Immunological studies on new rabbit paternal lines with different potentials for growth rate and resilience: pathways towards healthier animals

This study evaluated leukocyte and immune parameters in female rabbits and their kits from three genetic lines (R, RF, and RFLP) during their first reproductive cycle. The R line was selected for growth rate over 37 generations, the RF line was derived from elite R animals, and the RFLP was obtained by backcrossing the RF line with a maternal line (LP). In females, the total lymphocyte percentage decreased from the first AI to weaning (-15.8 percentage points; p < 0.001; MIXED model); granulocytes peaked at weaning (+12.4 percentage points greater than the AI and +4.4 percentage points greater than parturition; p < 0.01; MIXED model). The CD4⁺ /CD8⁺ ratio increased 53.4% (p < 0.001; MIXED model), and the haptoglobin concentration doubled (p < 0.001; MIXED model). RF and RFLP had higher total lymphocyte percentages than R did (+6.4 and +4.6 percentage points; p < 0.05; MIXED model). R females had lower CD4⁺ percentages and CD4⁺ /CD8⁺ ratios than RLFP females did (-3.4 percentage points and -24.4%; p < 0.05; MIXED model) but higher monocyte and granulocyte percentages (on average +0.9 and +4.1 percentage points; p < 0.05; MIXED model). At weaning, R kits had fewer T lymphocytes and CD4⁺ T lymphocytes than RF kits did (-8.1 and -6.1 percentage points; p < 0.05; GLM) and lower CD25⁺ and phagocytosis of heterophils than RFLP kits did (-0.8 and -1.2 percentage points; p < 0.05; GLM). The results suggest that creating a paternal line via elite animals (RFs) and backcrossing it with a robust line could improve immune status and stayability, offering insights into the impacts of rabbit breeding on immune health and reproductive success.