Caracterização dos motivos de descarte e estimativas de parâmetros genéticos para longevidade de vacas da raça holandês

Abstract

The longevity of dairy cows directly impacts profitability and animal welfare, making it essential to identify culling reasons and estimate related genetic parameters. Analyzing culling reasons can improve management and selection in dairy cattle breeding programs. This study evaluated 34 culling reasons in Holstein dairy herds. Data from 3,096,872 Holstein cows culled in 9,683 Canadian herds between 1996 and 2020 were analyzed. The main culling reasons were reproductive problems (23.02%), followed by milk production (20.82%) and health issues (20.39%). About 58% of the cows were culled after 47 months of age. Economic-related culling frequencies were lower than expected until 2014 and higher between 2015 and 2020. Reproductive problems were predominant in fall, winter, and spring, while health issues prevailed in summer. In Quebec, health was the main culling reason, whereas in Ontario, milk production was the primary factor. Reproductive problems and milk production were the leading causes of culling in most ecozones, except in the Boreal Shield and Atlantic Maritime regions, where health issues predominated (25.12% and 23.75%, respectively). Genetic parameters for eight longevity indicators associated with age, functionality, economic factors, conformation, health, reproduction, production, and unknown reasons were estimated using random regression models (RRM) with fifth-order Legendre polynomials. Heritability estimates ranged from low to high, depending on age and culling reason: age-related (0.17–0.38), functionality (0.04–0.52), economic (0.002–0.20), conformation (0.02–0.28), production (0.02–0.26), health (0.02–0.25), reproduction (0.02–0.24), and unknown reasons (0.02–0.22). Genetic correlations were positive for nearby ages and negative for distant ages. Genetic trends indicated gains at younger ages and losses at older ages. These findings highlight the importance of considering culling reasons in breeding programs, enabling more efficient selection of Holstein cows for increased longevity and productivity.