa breed, TD traits were mixed because the time one with the highest value 0.30 and 0.33 in MHYS interval for a TD trait was very long and thus genetic and MHTD models, respectively. The first and correlations were higher. Higher genetic correlations second TD records showed heritability values near among TD records were obtained by Barrillet and that estimated for standardized 120 day milk yield, Boichard 1994 with a sire model, concluding that 0.23 Ugarte et al., 1996. However, the 3rd and 4th considering TD data as repeated measures of the TD heritability values were clearly higher than those same trait seems to be a reasonable hypothesis. In estimated for the 120 day milk yield. the present case, the results did not lead to the same Heritability values in the Manchega breed pre- conclusion. Also, our estimates were lower than sented some differences to those found in Latxa. In those obtained by Georgoudis et al. 1997 in a study this breed, heritability of the 1st, 2nd and 3rd TD with a single herd of Chios and Kymi sheep breeds, records showed similar values within and across which found genetic correlation values among TD models. In this case, the 4th TD presented the milk yield records ranging from 0.73 to 0.99. smallest heritability values, 0.17 and 0.18 in MHYS Heritability for protein percentage TD records in and HTD models, respectively, due the smaller the Manchega breed showed slightly higher values residual and genetic variances. Also, insubstantial with the MHTD model. For this trait, the first TD differences were observed among genetic parameter record presented the smallest heritability value in estimates under alternative models. These heritability both alternative models. All heritability values were estimates were smaller than those of the standardized clearly lower than estimated in this breed for the 120 day milk yield, 0.33 with REML Serrano et al., standardized 120 day protein percentage, 0.35 with 1996b and 0.28 with a Bayesian approach Jurado et REML Serrano et al., 1996b, and similar to the al., 1997. estimate with a Bayesian approach, 0.29 Jurado et These results are in accordance with those ob- al., 1997. Also, Barrillet and Boichard 1994 found tained by Barrillet and Boichard 1994. These higher heritability for complete lactation 0.45 than authors found lower heritability estimates for TD for TD traits 0.35. Genetic correlations showed the milk yield average 0.25 than for complete lactation same trend as for milk yield. Higher genetic correla- 0.30. Our TD heritability estimates were similar to tions were obtained between adjacent TDs than for those obtained by Georgoudis et al. 1997, which two or three TDs apart. ranged from 0.19 to 0.26. However, these authors Table 6 shows variance components and genetic found lower heritability for commercial milk yield parameters heritability and repeatability estimated 0.16 than for TD traits. These estimates had large under alternative UHYS and UHTD univariate ani- standard errors, which ranged from 0.12 to 0.15. mal models considering TD milk yield and protein In both breeds and with the two models, genetic percentage only in Manchega breed records as correlations were always large between adjacent TD repeated measures of the same trait within first for milk yield. Generally, genetic correlations were lactation. Standard deviations of genetic parameters higher in the Latxa than in the Manchega breed ranged from 0.005 to 0.02. under both models. In the Latxa breed, genetic Small changes in genetic and permanent environ- correlations for adjacent TDs were at least 0.87, mental variances across alternative UHYS and M . Serrano et al. Livestock Production Science 67 2001 253 –264 261 Table 6 2 2 2 Test day milk yield ml and protein percentage residual s , genetic s and permanent environmental s variances and genetic e a c 2 parameters, heritability h and repeatability R estimated under univariate animal models including HYS UHYS and HTD UHTD a contemporary groups with first lactation data of Latxa and Manchega ewes 2 2 2 2 Breed Trait Model s s s h R e a c Latxa Milk yield UHYS 75,230 24,847 27,000 0.19 0.40 UHTD 58,014 23,973 27,883 0.21 0.47 Manchega Milk yield UHYS 86,093 22,103 29,786 0.16 0.37 UHTD 58,806 24,723 40,342 0.20 0.52 Protein UHYS 0.322 0.065 0.024 0.16 0.21 percentage UHTD 0.226 0.071 0.050 0.20 0.35 a Standard deviations for heritability and C squared ranged from 0.005 to 0.02. UHTD models were observed in the Latxa breed. In the case of protein percentage, TD records However, the estimated residual variance with the residual variances were lower in the UHTD model. UHTD model was smaller, as reported by Meyer et However, additive genetic and permanent environ- al. 1989. Heritability values were similar to those mental variances are greater in the UHTD model of the 1st TD in the multivariate analysis, 0.19 and than in the UHYS model. Heritability estimates were 0.21 for UHYS and UHTD, respectively. The re- similar to those obtained for TD milk yields, 0.16 peatability value was higher in the UHTD model and 0.20 for UHYS and UHTD respectively, and 0.47 than in the UHYS model 0.40, and superior smaller than values obtained in the multivariate to the estimate from a repeatability animal model approach. along lactation 0.42 Ugarte et al., 1996. In Churra ewes with a similar repeatability animal In Manchega data, changes in variance component model, Baro et al. 1994 found a heritability value estimates with UHYS and UHTD models were of 0.35 for test day milk yield. The inclusion of observed. Also in this case, the residual variance for natural mating and AI sires in the pedigree file the UHTD model was the lowest. However, perma- contributes to a better heritability estimation due to nent environmental variance showed a substantial more relationships being considered. However, increase from the UHYS to the UHTD model. In this heritability of protein percentage 0.13 was smaller case, there were large differences between different than values found in Manchega ewes. In Chios sheep models in heritability estimates. The UHTD model Georgoudis et al., 1997, the heritability estimate showed a higher value of this parameter 0.20 than for the first four TD records in a repeatability animal that observed with the UHYS model 0.16. Both model was 0.28 and for the seventh TD record 0.17. heritability estimates were clearly smaller than those Repeatability estimates were 0.39 and 0.40 in each of the multivariate approach. Repeatability estimates case. presented more differences across models than in the Under the univariate model, the CG size reduction case of Latxa. Repeatability was much higher in the had less impact. When a univariate approach is UHTD model than in the UHYS model in the considered by taking TD records as repeated mea- Manchega breed, 0.52 and 0.37, respectively. sures of the same trait within lactation, HTD CG Variance estimates were higher than those found includes all animals recorded on the same day by El-Saied et al. 1998 under a univariate TD independent of TD number. Thus HTD classes have model with HTD CG. Heritability and repeatability a larger size than in the multivariate approach. In values for TD milk yield were 0.14 and 0.44, Latxa, in the univariate TD approach, there were 8 respectively. In this case, HTD CG was not nested to and 33 of CG with less than six records when HYS TD number and multiple lactations were considered and HTD effects were fitted respectively. In Man- in the analysis. A single permanent environmental chega, 2 of CG groups had less than six records effect was fitted to account for TD repeated measures under the UHTD model. within and among lactations. The higher genetic variances and heritabilities 262 M . Serrano et al. Livestock Production Science 67 2001 253 –264 found under the multivariate than under the uni- using a multiple trait approach and a method to variate approach, in both breeds, traits and models, combine all information in a single animal breeding could be due to a better adjustment of environmental value may be a reason to use a repeatability model effects in the first case. CG and regression coefficient instead. However, the pattern in genetic correlations in DIM were different effects for each TD in among different TD traits suggests that a multiple multivariate models, however in the univariate ap- trait approach is more accurate than the repeatability proach, these are the same effects for all TD records. model. The use of random regression models RRM Therefore, multivariate models might fit the data or covariance functions CF would also allow better and subsequently higher heritability values are acknowledgement of changes in the trajectory of obtained. random effects genetic and or environmental and their associated covariances with time. However, the advantage of RRM or CF over the multi-trait

4. Conclusions approach in terms of goodness of fit and computing