An effective rotational mating scheme for inbreeding reduction in captive populations illustrated by the rare sheep breed

Within breeds and other captive populations, the risk of high inbreeding rates and loss of diversity can be high within (small) herds or subpopulations. When exchange of animals between different subpopulations is organised according to a rotational mating scheme, inbreeding rates can be restricted. Two such schemes, a breeding circle and a maximum avoidance of inbreeding scheme, are compared. In a breeding circle, flocks are organised in a circle where each flock serves as a donor flock for another flock, and the same donor–recipient combination is used in each breeding season. In the maximum inbreeding avoidance scheme, donor¿recipient combinations change each year so that the use of the same combination is postponed as long as possible. Data from the Kempisch Heideschaap were used with computer simulations to determine the long-term effects of different breeding schemes. Without exchanging rams between flocks, high inbreeding rates (>1.5% per year) occurred. Both rotational mating schemes reduced inbreeding rates to on average 0.16% per year and variation across flocks in inbreeding rates, caused by differences in flock size, almost disappeared. Inbreeding rates with maximum inbreeding avoidance were more variable than with a breeding circle. Moreover, a breeding circle is easier to implement and operate. Breeding circles are thus efficient and flexible and can also be efficient for other captive populations, such as zoo populations of endangered wild specie

Toekomst voor zeldzame Nederlandse Landbouwhuisdierrassen : Stimulans voor het behoud van levend erfgoed

Adviesrapport van de Stichting Zeldzame Huisdierrassen (SZH) en het Centrum voor Genetische Bronnen, Nederland van Wageningen UR (CGN) aan LNV over reële en kansrijke mogelijkheden voor nieuwe vormen van ondersteuning van in situ conservering van zeldzame rassen landbouwhuisdieren in Nederland, die op voldoende draagvlak kunnen rekenen. De behoefte aan dit advies hangt samen met de verdere uitwerking van de in het Nederlandse landenrapport over dierlijke genetische bronnen genoemde beleidsprioriteiten (LNV, 2002). In het landenrapport staat onder andere dat Nederland zich ten doel stelt om Nederlandse zeldzame rassen landbouwhuisdieren het predikaat zeldzaam te laten ontgroeien zonder structurele subsidiëring van de overhei

Varkansen : springplank naar een duurzame veehouderij : varkenshouderij met neus voor dier, ondernemer, milieu en burger-consument

'Varkansen' laat ontwerpen van integraal duurzame varkenshouderij zien. Aanleiding is de 'Toekomstvisie op de duurzame veehouderij'. Daarin staat dat de veehouderij over 15 jaar duurzaam moet zijn, dus produceert met respect voor mens, dier en milieu

Survey of organisation, actual stocks, and procedures of Ex situ conservation of Heritage Sheep Breed

This report describes the results of a survey of the organisation and procedures of ex situ conservation of Heritage Sheep breeds in France, Greece, the Netherlands, and the United Kingdo

Breeding programmes for elimination of alleles in rare breeds: scrapie in the Netherlands

Small populations often suffer from genetic defects. Single gene defects can be eliminated by selection for specific alleles, but then there is a risk of increased inbreeding with associated loss of genetic variation, inbreeding depression and increased frequency of other genetic defects. Here we investigate special breeding programs for scrapie resistance with inbreeding restriction. A ram circle, where each flock uses rams from another flock, is most suited for situations where pedigrees are unknown and animals are herded in large flocks. Inbreeding minimization with optimal contribution theory is most suited when pedigree records are available and a few breeders provide most rams for the whole population. Both schemes considerably reduced inbreeding rates in the Kempisch Heideschaap and in the Mergellande

Selection for scrapie resistance and simultaneous restriction of inbreeding in the rare sheep breed "Mergellander"

Scrapie is a fatal infectious neurodegenerative disease for which susceptibility is associated with polymorphisms in the ovine prion protein (PrP) gene. Scrapie-eradication programmes are based on eliminating the susceptible VRQ allele and/or breeding for the resistant ARR allele. In rare breeds or breeds with a low frequency of the ARR allele this can lead to unacceptably high inbreeding rates with associated increased risk of genetic defects and inbreeding depression. The conservation status of populations with inbreeding rates (¿F) above 1% is considered critical. In the Dutch rare sheep breed the Mergellander animals carrying ARR alleles are closely related to one another, and could reach 1.53% when only ARR/ARR animals are used as parents. Inbreeding rates can be reduced by selecting the set of parents according to their average co-ancestry. We minimised inbreeding rates by calculating the optimal contribution of each ram and selection of ewes. This resulted in inbreeding rates of ¿0.17% with exclusive use of homozygous ARR rams, and ¿0.38% if use of heterozygous rams was allowed as well. Thus sophisticated breeding programs can prevent unacceptably high inbreeding rates when breeding for scrapie resistance

Effects on inbreeding of different strategies aimed at eliminating scrapie sensitivity alleles in rare sheep breeds in the Netherlands

The Dutch scrapie eradication programme aims at the exclusive use of homozygous ARR/ARR breeding rams by the end of 2004. As a consequence, breeds with a small population size and a low frequency of the ARR allele may suffer unacceptable losses of genetic diversity and high inbreeding levels. We simulated three breeding strategies to assess their efficacy in eliminating scrapie sensitive alleles and their effect on inbreeding levels. Under mild selection, both homozygous and heterozygous ARR rams were used indiscriminately. Under moderate selection, homozygous ARR rams were used preferably but they were supplemented with heterozygous rams when necessary. Under severe selection, only homozygous rams were used. Severe selection mimics then the proposed eradication programme. Simulations were carried out with allelic frequencies and population parameters of existent rare breeds in The Netherlands. With severe selection all simulated breeds showed unacceptably high inbreeding rates (>0.5% per year). For some breeds, moderate selection resulted in acceptable inbreeding rates, while for other breeds only mild selection resulted in acceptable rates. The frequency of the ARR allele after 5 years of selection was only slightly lower with moderate selection than with severe selection (0.8% lower on average), but it was clearly lower with mild selection. Based on these simulations, we propose a selection programme where with low frequencies of the ARR allele, mild selection is used initially. Once the ARR frequencies rise to a particular value, the switch can be made to moderate selection. The population size (e.g. below 750, 750 to 3750 and above 3750 ewes) determines the frequency of the ARR allele at which the switch can be made (33%, 25% and 10%, respectively). With even higher ARR frequencies (above 70%, 50% and 33%, respectively) the regime can be changed to severe selectionThe Dutch scrapie eradication programme aims at the exclusive use of homozygous ARR/ARR breeding rams by the end of 2004. As a consequence, breeds with a small population size and a low frequency of the ARR allele may suffer unacceptable losses of genetic diversity and high inbreeding levels. We simulated three breeding strategies to assess their efficacy in eliminating scrapie sensitive alleles and their effect on inbreeding levels. Under mild selection, both homozygous and heterozygous ARR rams were used indiscriminately. Under moderate selection, homozygous ARR rams were used preferably but they were supplemented with heterozygous rams when necessary. Under severe selection, only homozygous rams were used. Severe selection mimics then the proposed eradication programme. Simulations were carried out with allelic frequencies and population parameters of existent rare breeds in The Netherlands. With severe selection all simulated breeds showed unacceptably high inbreeding rates (> 0.5% per year). For some breeds, moderate selection resulted in acceptable inbreeding rates, while for other breeds only mild selection resulted in acceptable rates. The frequency of the ARR allele after 5 years of selection was only slightly lower with moderate selection than with severe selection (0.8% lower on average), but it was clearly lower with mild selection. Based on these simulations, we propose a selection programme where with low frequencies of the ARR allele, mild selection is used initially. Once the ARR frequencies rise to a particular value, the switch can be made to moderate selection. The population size ( e. g. below 750, 750 to 3750 and above 3750 ewes) determines the frequency of the ARR allele at which the switch can be made (33%, 25% and 10%, respectively). With even higher ARR frequencies (above 70%, 50% and 33%, respectively) the regime can be changed to severe selection