The sources of genetic structure within breeds and its implications

With companion animals, there is a large diversity in breeding practices, which may impact genetic variability and health of selected breeds. Based on a survey, we illustrate the specificities of scent hound dog breeders regarding either their breeding goals or their mating practices. Mating between close relatives are also investigated in different cat breeds. Such mating are more or less frequent according to breeds and countries, but seems to occur more rarely in the last few years. Deleterious impact of inbreeding on fitness traits is also investigated for four dog breeds. In most cases, litter size and longevity are found significantly reduced for individuals with large inbreeding levels. These results illustrate how some breeding practices, such as mating between close relatives, may have an impact on fitness and welfare in cat and dog breeds. Introduction Selection in companion animals such as dogs or cats differs from other domesticated species as they are generally not raised by production or profits. A large majority of breeders are occasional or hobby breeders and it seems to exist a large diversity of breeding practices according to those breeders (Leroy et al. 2007). Recently, several reports have pointed out the potential deleterious impact that may have some of those selection practices regarding the welfare of purebred dogs (Nicholas 2011), in relation for instance to traits selection which, when taken to extremes, are deleterious to health (Collins et al. 2011). Inbreeding has also been shown to have deleterious impact on traits related to reproduction and occurrences of some diseases (Urfer 2009, Mäki et al. 2001). We propose here to show, on a few examples in dog and cat, the diversity of breeding practices, between breeds, between countries, and over time. Impact of inbreeding depression on litter size and longevity will also be illustrated based on some preliminary results on dog breeds. Breeding practices according to breeds, results from a dog breeders survey In dog species, where breeds shows a particularly large morphological diversity, in relation, among others, to their different uses (pets, hunting, herding...), one may expect to find also a large diversity of breeding goals according to breeds. To investigate if some differences could also be found in relation to selection tools, management methods, and reproduction tools, a survey composed of 55 questions was carried out in 2007 among 985 French dog breeders (Leroy et al. 2007). Two main explanatory variables were used to analyses the results, namely the number of litters produced, and the FCI group of the main breed raised.