Milk yield test-day records on the first three lactations of 25,500 Holstein cows were used to estimate genetic parameters and predict breeding values for nine measures of persistency and 305-d milk yield in a random regression animal model using two criteria to define the fixed regression. Legendre polynomials of fourth and fifth orders were used to model the fixed and random regressions of lactation curves. The fixed regressions were adjusted for average milk yield on populations (single) or subpopulations (multiple) […]

Records of test-day milk yields of the first three lactations of 25,500 Holstein cows were used to estimate genetic parameters for milk yield by using two alternatives of definition of fixed regression of the random regression models (RRM). Legendre polynomials of fourth and fifth orders were used to model regression of fixed curve (defined based on averages of the populations or multiple sub-populations formed by grouping animals which calved at the same age and in the same season of the […]

A total of 87,045 milk yield records of 11,023 first-parity Holstein cows was utilized, obtained from 1997 to 2001 from different herds of 10 Minas Gerais locations. Six types of persistency measures in lactation were evaluated using milk yield breeding values, obtained by means of Random Regression Model – RRM. The Wilmink function was used to describe the random and fixed effects by RRM. Heritability estimates and genetic correlations for various persistency measures in lactation were dependent on the definition […]