DAIRY HERD GENETIC DIFFERENCES FOR LACTATION PRODUCTION

Genetic and Phenotypic Parameters for Milk Production Traits in the First and Second Lactation in Romanian Simmental Dairy Cows

The aim of the present study was to estimate genetic and phenotypic parameters of milk production traits in the first and second lactations of Romanian Simmental dairy cattle. For the estimation of variance, heritability, genetic and phenotypic correlations among milk yield, fat yield, protein yield, and percentages of fat and protein, 3400 first and second lactation records over a period of fi...

Genetic parameters for first lactation milk yields at three levels of herd production.

A multivariate linear model was used to estimate sire variance and covariance components and residual variance components for first lactation milk yield and logarithms of yield at three herd production levels using Restricted Maximum Likelihood with the Expectation-Maximization algorithm. Data for four separate analyses were 305-d, mature equivalent first lactation milk records from cows sired ...

Estimation of Genetic Parameters for Lactation Curve Traits in Holstein Dairy Cows in Iran

The objectives were to estimate (co)variance components and genetic parameters for lactation curve traits in Holstein dairy cows in Iran. The used data were records on Holstein cows collected during January 2003 to December 2012 by the Animal Breeding Center of Iran (Karaj, Iran). In order to describe the lactation curve, an incomplete gamma function was fitted to 691200 test-day records on 962...

Genetic covariances among relatives for dairy lactation records.

Genetic Analysis of Herd Life in Canadian Dairy Cattle on a Lactation Basis Using the Survival Kit

Longevity is a highly desirable trait that considerably affects overall profitability. With increased longevity the mean production of the herd increases because a greater proportion of the culling decisions are based on production and the proportion of mature cows, which produce more milk than young, cows is increased. An increased longevity enables higher selection intensity of females and th...