Estimation of genetic parameters for dairy traits and somatic cell score in the first 3 parities using a random regression test-day model in French Alpine goats

摘要

Lactation curve shape can affect an animal’s health,feed requirements, and milk production throughout theyear. We implemented a random regression model forthe genetic evaluation of lactation curve shapes of dairytraits in French Alpine goats for their first 3 parities.Milk, fat, and protein yields, fat and protein contents,somatic cell score, and fat/protein ratio were considered.The data consisted of test-day records from 49,849 firstlactation Alpine goats during their first 3 lactations.The reference model used a Legendre polynomial oforder 2 for each parity to describe the genetic and permanentenvironmental effects, and was compared witha model that combined the second and third parities.A rank reduction of the variance-covariance matrix wasalso performed using an eigenvalue decomposition foreach parity from the 2 models. Genetic parameters wereconsistent between the models tested. With a reductionto rank 2 and combining the second and third parities,the first 2 principal components correctly summarizedthe genetic variability of milk yield level and persistency,with a near-nil correlation between the 2, andwith a much shorter computation time than the referencemodel. A favorable correlation of +0.43 betweenmilk yield persistency and fat/protein ratio persistencyat the beginning of the lactation was found from buckestimated breeding values.