Abstract
<jats:p>Infectious gastrointestinal diseases in young livestock cause substantial economic losses in animal husbandry by reducing survival, impairing growth, and increasing treatment costs. Among these diseases, colibacillosis caused by pathogenic Escherichia coli remains one of the most important bacterial infections affecting neonatal and young piglets. In this regard, the development of safe and effective immunoprophylactic agents is a priority in veterinary medicine. The aim of this study was to evaluate the safety and immunological efficacy of a live vaccine developed from the attenuated Escherichia coli EM-43 strain under field conditions. The research was conducted in 2024–2025 on farms in the Almaty region with a history of colibacillosis outbreaks. A total of 1,370 pigs were included in the trial, comprising approximately 170 sows and more than 1,200 piglets. The immunogenicity of the vaccine was assessed using the hemagglutination test. Within 14–21 days after vaccination, the geometric mean antibody titer in sow sera increased significantly to 1:368–1:485 (P < 0.05), compared with pre-vaccination levels of 1:10–1:20. These findings indicate the development of a strong post-vaccination immune response. Clinical monitoring showed that vaccinated animals remained in satisfactory general condition throughout the observation period. No neurological signs or other systemic adverse reactions were recorded. Only mild local swelling, approximately 3–5 cm in diameter at the injection site, was observed, and it resolved spontaneously within 4–6 days. In farms where the vaccine was applied, no clinical signs of colibacillosis were detected in either sows or piglets, and no mortality associated with the disease was recorded. The results demonstrate that the live vaccine based on the E. coli EM-43 strain is highly immunogenic, safe, and suitable for practical use in pig farming as a reliable means of colibacillosis prevention.</jats:p>