SELECTION FREE ESTIMATES OF GENETIC-PARAMETERS OF PRODUCTION AND REPRODUCTION TRAITS OF 1ST 3 LACTATIONS IN MURRAH BUFFALOS

A multitrait restricted maximum likelihood procedure was used for estimating sire and residual variance and covariance components among 13 production and reproduction traits in first 3 lactations of Murrah buffaloes. The data set comprised 716 first, 567 second and 237 third lactation records of Murrah buffaloes maintained at 2 military dairy farms and 2 state government farms. Traits studied were age at first calving and 4 traits (milk yield, lactation length, service and intercalving periods) per lactation for the first 3 lactations. The method considered all 13 traits simultaneously, and accounted for the bias in later lactation records due to selection on dairy performance. The heritability of age at first calving was 0.24+/-0.16. Heritabilities for the first 3 lactations were respectively 0.28+/-0.15,0.24+/-0.14 and 0.21+/-0.15 for milk yield; 0.15+/-0.11, 0.19+/-0.14 and 0.22+/-0.17 for lactation length. Heritabilities for service period ranged between 0.06 and 0.11 and for intercalving period between 0.05 and 0.12. The genetic correlations of age at first calving with milk yield in first 3 lactations were -0.47+/-0.33,-0.38+/-0.37 and -0.34+/-0.43. The moderate to high heritability of milk yield and the negative genetic correlation between age at first calving and milk yield indicated that selection for increased milk yield would reduce the age at first calving. Genetic and phenotypic correlations between milk yield and lactation length were large and positive in all the 3 lactations. Milk yield had very poor genetic association with service and intercalving periods. Genetic correlations for milk yield between lactations 1 and 2, 1 and 3, and 2 and 3, respectively, were 0.64+/-0.23, 0.53+/-0.32 and 0.59+/-0.32. Repeatabilities for milk yield in different lactations ranged from 0.43 to 0.52. Genetic and phenotypic correlations between production and reproduction in subsequent lactations, and between reproduction and subsequent lactation production were close to zero.