Genetic analysis of first lactation test day traits in Sahiwal cattle

Abstract

Records on first lactation test day traits pertaining to Sahiwal cattle maintained at ICAR-National Dairy Research Institute over a period of 29 years (1988-2016) were utilized in this study. Test day traits, viz. test day milk yields (TDMY), test day fat yields (TDFY) and test day solid not fat yields (TDSNFY) were recorded at monthly intervals and a total of 11 test days were included up to 305 days lactation. Effect of different genetic and non-genetic factors on test day traits was assessed using least-squares mixed model. Random effect of sire and fixed effect of period of calving as well as season of calving had significant effect on different test day traits, however, age group at first calving had no significant effect in the present study. Paternal half-sib correlation method was used to estimate the heritability of different test day traits. Heritability estimates as observed for different test day traits varied from low to high. Heritability for test day milk yields, test day fat yields and test day SNF yields ranged from 0.06 (TDMY8) to 0.40(TDMY2), 0.09 (TDFY11) to 0.62 (TDFY10) and 0.06 (TDSNFY5) to 0.44 (TDSNFY2), respectively. Highest heritability of test day milk yield and test day solid not fat yield in second test day suggested that this test day could be used as early selection criteria for these two traits.