Environmental and genetic variation in milk yield of native cattle and crosses with Brown Swiss in India.
Effects of year, season, parity, age, their two-way interactions, lactation length and calving interval on milk yield were investigated utilizing 9,086 lactation records collected from 1930 to 1975 from six breed groups kept in one herd at Karnal, India. The breed groups involved three native breeds (Sahiwal, Red Sindhi and Tharpakar) and three crossbreds with Brown Swiss (F1 crosses between Brown Swiss and three native breeds, inter se crosses, and 3/4 Brown Swiss). Breed, year, season, parity, age and all of the two-way interactions with the exception of breed X season and parity X season were important. Tharpakar produced more milk than Sahiwal and Red Sindhi by 232 and 204 kg. The milk production difference between Sahiwal and Red Sindhi was only 28 kg. The three crossbreds outproduced the purebreds by an average of 766 kg; however, differences in management could have favored crossbreds. Among the crossbreds, F1 crosses were superior. The linear and quadratic regressions on lactation length accounted for 28% of the variation in milk yield after year, season, parity, age and their interactions were absorbed. Calving interval and lactation length together accounted for 29%. Estimates of heritability, from paternal half-sib analyses, and repeatability of milk yield for Red Sindhi, Sahiwal and Tharpakar ranged from .10 to .30. Differences among heritability estimates from different parities were small when more than 500 records were involved.