Abstract
Neonatal calf diarrhoea remains a significant cause of mortality in dairy calves, often involving multiple pathogens.This study aimed to investigate the interactions between coccidian and bacterial pathogens within the intestinal tissues of calves that succumbed to diarrhoea. Intestinal samples were collected from 43 calves during 17 outbreaks in the peri-urban areas of Ludhiana, Punjab. Histopathological examination revealed the presence of sexual and asexual forms of Eimeria spp. in five calves. Immunohistochemistry detected Escherichia coli, Clostridium perfringens, and Salmonella spp. antigens in association with coccidian stages. Notably, C. perfringens exhibited a greater affinity for all stages of coccidia, including oocysts, compared to Salmonella spp., while E. coli antigens were predominantly localized extracellularly.These findings suggest that bacterial pathogens interact with specific stages of the coccidian life cycle, potentially modulating pathogenicity and contributing to the severity of intestinal lesions observed in neonatal calf diarrhoea.