Comparison of four methods of variance components estimation for heritability of economic traits in Murrah buffalo

Abstract

First lactation records on 2 107 Murrah buffaloes, maintained at 4 military dairy farms (Ambala, Ferozpur, Lucknow and Meerut) and 3 UP State Government Farms (Babugarh, Mathura and Madurikund) during 1961-88 were used to compare 4 methods of varjance components estimation viz. Henderson method-3 (H M-3), maximum likelihood (ML), restricted maximum likelihood (REML) and minimum variance quadratic unbiased estimation (MIVQUE). Traits included In the study were age at first calving, first lactation milk yield, first lactation length and first calving interval. Sire and residual variance components were estimated from a model containing season, and year of calving and farm as fixed effects and sires within farm as random effect. Sire variance components obtained from HM-3 and MIVQUE for all traits except first lactation milk yield were significantly (P<.05) different from sire variance components obtained from likelihood procedures. ML estimates of sire and error variance components were smaller than obtained from other procedures. Estimates of sire components of variance for first lactation length and first calving interval obtained from HM-3 and MIVQUE were negative. Likelihood estimation (REML and ML) procedures estimates confined to the parameter space. Heritability estimate for age at first calving obtained from HM-3 and MIVQUE procedures was moderate. The heritability estimate for first lactation milk yield obtained from HM-3 was highest (0.25±0.08). ML estimates of heritability for first lactation milk yield was lowest (0.21 ±0.07). The estimates of heritability for first lactation length obta;ned from M Land REML were almost of SImilar magnitude. Result revealed that likelihood mcthods always yield positive estimates of heritability and therefore should be the methods of choice over the fitting constants procedure (HM-3) for unbal,lIlced data in mixed modcls.