Genetic and Environmental Sources of Variation of Milk Yield of Skopelos Dairy Goats

Small Ruminant Research 36 (2000) 1±5

Genetic and environmental sources of variation of milk yield of Skopelos dairy goats

A. Kominakisa,*, E. Rogdakisa, Ch. Vasiloudisb, O. Liaskosc

aDepartment of Animal Breeding and Husbandry, Faculty of Animal Science, Agricultural University of Athens, Iera Odos 75, 11855 Athens, Greece bAgricultural Development Service of Skopelos, Skopelos, Greece cCentre of Livestock Genetic Improvement, Karditsa, Greece

Accepted 8 August 1999

Abstract

Lactation records of the Skopelos dairy goat population were used to assess the importance of various environmental effects and to estimate genetic parameters for 90-day milk yield (9OMY) and total milk yield (TMY) on untransformed and on log scale. Average 9OMY, TMY and days of milking were 164.7, 239.2 kg and 187 days, respectively. Herd, production year, lambing month, birth type, lactation number, the herd by year, year by month, year by lactation number interactions and days of milking were found statistically signi®cant for TMY. Heritability estimates were 0.15 and 0.14 for 9OMY and TMY, respectively. Higher heritabilities of 0.24 and of 0.28 were estimated on the log scale for 90MY and TMY, respectively. Genetic and phenotypic correlations between 9OMY and total milk yield were found high, of 0.95 and 0.80, respectively. # 2000 Published by Elsevier Science B.V. All rights reserved.

Keywords: Goat; Milk yield; Heritability; Correlation

1. Introduction 10,000 animals. The animals are small bodied (68 cm height at withers) but exceptionally heavy (56 kg In the group of Aegean islands called the Northern for the adult females). The breed is characterized Sporades, east of the Magnisia continental region of by smooth glossy hair coat with dominating red Greece, a goat breed called the ``Skopelos goat'' brownish coloration. Both males and females are (deriving its name from the island of Skopelos) has horned (Pappas et al., 1992). The commercial average been known to have excellent productivity potential. milk yield of the recorded does was 258 kg in 1991 According to the local authority of the agricultural (Pappas et al., 1992) with an average of 263 kg during development service of the island of Skopelos the years 1986±1992 (Rogdakis et al., 1996). Fat content breed numbers in its area of origin around 8,000± of milk is reported exceptionally high (6.08%, Pappas et al., 1992; 5.6%, Rogdakis et al., 1996). Protein and lactose content is 4.0% and 4.6%, respectively. The * Corresponding author. Tel.: 30-1-5294403; fax: 30-1-5294442. proli®cacy is 1.4 kids per doe and year, the average E-mail address: [email protected] (A. Kominakis). birth weight of kids is 3.3 kg, while the kids' body

0921-4488/00/$ ± see front matter # 2000 Published by Elsevier Science B.V. All rights reserved. PII: S 0921-4488(99)00105-4 2 A. Kominakis et al. / Small Ruminant Research 36 (2000) 1±5 weight at the age of 59 days is 12.0 kg (Rogdakis et al., signi®cant linear correlation was detected between 1996). herd means and herd phenotypic standard deviations Reliable and speci®c population parameter esti- (SD) for untransformed data (r 0.66, p < 0.001). mates of heritabilities and genetic correlations of Log transformation was employed in an attempt to production traits are essential in predicting breeding adjust for heterogenous variance across herds. values accurately as well as in developing ef®cient breeding schemes. For dairy goats, a number of 2.2. Test of signi®cance of environmental effects genetic parameter estimates have been reported in the past for milk yield, based on paternal half-sib The mathematical model for 90MY included: herd, correlations (Bouillon and Ricordeau, 1975; Steine, year, month, birth type, lactation number and the herd 1976; Roenningen, 1980; Mavrogenis et al., 1984; by year, year by month and lactation by year interac- Sullivan et al., 1986; Constantinou, 1989; Mavrogenis tions. Analysis of TMY included, apart from the above et al., 1989; Kala and Prakash, 1990) on dam-daughter environmental effects, days of milking as a linear and regression (Constantinou et al., 1985; Rabasco et al., quadratic covariate. The signi®cance of the various 1993) on the MINQUE method (Kennedy et al., 1982) environmental effects was determined by least squares or on the REML method (Boichard et al., 1989; analysis of variance (SAS, 1996). Bishop et al., 1994; Andonov et al., 1998). The aim of this study was to assess the importance 2.3. Parameter estimation of various environmental factors and to estimate genetic parameters for milk yield in the Skopelos Genetic parameters for 9OMY and TMY were breed using an animal model on untransformed and estimated by bivariate analysis applying an animal transformed data. model with animals' additive genetic effect as the only random effect. The (co)variance structure for this analysis can be described as 2. Materials and methods P V a A PA V e I; 2.1. Data E where a is the vector of the animals'P direct effects, e Lactation records (n 24,420) for milk yield from the vector of residual errors, the q Â q matrix of A P 4962 does recorded during years 1988±1997 were additive genetic covariances s ; the matrix of Aij E collected from the center of livestock genetic improve- error covariances s , A the numerator relationship Eij ment located at Karditsa in Central Greece. Initial data matrix between animals, I the identity matrix with edits involved dam number, herd code, production order of the number of records and * denotes the direct year, lambing month, lactation number, birth type matrix product. All remaining covariances were (single, twin), days in milk, 90-day milk yield assumed to be zero. The ®xed effects part of the model (90MY) and total milk yield (TMY). A total of included the effects found statistically signi®cant for 4990 records were excluded from the initial data set the two traits in the previous test. (Co)variance com- according to the following criteria: milk yield less than ponents as well as standard errors of estimates were 110 kg or higher than 730 kg; days of milking less estimated by a derivate-free algorithm using the than 110. The records retained were 19,430 lactations DFREML computer program (Meyer, 1997). from 4802 does (data set 1). Five month lambing classes, January, February, October, November and December, and six lactation number classes, 1±6, were 3. Results built. A smaller data set (no. 2) with pedigree infor- mation was used for estimation of genetic parameters. 3.1. Descriptive statistics This data included 1251 lactation records from 1029 does. The number of sires and dams with progeny Estimates of means and CVs for 9OMY, TMY records were 56 and 130, respectively. A statistically and days of milking for data set 1 and data 2 are A. Kominakis et al. / Small Ruminant Research 36 (2000) 1±5 3

Table 1 3.3. Genetic parameters Mean (x) and coef®cient of variation (CV%) for 90MY, TMY and days in milk in the Skopelos goat Table 2 presents the variance components, herit- Trait x (ÆS.E.) CV (%) abilities, genetic and phenotypic correlations for 9OMY (kg) 9OMY and TMY. To facilitate a comparison on the Set 1 164.7 Æ 0.4 32.2 linear and log scales, variance component estimates of Set 2 155.7 Æ 1.3 29.5 log scale are multiplied by 105. The heritability esti- TMY (kg) mates for untransformed data for 9OMY and TMY Set 1 239.2 Æ 0.7 38.9 were 0.15 and 0.14, respectively. Log transformation Set 2 224.2 Æ 2.4 38.6 Days of milking of the data did not signi®cantly change the additive Set 1 187 Æ 0.3 21.1 genetic variances for 9OMY but reduced that of TMY. Set 2 167 Æ 1.0 20.4 Most evident was the reduction in residual and there- fore in phenotypic variances. As a result, higher heritabilities of 0.24 and of 0.28, after log transformation, were estimated for 9OMY and TMY, respec- summarized in Table 1. 9OMY, TMY and days of tively. Genetic correlation between 9OMY and milk milking were 164.7, 239.2 kg and 187 days for data set yield (MY) was found to be 0.95 and 0.93 for untrans- 1 and 155.7, 224.2 kg and 167 days for data set 2. formed and transformed records, respectively. Pheno- Furthermore, log transformation of data resulted in a typic correlation was estimated of 0.80 and 0.78 on the non-signi®cant correlation (r 0.09) between herd untransformed and on the log scale, respectively. means and herd phenotypic SD.

4. Discussion 3.2. Environmental effects 4.1. Environmental effects Herd, production year, lambing month, birth type, lactation number and the herd by year, year by month The importance of the various environmental and year by lactation number interactions were found effects on milk yield has been also examined in other to be statistically signi®cant for 9OMY and TMY in studies. Mavrogenis et al. (1984) found that year of data set 1. In data set 2 all the main effects and only the kidding, month of kidding, age of the goat and the year herd by year interaction were signi®cant for 9OMY by month interaction had a signi®cant effect on milk and TMY. Days of milking were found statistically yield of Damascus goats in Cyprus. In a later study, signi®cant as a quadratic covariate for TMY in both Mavrogenis et al. (1989) noted the importance of herd, data sets. season of kidding, season by year interaction and the

Table 2 Estimates of variance components, heritabilities, genetic and phenotypic correlations for 9OMY and TMYa

9OMY TMY

NT (kg2) LT (105 Â kg2) NT (kg2) LT (105 Â kg2)

2 sa 107.12 102 185.08 117 2 se 597.66 322 1136.64 299 2 sp 704.78 424 1321.72 416 h2 (ÆS.E.) 0.15 Æ 0.04 0.24 Æ 0.04 0.14 Æ 0.04 0.28 Æ 0.04 r (ÆS.E.) 0.95 Æ 0.13 0.93 Æ 0.13 A12 r 0.80 0.78 P12 a 2 2 2 2 NT: non-transformed data; LT: log transformed data. sa : additive genetic variance; se : error variance; sp: phenotypic variance; h : heritability; r : genetic correlation; r : phenotypic correlation. A12 P12 4 A. Kominakis et al. / Small Ruminant Research 36 (2000) 1±5 lactation number on milk yield of Damascus goats. Rabasco et al., 1993). Estimates by the REML method Boichard et al. (1989) reported that month within year, ranged from 0.29 to 0.31 (Boichard et al., 1989; age at kidding and birth type signi®cantly affected Bishop et al., 1994; Andonov et al., 1998). Literature milk yield of Alpine and Saanen goats. Kala and estimates of 9OMY were in the range of 0.29±0.52 Prakash (1990) found that year and season of lambing (Mavrogenis et al., 1984, 1989; Constantinou et al., accounted for variation of milk yield in two Indian 1985; Constantinou, 1989). Genetic correlations goat breeds while Rabasco et al. (1993) found that between 9OMY and TMY were very high. These production year, lactation number and birth type but estimates are agreement with other studies (Mavro- not herd, were signi®cant effects for milk yield in the genis et al., 1984, 1989; Constantinou et al., 1985; Spanish Verata goats. Constantinou, 1989). The present ®ndings suggest that genetic variability 4.2. Parameter estimates in milk yield is adequate for selection provided that herd variation has been accounted for. Selecting on the Herd means were found not to be correlated to herd basis of part lactation records is probably as ef®cient, phenotypic SD after log transformation. Transforming in view of the very high and positive genetic correla- records to algorithms was thus an appropriate method tions between 9OMY and TMY. 9OMY as a trait to to equalizing variances across herds implying that select for, appears to be more advantageous because it heterogeneity of variance was just a scale effect. is standardized for lactation length, is obtained on a Estimated variances on the untransformed scale, much shorter time interval and can be recorded with expressed as a coef®cient of variation (CV), was reduced costs than total milk yield. Attention, how-

0.063 and 0.056 for genetic effects (sA/my) and ever, should be paid when selection is practiced on 0.148 and 0.140 for residual effects (se/my) for milk yield because of the negative genetic correlations 9OMY and TMY, respectively. CV on the log scale between milk yield and fat content and milk yield and was 0.061 and 0.045 for genetic effects and 0.109 and protein content (Bouillon and Ricordeau, 1975; Boi- 0.072 for residual effects of 9OMY and TMY, respec- chard et al., 1989; Kala and Prakash, 1990; Andonov tively. Thus, log transformation resulted in reduction et al., 1998). Selection on milk yield would result in of genetic but in proportionally higher decreases in loss of protein and fat contents with a negative impact residual variances. As a result higher heritability on quality of various dairy products (goat cheese and estimates for 9OMY and TMY were obtained when yogurt). An answer to this problem might be selecting compared to the untransformed scale. Higher herit- the breeding animals for fat yield or attempting to abilities for log yields have been also reported in dairy introduce independent culling levels for milk yield and cattle (Hill et al., 1983; De Veer and Van Vleck, 1987). milk contents (Kominakis et al., 1998). Genetic variance components are also found to be related to the mean although this relationship has not 5. Conclusion been consistent (Hill et al., 1983; Lofgren et al., 1985; Mirande and Van Vleck, 1985). Employment of log transformation on milk yield Heritability estimates for TMY obtained from records in an attempt to adjust for heterogenous herd untransformed records were lower but those obtained variation resulted in higher heritability estimates for after transformation were comparable to those milk yield in Skopelos dairy goats. TMY and 90MY reported in the literature. Early literature reviews of have similar heritabilities and are genetically highly heritabilities of milk yield in dairy goats (Iloeje and correlated. Thus, the latter could be used as an alter- Van Vleck, 1978; Shelton, 1978) reported estimates native selection criterion. ranging from 0.16 to 0.60 with an unweighted mean value of 0.32. Later references reported heritabilities References of milk yield in the range of 0.18±0.32 (Kennedy et al., 1982; Mavrogenis et al., 1984; Constantinou et al., Andonov, S., Kovac, M., Kompan, D., Dzabirski, V., 1998. Estimation of covariance components for test day production 1985; Sullivan et al., 1986; Constantinou, 1989; in dairy goat, Proceedings of 6th World Cong. Genet. Appl. Mavrogenis et al., 1989; Kala and Prakash, 1990; Livest. Prod., 24, pp. 145±148 A. Kominakis et al. / Small Ruminant Research 36 (2000) 1±5 5

Bishop, S., Sullivan, B., Schaeffer, L.R., 1994. Genetic evaluation Lofgren, D.L., Vinson, W.E., Pearson, R.E., Powell, R.L., 1985. of Canadian dairy goats using test-day data. In: Lajoie, L., Heritability of milk yield at different herd means and variances Lafontaine, S., Doyle, P. (Eds.), Milk and Beef Recording State for production. J. Dairy Sci. 68, 2737±2739. of the Art, Proceedings of the 29th Biennial Session of the Mavrogenis, A.P., Constantinou, A., Louca, A., 1984. Environ- International Committee for Animal Recording, Ottawa, mental and genetic causes of variation in production traits of Canada, pp. 299±302. Damascus goats. 2. Goat productivity. Anim. Prod. 38, 99±104. Boichard, D., Bouloc, N., Ricordeau, G., Piacere, A., Barillet, F., Mavrogenis, A., Papachristoforou, C., Lysandrides, P., Roushias, 1989. Genetic parameters for ®rst lactation dairy traits in the A., 1989. Environmental and genetic effects of udder Alpine and Saanen goat breeds. Genet. Sel. Evol. 21, 205±215. characteristics and milk production in Damascus goats. Small Bouillon, J., Ricordeau, G., 1975. Parameters genetiques des Rumin. Res. 2, 333±343. performances de croissance et de production laitiere les caprins Meyer, K., 1997. DFREML. User Notes, ver. 3.0, Anim. Genet. Breed. en station de testage. 1res Journees de la Recherche Ovine et Unit, University of New England, Armidale, Australia. Caprine, pp. 124±132. Mirande, S.L., Van Vleck, L.D., 1985. Trends in genetic and Constantinou, A., Beuing, R., Mavrogenis, A.P., 1985. Genetic and phenotypic variances for milk production. J. Dairy Sci. 68, phenotypic parameters for some reproduction and milk 2278±2286. production characters of the Damascus goat. Z. Tierzuechtg. Pappas, B., Boyazoglou, J., Vasiloudis, Ch., 1992. The Skopelos Zuechtgsbiol. 102, 301±307. goat breed of Greece. AGRI (FAO) 9, 79±86. Constantinou, A., 1989. Genetic and environmental relationships of Rabasco, A., Serradilla, J.M., Padilla, J.A., Serrano, A., 1993. body weight, milk yield and litter size in Damascus goats. Genetic and non-genetic sources of variation in yield and Small Rumin. Res. 2, 163±174. composition of milk in Verata goats. Small Rumin. Res. 11, De Veer, J.C., Van Vleck, L.D., 1987. Genetic parameters for ®rst 151±161. lactation milk yields at three levels of herd production. J. Dairy Roenningen, K., 1980. Expected genetic progress in milk yield in Sci. 70, 1434±1441. the goat, with special emphasis on Swedish conditions. Int. Hill, W.G., Edward, M.R., Ahmed, M.K.A., Thompson, R., 1983. Goat and Sheep Res. 1, 18±40. Heritability of milk yield and composition at different levels Rogdakis, E., Vasiloudis, Ch., Mitsoyiannis, D., Papadimitriou, T., and variability of production. Anim. Prod. 36, 59±68. Panopoulou, E., 1996. Skopelos milk goat: Morphological Iloeje, M.U., Van Vleck, L.D., 1978. Genetics of dairy gaots: a characteristics and productivity (in Greek with English review. J. Dairy Sci. 61, 1521±1528. abstract). Anim. Sci. Rev. 22, 25±35. Kala, S.N., Prakash, B., 1990. Genetic and phenotypic parameters SAS, 1996. User notes ver. 6.12, 4th ed. SAS Institute, Cary, NC. of milk yield and milk composition in two Indian goat breeds. Shelton, M., 1978. Reproduction and breeding of goats. J. Dairy Small Rumin. Res. 3, 475±484. Sci. 61, 994±1010. Kennedy, B.W., Finley, C.M., Bradford, G.E., 1982. Phenotypic Steine, T.A., 1976. Genetic and phenotypic parameters for and genetic relationships between reproduction and milk production traits in goat. Dep. of Anim. Genetics and Breeding, production in dairy goats. J. Dairy Sci. 65, 2373±2383. Agr. Univ. Norway Report No. 398, vol. 55 (4), pp. 19±23. Kominakis, A., Rogdakis, E., Koutsotolis, K., 1998. Genetic Sullivan, B.P., Kennedy, B.W., Schaeffer, L.R., 1986. Heritabilities, parameters for milk yield and litter size in Boutsico dairy repeatabilities, repeatabilities and correlations for milk, fat and sheep. Can. J. Anim. Sci. 78, 525±532. protein yields in goats (Abstract). J. Dairy Sci. 69, 100.