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Staphylococcal mastitis is a major health problem in humans and livestock that leads to economic loss running in millions. This process is currently one of the main reasons for culling adult rabbit does. Surprisingly, the two most prevalent S. aureus lineages isolated from non-differentiable natural clinical mastitis in rabbits (ST121 and ST96) generate different immune responses. This study aimed to genetically compare both types of strains to search for possible dissimilarities to explain differences in immune response, and to check whether they showed similar virulence in in vitro tests as in experimental intramammary in vivo infection. The main differences were observed in the enterotoxin gene cluster (egc) and the immune-evasion-cluster (IEC) genes. While isolate ST121 harboured all six egc cluster members (seg, sei, selm, seln, selo, selu), isolate ST96 lacked the egc cluster. Strain ST96 carried a phage integrase Sa3 (Sa3int), compatible with a phage integrated into the hlb gene (β-haemolysin-converting bacteriophages) with IEC type F, while isolate ST121 lacked IEC genes and the hlb gene was intact. Moreover, the in vitro tests confirmed a different virulence capacity between strains as ST121 showed greater cytotoxicity for erythrocytes, polymorphonuclear leukocytes and macrophages than strain ST96. Differences were also found 7 days after experimental intramammary infection with 100 colony-forming units. The animals inoculated with strain ST121 developed more severe gross and histological mastitis, higher counts of macrophages in tissue and of all the cell populations in peripheral blood, and a significantly larger total number of bacteria than those infected by strain ST96.

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

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Genetic selection and nutrition management have played a central role in the development of commercial rabbitry industry over the last few decades, being able to affect productive and immunological traits of the animals. However, the implication of different energy sources in animals from diverse genetic lines achieving such evolutionary success remains still unknown. Therefore, in this work, 203 female rabbits housed and bred in the same conditions were used from their first artificial insemination until their fifth weaning. The animals belonged to three different genetic types diverging greatly on breeding goals (H line, hyper-prolific (n=66); LP line, robust (n=67) and R line, selected for growth rate (n=67), and were assigned to two experimental diets, promoting major differences in energy source (cereal starch or animal fat)). The aims of this work were to: (1) characterize and describe blood leucocyte populations of three lines of rabbit does in different physiological stages during their reproductive period: first artificial insemination, first weaning, second parturition and fifth weaning; and (2) study the possible influence of two different experimental diets on the leucocyte populations in peripheral blood. Flow cytometry analyses were performed on blood samples taken from females at each different sampling stade. Lymphocyte populations at both weanings were characterized by significantly lower counts of total, CD5+ and CD8+ lymphocytes (-19.8, -21.7 and -44.6%; P<0.05), and higher counts of monocytes and granulocytes (+49.2 and +26.2%; P<0.05) than in the other stages. Females had higher blood counts of lymphocytes B, CD8+ and CD25+ and lower counts of CD4+ at first than at fifth weaning (+55.6, +85.8, +57.5, -14.5%; P<0.05). G/L ratio was higher at both weanings (P<0.05), and CD4+/CD8+ ratio increased progressively from the 1AI to the 5 W (P<0.001). Regarding the effect of genetic type in blood leucocyte counts, LP animals presented the highest counts for total, B, CD5+ and CD8+ lymphocytes (+16.7, +31.8, +24.5 and +38.7; P<0.05), but R rabbits showed the highest counts for monocytes and granulocytes (+25.3 and +27.6; P<0.05). The type of diet given during the reproductive life did not affect the leucocyte population counts. These results indicate that there are detectable variations in the leucocyte profile depending on the reproductive stage of the animal (parturition, weaning or none of them). Moreover, foundation for reproductive longevity criteria allows animals to be more capable of adapting to the challenges of the reproductive cycle from an immunological viewpoint.

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or dviana@ uchceu.es.Despite the enormous efforts made to achieve effective tools that fight against Staphylococcus aureus, the results have not been successful. This failure may be due to the absence of truly representative experimental models. To overcome this deficiency, the present work describes and immunologically characterizes the infection for 28 days, in an experimental low-dose (300 colony-forming units) intradermal model of infection in rabbits, which reproduces the characteristic staphylococcal abscess. Surprisingly, when mutant strains in the genes involved in virulence (JDagr, JDcoaDvwb, JDhla, and JDpsma) were inoculated, no strong effect on the severity of lesions was observed, unlike other models that use high doses of bacteria. The inoculation of a human rabbitized (FdltB r ) strain demonstrated its capacity to generate a similar inflammatory response to a wild-type rabbit strain and, therefore, validated this model for conducting these experimental studies with human strains. To conclude, this model proved reproducible and may be an option of choice to check both wild-type and mutant strains of different origins.

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