Lamb Mortality, Gastrointestinal Helminth Infections and Associated Risk Factors in Smallholder

<title>Abstract</title> <p> Background Sheep production is an important source of livelihood for smallholder farmers in Ethiopia; however, high lamb mortality continues to limit flock productivity, household income, and food security. Integrated information on lamb mortality, gastrointestinal helminth infections, and associated risk factors remains limited in many sheep-producing areas. Objectives This study investigated lamb morbidity and mortality, major production constraints, gastrointestinal helminth infections, and factors associated with lamb mortality in selected districts of Southwest Shoa and Jimma Zones, Ethiopia. Methods A retrospective cohort study (May 2025–April 2026) was combined with a cross-sectional parasitological survey (January–April 2026). A total of 126 sheep-owning households and 430 lambs were included using multistage cluster sampling. Data were collected through household interviews, flock monitoring, and fecal examination using flotation and sedimentation techniques. Descriptive statistics and multilevel mixed-effects logistic regression were used for data analysis. Results The overall lamb morbidity and mortality rates were 23.95% and 14.65%, respectively, while the abortion and stillbirth rate was 24.88%. Disease was the leading production constraint, followed by predation, nutritional deficiency, starvation, and birth-related trauma. Among sick lambs, 41.7% received no treatment and only 39.8% were treated by animal health professionals. Lamb mortality was significantly associated with age, season, delayed colostrum intake (&gt; 6 h after birth), and birth type (P &lt; 0.05). Gastrointestinal helminths were detected in 58.84% of lambs. Strongyle-type nematodes were the predominant parasites (37.15%), followed by <italic>Moniezia expansa</italic> (22.13%), mixed infections (18.97%), <italic>Fasciola</italic> spp. (10.67%), <italic>Paramphistomum</italic> spp. (5.93%), <italic>Trichuris ovis</italic> (2.76%), and <italic>Nematodirus</italic> spp. (2.37%). Infection with <italic>Fasciola</italic> spp. was independently associated with increased lamb mortality (P &lt; 0.05). Conclusions Lamb mortality remains a major constraint to sheep production in the study areas. Improved neonatal care, timely colostrum feeding, strengthened veterinary services, and strategic helminth control are recommended to improve lamb survival and flock productivity. </p>