A robust rabbit line increases leucocyte counts at weaning and reduces mortality by digestive disorder during fattening

The present work evaluates how a rabbit line selected for robustness and two other lines selected for productive criteria, could have affected the physiological maturity and blood leukocytes counts of young rabbits at weaning, as well as their possible effect on the subsequent performance and health status during the growing period. The study was conducted on a total of 2904 young rabbits weaned at 30 days, belonging to three different genetic types (line H, founded for litter size at birth and selected for litter size at weaning during 17 generations; line LP, characterised by robustness founded for reproductive longevity criteria and selected for litter size at weaning for 7 generations; and line R, founded and selected during 25 generations for average daily gain from the 4th to the 9th week of life). Two different diets were used during lactation. The two diets were both isoenergetic and isoprotein but their main energy source differed, being either animal fat (AF) or cereal starch (CS). Leucocyte subsets were characterised at weaning, and growing performance was studied until 58 days of age (feed intake, live weight, mortality by digestive disorders and morbidity) for both medicated and non-medicated dietary versions. At weaning, young rabbits fed an AF lactating diet evidenced greater B lymphocyte count (on av. +8.6 ± 3.5 × 10(6)/L; P < 0.05) than those fed a CS diet. With respect to H and R rabbits, blood from LP ones had higher counts for total (on av. 591 ± 167 × 10(6)/L; P < 0.05), B (on av. +11.05 ± 4.3 × 10(6)/L; P < 0.05), T CD5(+) (on av. +266 ± 83 × 10(6)/L; P < 0.05) and CD8(+) lymphocytes (on av. +72.5 ± 28 × 10(6)/L; P < 0.05), and with respect to R, higher counts of CD4(+) (on av. +121 ± 47 × 10(6)/L; P < 0.05) lymphocytes (on av. +12.3 ± 4.1 × 10(6)/L; P < 0.05), monocytes (on av. +66 ± 32 × 10(6)/L; P < 0.05) and granulocytes (on av. +567 ± 182 × 10(6)/L; P<0.05) at weaning. LP line rabbits also showed lower mortality by digestive disorders (on av. -8 points of percentage) and morbidity (on av. -4 points) than those from H and R lines during the growing period (P < 0.05). R animals presented higher feed intake and daily weight gain, and a lower feed conversion ratio than H and LP animals (on av. +16.7 ± 2.7 g dry matter/day, +10.3 ± 0.4 g/day and -0.22 ± 0.04 g dry matter/g, respectively). In conclusion, the foundation of a line for reproductive longevity, which has been previously reported to give greater robustness (low environmental sensitivity) to their reproductive stock, could have conferred higher leukocytes counts at weaning to their offspring, as well as a better ability to confront digestive disorders as compared to other lines founded or selected exclusively for productive criteria.