Populatieonderzoek bij het Mergellandschaap: trends en toekomst: Een genetische analyse van populatiedynamiek, inteelttoename en duurzame behoudsstrategieën

The Mergelland sheep is one of the rare native Dutch livestock breeds. Monitoring trends in the number of breeding animals and the rate of inbreeding is essential for the conservation of rare breeds. In 2024, the Center for Genetic Resources, the Netherlands (CGN) conducted a population genetic analysis for the Mergelland sheep. The number of registered lambs born per year is decreasing and the share of the most used rams is disproportionately large. The number of lambs a ewe produces in her lifetime has been declining since 1993. This could be a sign of reduced fertility due to inbreeding depression. The rate of inbreeding in the last 4 to 5 generations is 0.73% per generation and is therefore higher than desired. Various measures were compared using computer simulations to determine how a reduction in the expected rate of inbreeding could best be achieved. The herdbook already uses a breeding restriction, which limits the number of sons per ram that can be used in breeding. The simulations showed that this limitation indeed has a small beneficial effect on reducing the inbreeding rate. A combination of a breeding restriction in the form of a maximum number of ewes that the ram may cover in his life, and selecting animals with a low mean kinship led to a greater reduction in the inbreeding rate. Following this research into the Dutch population of Mergelland sheep, CGN recommends to consider the combination of these measures, and to stimulate members to register all lambs.