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

Abstract

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.

Long-term implications of feed energy source in different genetic types of reproductive rabbit females: I. Resource acquisition and allocation

“…It has been reported that fat-enriched diets favour milk yield, whereas starch-enriched diets favour body reserve gain (Pascual et al, 2003). This is the first of three consecutive scientific papers that aim to evaluate the hypothesis that the effect of energy source of the diet varies with the genetic type, having implications in the way each genetic type acquires and allocates resources over time, their immunological status or their fitness and productivity (see companion papers Arnau-Bonachera et al, 2017;Penadés et al, 2017). Specifically, in the present work we studied: (i) the way three genetic types, widely differing in their genetic background, acquire and allocate resources.…”

Long-term implications of feed energy source in different genetic types of reproductive rabbit females: III. Fitness and productivity

“…However, when fed with a diet promoting the restoration of body reserves (CS) they could become overfat, increasing the risk of not getting pregnant (Figure 3) or death ( Figure 5). Moreover, this situation could be especially risky if we consider that H females presented some symptoms of aging of their immune system at second parturition, which increased with age (Penadés et al, 2017). Therefore, despite the results from the first reproductive cycle, fitness traits of H females were globally more favoured when fed with AF compared to CS (Figure 3), not affecting mean productivity at sixth parturition.…”

“…Consequently, this point has been described as the moment with the highest risk for females to be removed from farms (Rosell and de la Fuente, 2009). However, at this point, LP females presented high values of blood glucose, low levels of NEFA and BOHB (Arnau-Bonachera et al, 2017) and higher counts of lymphocytes T and B (Penadés et al, 2017), which suggest a better metabolic and immunologic status at this point. Therefore, the main consequence of this low risk strategy would be the highest survival rate at second parturition of LP females ( Figure 2).…”

“…This way, they could safeguard body condition and reach critical points of their life trajectory in good metabolic or immunological status (Arnau-Bonachera et al, 2017;Penadés et al, 2017). For example, at second parturition, females are still growing and their acquisition capacity is not fully developed, but they are under highly productive conditions.…”

“…In the first paper, we investigated the way three genetic types differing greatly in their genetic background acquire and allocate resources when fed with diets specially designed to influence either the milk production or body reserves (Arnau-Bonachera et al, 2017). In the second paper, we investigated parameters related to the immune system of these genetic types across time and how previous diets affected them (Penadés et al, 2017). In this work, we aimed to evaluate:…”