Effects of genotype, parity, season and their interactions on milk yield in crossbred dairy cattle.

The crossbred dairy cattle (CDC) have been gaining popularity in the tropical countries for their increased milk yield within a short period of time because of heterogenic additive gene action. Hence, we aimed to investigate whether genotype, parity, season and their interactions had any effect on average daily milk yield (ADMY) of the CDC in a dairy farm at Chattogram district, Bangladesh, for a period of 3 years from January 2016 to December 2019. Total 16,425 retrospective lactation records of 150 multiparous Sahiwal × Friesian (Sahiwal = 50%, HF = 50%), Local × Friesian (Local = 50%, HF = 50%) and Local × Friesian (Local = 25%, HF = 75%) CDC from the first to the third parities (50 for each parity) were collected from the farm records. The generalized linear model and principal component analysis identified substantial impacts of genotype, parity, season and their interactions on ADMY of the CDC. The herd level least squared ADMY was 11.22 ± 0.04 kg/days on a 305-days typical lactation period. The Sahiwal × Friesian CDC produced 7.2% and 5.5% more milk than the Local × Friesian and Local × Friesian respectively. The CDC produced maximum milk in the second parity, which was 7.8% and 0.34% more than the first and third parities. Similarly, the highest ADMY was recorded in the spring, which was 10.8%, 7.3% and 6.6% more than the fall, summer and winter respectively. It was concluded that the Sahiwal × Friesian crossbred produced maximum milk in the spring season at the second parity while other determinants remained constant. The changing patterns of milk yield in different genotype, parity and seasons provided scientific evidence for improving feeding strategy to optimize herd level milk yield of CDC in the commercial dairy farms under tropical perspective.