Abstract
The development of inbreeding in rotation breeding schemes, sequentially using artificial insemination (AI) sires over generations, was investigated for a full AI scheme. Asymptotic prediction formulae of inbreeding coefficients were established when the first rotation list of AI sires (possibly related) was in use. Simulated annealing provided the optimal rotation order of sires within this list, when the sires were related. These methods were also used for subsequent rotation lists, needed by the exhaustion of semen stores for the first bulls. Simulation was carried out starting with groups of independent sires, with different sizes. To generate a yearly inbreeding rate substantially lower than 0.05% (considered to be within reach by conventional conservation schemes using frequent replacements), the results obtained showed that the number of sires should be at least 10–15 and that the same sires should be used during at least 50 years. The ultimate objective was to examine the relevance of implementing rotation in breeding schemes on the actual rare French cattle breeds under conservation. The best candidate for such a test was the Villard-de-Lans breed (27 bulls and 73 000 doses for only 340 females) and it turned out to be the best performer with an inbreeding coefficient of only 7.4% after 500 years and five different sire lists. Due to the strong requirements on semen stores and on the stability of population size, actual implementation of this kind of conservation scheme was recommended only in special ('niche') cattle populations.
Highlights
Conservation of endangered cattle breeds often involves only several tens or hundreds of individuals
The lifetime of dams can be more or less considered as imposed by the biology of the species. This behaviour still influences breeders of endangered cattle breeds, who are reluctant to use the same sires during very long periods, semen collection is easy in this species and could provide the stores needed
When a single non-inbred sire is used throughout over generations, the female gene pool tends towards the gene pool of this sire and the inbreeding coefficient tends towards the probability of sampling the same allele in the sire gene pool twice i.e., 0.5
Summary
Conservation of endangered cattle breeds often involves only several tens or hundreds of individuals. Breeders face (and even underestimate) this risk because they are primarily interested in genetic gains and replace breeding animals frequently, especially sires. The lifetime of dams can be more or less considered as imposed by the biology of the species This behaviour still influences breeders of endangered cattle breeds, who are reluctant to use the same sires during very long periods, semen collection is easy in this species and could provide the stores needed. Very long-term (500 years) deterministic and Monte-Carlo simulations of the rotational AI scheme will be implemented to model some real populations This time span for evaluating the potential of breeding schemes to contain the development of inbreeding might look excessive and it might be argued that this view is immaterial, given the numerous extraneous risks incurred by rare populations. That good genetic management is not enough to prevent a rare population from disappearing and that strong economic incentives should be found by the corresponding breeders and (or) provided to them
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