ABSTRACT
     This thesis tackles the design of new feeding strategies in the present situation of rabbit production, marked by a high prevalence of Epizootic Rabbit Enteropathy and the systematic use of antibiotics as the usual way to maintain digestive health of growing rabbits and, consequently, the economic viability of the rabbit farms. In this context, the work has been focused in the use of weaning diets in combined feeding of rabbit does and litters.
     In a first experiment, eight weaning diets were formulated according to a factorial design 2×2×2, the factors being: i) the partial replacement of starch with acid detergent fibre, ii) the partial replacement of starch with neutral detergent soluble fibre and iii) the reduction of crude protein content. The experimental diets were administrated to the rabbit does and their litters from 17th day of lactation to weaning at 28 days; after weaning, young rabbits continued receiving the experimental diets until 49 days when they were switched to a commercial growing diet until 60 days. In general, the dietary changes under study affected negatively milk yield and body condition of rabbit does at weaning, as well as litter weight at weaning. However, these changes reduced the mortality rate in young rabbits after weaning, showing additive effects.
     In a second experiment, the effect of the eight previous diets on caecal environment of growing rabbits was studied. Samples were obtained from animals slaughtered at 35 days of age, which were receiving one of the eight experimental diets from 17th day and were weaned at 28 days. The dietary changes mainly affected the caecal concentration of volatile fatty acids (by increasing) or/and of ammonia (by decreasing), establishing a more favorable environment to maintain the stability of the caecal microbial ecosystem and, consequently, the digestive health which would explain the reduction in mortality rate observed in the previous experiment.  
     In the third experiment, the long term effects of a feeding system based in the use of a less concentrated weaning diet (shown as beneficial to digestive health of growing rabbits according to the results obtained in the previous experiments) and of an extensive reproductive system (insemination at 25 days and weaning at 42 days) were studied with a factorial design 2×2, by comparing with the conventional feeding system and the semi-intensive reproduction system (insemination at 11 days and weaning at 28 days) during five productive cycles. As in the first experiment, the weaning diet was administrated from 17th day of lactation to weaning in the case of rabbit does and to 49 days in the case of young rabbits. The feeding system based in the use of a less concentrated weaning diet and the extensive reproductive system led to several negative effects through the successive cycles (lower milk yield, lower live weight of rabbit does, lower litter weight at birth, lower weight of young rabbits at weaning), revealing an adaptation process of rabbit does to both limited availability of resources and higher physiological effort because of longer lactations. On the contrary, both strategies decreased mortality rate of growing rabbits. 
     To summarize, the results of this thesis show that both the use of less concentrated weaning diets and the delay of the weaning age impaired the performance of rabbit does and reduced the mortality rate of growing rabbits in a context of Epizootic Rabbit Enteropathy. Nevertheless, even considering this reduction, the registered mortality rates were clearly higher to the acceptable ones in a rational and viable rabbit production system.