Genetic control of milk yield from lactations of different duration in Nili-Ravi buffaloes
Abstract. Data on 2704 lactations of 1093 Nili-Ravi buffaloes were used to see the genetic control of milk yield projected for lactation length using information on last recorded yield and average daily yield of the recorded lactation. Year and season of calving and their interaction significantly affected actual and predicted milk yield. Winter calvers had a higher mean (1364.5±31.63 kg) as compared to summer calvers (1299.4±30.28 kg). The milk yield adjusted to 308-days increased from first parity (1731.8±78.86 kg) to third parity (1919.6±64.56 kg) where after it declined gradually. Age at calving with in parity affected lactation milk yield significantly (P<.01). Lactation length had a significant effect on actual and adjusted lactation yields but the effect was much smaller in projected lactations. Repeatability of actual lactation milk yield was 0.46±0.02. Heritability of actual lactation milk yield from paternal half-sib correlation method was 0.244±0.057. Lactations adjusted to 308 days by simple linear regression had a similar heritability (0.243±0.057) but lactations adjusted using last record-day information had slightly better heritability estimate (0.295±0.063 to 0.314±0.065). Estimate improved as data set was restricted to include more completed. Results from Animal Model analysis indicated that overall heritability value for actual lactation milk yield was 9.1% while for 308-day lactation milk yield (adjusted by using last record-day and or average daily milk yield information), value was 10.7 to 12.0%. Extension of all lactation records with less than 305-days length to standard such as 305-days using last record-day and average daily milk yield information is suggested.