González-de-la-Vara, M., De Anda, F., Romano, M. C. 2023. Dead newborn calf affects behavior, cortisol, milk production, and reproductive performance in primiparous dairy cows. Journal of Veterinary Behavior 66, 20–28.

Little is known about the long-term effects of stillbirth on dairy cows. This study compared the behavior, serum and hair cortisol concentrations, production and quality of milk, and reproductive performance in primiparous dairy cows that delivered dead or live newborn calves. Forty-four Holstein cows housed in an earth-flooring corral (42.66 m2/cow) were studied for 90 days and classified into two groups: 29 cows with alive newborn calves (AC group) and 15 cows with dead newborn calves (DC group). On the first day of lactation and on the 30th, 60th, and 90th day, hair and serum cortisol concentrations were measured using radioimmunoassay as reliable stress indicators. Social, sexual, and maintenance behaviors were observed daily for 4 hours. Milk yield was measured three times a day in a milking parlor, and somatic cell counts were compared at 3 and 9 months of lactation. Milk quality and body condition were also recorded. Cows in the AC group spent more time lying, ruminating, and drinking than cows in the DC group, which received and exhibited significantly less aggression. No differences were observed between the groups in the proportion of time spent standing, walking, or eating. Serum and hair cortisol concentrations were significantly higher in DC cows than in AC cows on day 60 of lactation. No differences were observed in the body condition or reproductive performance. As expected, the milk quality was higher in AC cows than in DC cows. Our study shows that the delivery of dead newborn calves by primiparous cows has a clear negative effect on long-term behavior, hair and serum cortisol concentrations, and milk production. These findings highlight the role of delivery pathology in primiparous cows.