Genetic improvement of meat rabbits. Programmes and diffusion.

The essential elements of a programme of genetic improvement of meat rabbits, required to satisfy the needs of animals demanded by the producers of rabbit meat in a region or country, are analysed. The three way crossbreeding scheme is adopted to discuss the programmes. In this context, the development of maternal and paternal lines is one of the central points and a historical enumeration of research or development centres involved in this activity is presented. The principal criteria in founding new lines are discussed and the interest is noted in finding two or three populations, no matter their genetic origin (pure breed, synthetics or crossbred), that are clearly outstanding for the traits important to the desired specialisation of the line. The alternative of applying very high intensities of selection for the traits of interest in very large populations is also commented upon (for example, commercial populations made up by a large number of farms) and examples of founding a line following criteria of hyperprolificacy and another of hyperlongevity are given. Paternal lines are commonly selected for post-weaning daily gain or weight at time of marketing by individual selection. The most common criterion used to select maternal lines is litter size at birth or at weaning, but there are proposals to include traits related with the ability of the doe to nourish the lactating progeny, traits such as weight at weaning, litter weight at weaning or total milk production. Currently, mixed model methodology (BLUP) is the habitual procedure used to evaluate the animals genetically, using repeatability animal models for litter size and selecting the progeny from the best evaluated matings. The responses reported in paternal lines range between 18 and 35 g/generation for weight at market time and between 0.45-1.23 g/d. generation for daily gain, with correlated responses increasing adult weight, intestinal content and feed intake but decreasing feed conversion, dressing percentage and maturity at a fixed weight. The responses estimated in maternal lines range between 0.05-0.13 rabbits born alive or weaned per litter and generation, figures 0.080.09 being common. Depending on the lines, ovulation rate or foetal survival were the modified components that explain the responses in litter size. Comparing the responses in crossbreeds with the responses in pure lines, slightly higher responses were obtained for the crossbred does; however, the response was lower than expected for the young issued from the terminal mating, probably due to an interaction between the feed currently used to control enterocolitis and the genetic level for growth traits. Finally, two approaches to diffuse the genetic improvement to the producer are presented which modify the standard pyramid of selection, multiplication and production, aiming to increase the selection effort and minimise the genetic lag between selection and