Impact of Neosporosis Sero-Positivity Status on Some Key Performance Indicators in Spring Calving Beef Cow Herds in Ireland

Neosporosis in cattle is caused by a coccidian parasite known as Neospora canium. This protozoan parasite can be spread vertically from the cow to the foetus during pregnancy, or horizontally through contamination of feed from faeces of infected canids. To-date, there is no published information on the sero-prevalence of neosporosis or its impact on reproductive and mortality traits in spring calving beef cow herds in Ireland. The objectives of this study were to quantify the effects, if any that neosporosis had on 12 week in-calf rate, calving interval, re-appearance rate and calf mortality (≤28 days). A total of 4344 cows from 134 spring calving beef cow herds across Ireland were blood sampled to measure the sero-prevalence of neopsorosis. All serum samples were tested for antibodies against Neospora canium using a commercially available diagnostic kit. All cows were ultrasonically scanned to determine pregnancy status at least 30 days after the end of the breeding season. Records for participating herds pertaining to calving interval and calf mortality were extracted from the Irish Cattle Breeding Federation database. Re-appearance rate was quantified as the percentage of cows that were scanned pregnant and calved in the following spring-calving season. Data were analysed using the generalised linear models procedure of SAS (version 9.3) with terms for herd, parity, cow breed, sire breed and animal movements included. The overall prevalence of neosporosis was 5.5% (238/4344). Overall herd pregnancy rate at the end of the breeding season was 89 (78-100%) and 88% (81-100%), for 2014 and 2015, respectively. There was no difference in 12 week in-calf rate (87.1 ± 0.9% vs 83.2 ± 2.5%; P = 0.13), calving interval (372.8 ± 1d vs 369.8 ± 2.9d; P = 0.13) and calf mortality up to 28 days of age (2.9 ± 0.4% vs 3.2 ± 1.4%; P = 0.87) between sero-negative and sero-positive cows respectively. However, re-appearance was significantly higher (89.6 ± 0.6 vs 82.4 ± 2.2%; P = 0.001) in sero-negative cows in comparison to their sero-positive compatriots. This was one of the largest studies of its kind to be carried out in beef cattle. The results indicate that there was a significant decrease in re-appearance rate in cows determined as sero-positive for neosporosis. This may be considered as a measure of foetal lose or abortion in these infected cows. However, there was no negative carryover relationship between neosporosis and other key economically important production indicators.