Impact of bovine neosporosis on reproductive performance of Girolando cows from a closed herd in Brazil.

Abstract

Bovine neosporosis, caused by Neospora caninum, is a major cause of reproductive disorders and economic loss in dairy cattle worldwide. This study evaluated the association between N. caninum serostatus and reproductive performance in Girolando cows in a closed herd in Valença, Rio de Janeiro, Brazil. A total of 144 cows were analyzed between September 2023 and April 2024. Blood samples were collected and tested for N. caninum antibodies using ELISA and confirmed by an indirect fluorescent antibody test (IFAT). Reproductive indices, including the number of services per conception, service period, calving interval, reproductive efficiency, conception rates at first and second services, pregnancy rate within two services, pregnancy rate at 150 days in lactation, and abortion rate, were evaluated over a four-year period in multiparous cows. ELISA screening of a subset of 49 animals revealed a seroprevalence of 44.9%, whereas IFAT confirmed that 29.9% of the total herds were seropositive. Seropositive cows required more services per conception (2.7 ± 0.2 vs. 2.1 ± 0.08; P = 0.05) and had a longer service period (142.3 ± 11.5 vs. 107.9 ± 4.8 days; P = 0.01) compared to seronegative cows. Trends were observed for longer calving intervals (413.6 ± 10.1 vs. 387.7 ± 5.5 days; P = 0.07) and reduced reproductive efficiency (91.2% vs. 96.1%; P = 0.07) in seropositive animals. Conception rates at the second service and pregnancy rates within the two services were higher in seronegative cows (60.3% vs. 42.4%, P = 0.04; 76.4% vs. 61.2%, P = 0.02, respectively). No significant differences were observed in first-service conception, pregnancy rate at 150 d of lactation, or abortion rate. Abortion occurred primarily around mid-gestation (mean 148 days). Our findings indicate that seropositivity for N. caninum is associated with poorer reproductive performance in Girolando cows by increasing service per conception and prolonging the service period, ultimately reducing herd efficiency. Although abortion rates were not significantly different, management practices and multifactorial causes likely influenced the outcomes. This study provides herd-level evidence on the association between N. caninum infection and reproductive performance in Girolando cows and underscores the importance of monitoring and controlling neosporosis to support reproductive management in dairy herds. Future research should prioritize vaccine development, effective therapies, and management strategies to mitigate the economic and reproductive effects of neosporosis.