Resumen de OPTIMIZATION OF RESOURCE ALLOCATION TO THE GENETIC TYPE IN REPRODUCTIVE RABBIT DOES
During the last 50 years, there has been an overall improvement of efficiency in all domestic species thanks to an improvement in productivity traits. However, during the last years, disorders associated to a loss of functionality of animals (such as poor fertility, health and longevity of reproductive females) with high productivity standards have been observed. In this scenario, interactions between genetics and nutrition are becoming relevant. The main hypothesis of the present thesis is that nutritional strategies adapted to the genetic type could help to modulate productivity and functionality of females in the long term. To evaluate this hypothesis, 203 rabbit females were used which gave birth a total of 758 litters. These females belonged to 3 genetic types that differed greatly on their breeding goals: H, maternal line characterised by hyper-prolificacy; LP, maternal line characterised by functional hyper-longevity; R, paternal line characterised by growth rate. Females were fed during 5 consecutive reproductive cycles with 2 iso-energetic and iso-protein diets differing in energy source: Animal fat enhancing milk yield (84 g of ether extract per kg of DM and 105 g of starch per kg of DM); Cereal starch promoting body reserves recovery (21 g of ether extract per kg of DM and 237 g of starch per kg of DM). This experiment generated a set of longitudinal data with particular structures of (co)variances among data which had to be taken into account. Several models differing in the way data structure is modelled were evaluated. We found that none of the tested models was the best in terms of goodness of fit to the data for all traits, but it seems that models in which (co)variance structure was modelled in blocks of (co)variances for each reproductive cycle could be the most recommendable because they presented an overall suitable statistic performance (in terms of parsimony and fitting) and biological interpretation. These models provided useful information to understand acquisition and allocation of individual animals. In this sense, it seems that we can modulate allocation between energy addressed to milk or to body reserves by changing energy source of diet, but altering normal homeostasis of animals. Respect to the strategies of genetic types, results of the present experiment seem to indicate that R females were characterized by greater adult weight and by a high dependence on the body reserves to cope with the reproductive requirements of the current reproductive cycle. They gave birth little but heavier kits, although it seems they could be more immature. When R females were fed with a diet promoting milk yield, they invested more on the current litter, whereas when fed with a diet promoting body reserves recovery, it seems that they invested more in recovering for future reproduction. On the contrary, females from the maternal lines were smaller and had numerous but lighter kits, but each genetic type used different strategies. H females were also high dependent on body reserves, but storing body reserves during lactation to cope with future reproduction. This strategy makes them more sensible to the energy source of the diet, triggering problems to ensure future reproduction when fed with a diet promoting body reserves recovery (low conception rate or higher mortality of females). LP females were characterised by an acquisition capacity better fitted to changing requirements, safeguarding body reserves. This strategy seems to be more generalist, allowing them to ensure high performance of the current litter without neglecting future reproduction and with less sensitivity to the diet. Therefore, to properly balance between productivity and functionality, results reported in the presented thesis suggest that apart from requirements, the way each genetic type acquire and allocate energy over its life trajectory should be considered when formulating diets for reproductive rabbit females.
