Estimation of genetic parameters and evaluation of test-day milk production in sheep

Genetic parameters and breeding values were estimated based on 11 708 daily milk yields from 2255 lactations (1351 sheep, 19 different flocks) between the years 2004 and 2010. The pedigree covered 2334 individuals, including both the recorded animals and their known ancestors. The fixed effects were estimated by the least-squares method, while the genetic parameters were estimated by the REML method. The data were tested by 49 models, but on the basis of the coefficient-of-determination value and the significance of the effects, only 10 models were used for REML analysis. The most suitable model was chosen on the basis of the breeding values distribution and the heritability of daily milk production, which was estimated at 0.28. The fixed effects of the flock parity number, the flock test day, and the linear and quadratic coefficients of flock’s days-in-milk in the chosen model were all highly significant (P < 0.0001) for the test-day milk yield. The breeding values had a normal distribution and a standard deviation of 0.46 kg.