Prediction functions for persistent lactation yield in crossbred cattle

Abstract

Records (1221) spreading over a period of 18 years (1970-87), on 407 crossbred cows of 7 genetic groups with half (1 exotic breed) and 3/4 (2 exotic breeds) inheritance involving Holstein Friesian (F), Brown Swiss (B) and Jersey (J) crosses with Hariana (H) cows, were analysed. Data adjusted for significant effect of parity, period and season of calving were adjusted to step-wise regression. Persistency index PI₆ along with peak yield was obtained as best fit prediction of corresponding lactation yield with coefficient of determination ranging between 71.69 and 97.41 %. Incorporation of lactation at third step along with PIG and peak yield did not further improve the determination significantly except for first lactation length in BFH and FJH and second lactation in FH and FJH genetic groups. In these 4 cases lactation length had highest ,determination at first step of regression, increasing significantly with incorporation of PI₆ and peak yield at second and third step of regression. The contribution of several other measures of persistency by inclusion at second or third step of regression along with lactation length and peak yield resulted to total determination ranging from 27.03 to 34.81 % and thus may not be regarded as good fit. Thus, incorporation of PI6 with lactation length and peak yield was obtained as best fit for predicting lactation yield.