Estimation of genetic parameters for testday milk records in Holstein cows of Tehran province using the covariance function

Knowledge of genetic parameters for economic traits is of great importance as a successful breeding programme is to be planned. The main objective of this study was to estimate genetic parameters of testday milk records for Holstein cows of Tehran province.
The records were collected by the Animal Breeding Center during 1997-2009. Edition of the initial data set was carried out by Excel and Foxpro software. Days in milk and age at first calving were restricted to be 5-305 d and 18-36 months, respectively. The final data consisted of 122,850 testday milk records from 12,285 Holstein cows (with 10 records each) in 147 herds. Analysis of environmental factors was carried out using a linear mixed model. Production group, calving year, production season, sperm type, two-way interactions, covariables of the Wilmink's function, age of cow at recording, Hosltein gene percentage, and random effect of sire were included in the model. Genetic analysis of the data was carried out using the covariance function model based on orthogonal Legendre polynomials.
All factors included in the mixed linear model had significant effects on testday milk records (P The findings of the present research indicate that testday milk records over the lactation period are not an expression of a single trait and as a result genetic evaluation should be undertaken using random regression testday models.