Genetic trends for milk yield in a flock of Saanen goats in Mexico

Milk production records (1413) of 566 Saanen goats by 29 sires from a flock from Querétaro, Mexico, were analysed to estimate genetic and phenotypic trends for the period 1991-1997. Best linear unbiased prediction methodology with an animal model was used to obtain predicted breeding values (PBV). Model included year-season of kidding and age as fixed effects and random animal additive and permanent environmental effects. The genetic trend was estimated for each sex as the regression coefficient of PBV means on year of birth, weighted by the number of animals in each year. Phenotypic trend was estimated using annual averages of first lactation milk yield on birth year weighted by the number of animals in each year. A strong connection across use of common sires allowed for unbiased estimation of genetic trends. The phenotypic trend was −37.75 ± 10.69 kg per year (P = 0.005). The genetic trend in males was −4.31 ± 3.68 kg per year (P = 0.27) and in females was −3.41 ± 1.31 kg per year (P = 0.02). Average number of daughters, reliability and PBV for 29 evaluated bucks were 19.5, 56.5% and −10.3 kg, respectively. Negative trends found in this study were probably due to ineffective selection of sires of external origin. Within-flock selection of males and females on their PBV is proposed as a more effective strategy for improvement for milk production in Mexican goat populations.