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

Abstract

The aim of this study was to determine how genetic type could affect the physiological 14 and immune status of commercial rabbits at weaning, as well as their performance and 15 health during the growing period. The study was conducted on a total of 2904 young 16 rabbits weaned at 30 days, belonging to three different genetic types (line H, founded for 17 litter size at birth and selected for litter size at weaning during 17 generations; line LP, 18 founded for reproductive longevity criteria and selected for litter size at weaning for 7 19 generations; and line R, founded and selected during 25 generations for average daily 20 gain from the 4 th to the 9 th week of life). Two different diets were used during lactation. 21The two diets were both isoenergetic and isoproteic but their main energy source differed, 22 being either animal fat (AF) or cereal starch (CS). Leukocyte subsets were characterised 23 at weaning, and growing performance was studied until 58 days of age (feed intake, live 24 weight, mortality by digestive disorders and morbidity) for both medicated and non-25 medicated dietary versions. At weaning, young rabbits fed an AF lactating diet evidenced 26 greater B lymphocyte count (+ 46%) than those fed a CS diet. Blood from LP rabbits had 27 higher counts for total B, T CD5 + and CD8 + lymphocytes with respect to H and R (on av. 28 +40, +57, +28, and +27%, respectively; P<0.05), and CD4 + lymphocytes, monocytes and 29 granulocytes with respect to R (on av. +24, +32 and +44%, respectively; P<0.05) at 30 weaning. LP line rabbits also showed lower mortality by digestive disorders (on av. −8 31 points of percentage) and morbidity (on av. −4 points) than those from H and R lines 32 during the growing period (P<0.05). R animals presented higher feed intake and daily 33 weight gain, and a lower feed conversion ratio than H and LP animals (on av. +16.7±2.7 34 g dry matter/day, +10.3±0.4 g/day and −0.22±0.04 g dry matter/g, respectively). In 35 conclusion, the foundation of a line for reproductive longevity, which has been previously 36 reported to give greater robustness (low environmental sensitivity) to their reproductive 37 3 stock, could have also conferred a greater immunological development at weaning to their 38 offspring, as well as a better ability to confront digestive disorders as compared to other 39 lines founded or selected exclusively for productive criteria. 40

Long-term implications of feed energy source in different genetic types of reproductive rabbit females. II. Immunologic status

“…This mechanism of adaptation may be suggested as one of the factors contributing to increase the robustness of these animals, which may consequently be likely to live longer, although longevity is not their criteria of selection. Our data reinforce the hypothesis that the animals from a line founded by screening for reproductive longevity (LP line), under normal favourable breeding conditions, develop a greater immunological ability to confront reproductive challenges and to confer animals a more robust nature (Ferrian et al, 2012;García-Quirós et al, 2014).…”

“…So, animals from these genetic lines have been considered more robust than the rest (García-Quirós et al, 2014), understanding the concept of robustness in farm animals as defined by Knap (2005): 'The ability to combine a high production potential with resilience to stressors, allowing for unproblematic expression of a high production potential in a wide variety of environmental conditions'. In fact, these animals are not only able to adapt to short-term challenges, but can also integrate their adaptations over time to adapt to longterm patterns (e.g.…”

“…Notwithstanding the evidenced impact of genetic selection on the robustness of the animal, it has also been suggested that the use of a fat-enriched lactation diet could contribute to improving the maturity of the immune system of young rabbits at weaning (García-Quirós et al, 2014) and, therefore, their general health status towards the growing period. In this conceptual framework, this is the second of three consecutive papers (see companion papers Arnau-Bonachera et al, 2017a and2017b) that were designed to provide a context in which animals from three different genetic types and fed with two distinct dietsbut housed and bred in the same conditions-could be systematically studied and compared throughout their reproductive life (from the first artificial insemination to the sixth parturition).…”

Inflammatory Correlated Response in Two Lines of Rabbit Selected Divergently for Litter Size Environmental Variability

“…Total leucocyte counts are involved in the immunity reaction and defence of the organism [19,20]. Susceptible rabbits to acute infections may have a decrease in WBC count [21,22]. On the other hand, basophils are essential for linking innate and adaptive immunity [23].…”

Resistance to infectious diseases is a heritable trait in rabbits1

“…In Spain, a robust rabbit line founded by rabbits of high reproductive longevity showed higher leukocyte counts and better ability to confront digestive disorders (García-Quirós et al, 2014). So breeding for general disease resistance could indeed enhance the immune response.…”