<p>Smallholder large ruminant production in Lao People’s Democratic Republic (Laos) is characterised by low reproductive efficiency. To determine if common abortifacient bovid infectious diseases are involved, a serological investigation was conducted. Sera was collected
from stored and fresh cattle (<i>n =</i> 390) and buffalo (<i>n =</i> 130) samples from 2016–18 from,
and then examined for associations in a retrospective risk factor study of 71 herds. The sera
were assayed for antibodies to <i>Neospora caninum</i>, bovine viral diarrhoea virus (BVDV),
<i>Leptospira interrogans</i> serovar Hardjo and <i>Brucella abortus</i> using commercially available
enzyme-linked immunosorbent assay kits. These pathogens were detected in buffalo samples at 78.5% (95% CI 71.4–85.6), 0%, 2.3% (95% CI 0–4.9) and 0%, respectively, and in cattle at 4.4% (95% CI 2.4–6.4), 7.7% (95% CI 3.1–12.3), 12.8% (95% CI 9.5–16.1) and
0.26% (95% CI 0–0.8), respectively. Exposure of buffalo to <i>N. caninum</i> was positively associated with buffalo age, with a predicted seropositivity at birth of 52.8%, increasing to 97.2% by 12 years of age (<i>p =</i> 0.037). Exposure of cattle to <i>L. interrogans</i> serovar Hardjo was more
prevalent in females compared to males, was associated with higher titres of BVDV, and
was more prevalent in the wet season compared to the dry season. Exposure of cattle to
BVDV was more prevalent in males compared to females, the wet and dry seasons were
comparable, and was associated with rising antibody titres against <i>N. caninum</i> and <i>L. interrogans</i> serovar Hardjo. The risk factor survey identified that the probability of herds being <i>N. caninum</i> positive increased with farmer age, if farmers believed there were rodents on farm,
and if farmers weren’t aware that canids or rodents could contaminate bovid feed on their
farm. The probability of a herd being positive to <i>L. interrogans</i> serovar Hardjo increased on
farms where multiple cows shared the same bull, where farmers had lower husbandry
knowledge, and on farms that used water troughs. The probability of a herd being BVDV
seropositive increased with increasing herd size and increasing titres to <i>N. caninum</i>. The
benchmarking of bovid exposure to emerging abortifacient pathogens and identification of their risk factors potentially informs disease prevention strategies, supporting efforts to establish a biosecure beef supply for enhanced smallholder livestock productivity, public
health and food security in Laos and surrounding countries.</p>