OPTIMIZATION OF AGE AT FIRST CALVING IN KARAN FRIES CATTLE

Data on 571 Karan Fries (crossing Tharparkar and Sahiwal cows with American Holstein Friesian sires) at NDRI, Karnal was studied for determination of optimum age at first calving (AFC). Least squares analysis (Harvey, 1975) was used to see the effect of sire, period and season of calving and was corrected for significant effect of non-genetic factors. The genetic and phenotypic parameters was estimated for the sires which had five or more progenies. The relationship between age at first calving with other traits were studied by using regression analysis and class interval method. The least squaqres means of age at first calving (AFC), first lactation 305 days or less milk yield (FL305Y), first lactation total milk yield (FLTMY), milk yield per day of first lactation length (MY/FLL) and milk yield per day of first calving interval (MY/FCI) was estimated as 940.98 ± 44.24 days, 3199+ 44.24 kgs, 3599.06 ± 54.96 kgs, 10.50 ± 0.14 kgs and 7.52 ± 0.26 kgs , respectively. The heritability estimates of these traits were moderate. The AFC had significant and positive phenotypic correlation with FL305Y, FLTMY, MY/FLL and MY/FCI. The genetic correlation of AFC with FLTMY was positive. Relationship between AFC and first lactation production traits could not be explained through regression analysis therefore class interval method was used to find at the relationship. Eight classes of AFC was used to find out the relationship. Optimum AFC was identified based on higher milk production and numbers of animals in various classes as 26-36 months. To determine the optimum range of AFC, much emphasis should be given as maximum profit rather than maximizing milk production.