Early-onset immune response to Haemonchus contortus infection in resistant Santa Ines suckling lambs compared with susceptible Ile de France

Santa Ines, an indigenous Brazilian hair sheep, in comparison with European sheep breeds (e.g., Ile de France), show greater resistance against gastrointestinal nematode (GIN) infections, mainly to Haemonchus contortus. Here we bring novel findings that address some gaps regarding the resistance traits involved in the development of the immunity of young lambs in the first few weeks of life to H. contortus infection. This study aimed to compare parasitological, humoral, and local effector cell-mediated responses, also the histopathological differences in the abomasal mucosa of Santa Ines (SI) and Ile de France (IF) suckling lambs serially infected with H. contortus. Parasitological variables, local and circulating humoral immunity, and local cellular response were evaluated in naïve Santa Ines (n = 14) and Ile de France (n = 12) lambs, randomized into four groups: infected SI (n = 8), non-infected control SI (n = 6), infected IF (n = 8) and non-infected control IF (n = 4). Lambs from infected groups were first infected at 14 days old, and multiple infections were conducted every second day, until the age of 66 days old (52 days post first infection). In comparison with infected Ile de France, infected Santa Ines lambs had lower mean eggs per gram of faeces, lower total H. contortus worm burden, lower females’ length, greater abomasal lymph node weight, greater mucosal thickness in the fundus, and also higher counts of eosinophils in the fundus, and mast cells and globule leukocytes in both fundic and pyloric mucosa of the abomasum. Intrabreed differences were observed into the infected Santa Ines group, with three of the eight lambs classified as highly resistant for displaying H. contortus burden ranging only from 1 to 42 worms. Overall, Santa Ines suckling lambs showed great resistance against H. contortus infection in comparison with Ile de France lambs, being able to mount a robust innate immune response at an early age, and before weaning. [Display omitted] •Resistance traits vary according to the sheep breeds and among individuals.•Santa Ines lambs showed a very robust innate immune response against H. contortus.•Resistant lambs were identified at an early age, and before weaning.•Stronger immunity resulted in reduced FEC and lower worm burden.•Early cellular immune response associated with worm clearance in hair breed.