Assessment of mating management effect on genealogical parameters highlighting the genetic variability in a not closed fat-tailed Barbarine sheep pedigree

Abstract. The Barbarine sheep is generally managed within small interconnected herds. The goal of the present work is to investigate the effect of the mating management on genetic variability in a registered flock which starts showing a productivity falling, especially in lamb’s survival and this despite a practice of outbreeding. Pedigree data of 11136 animals born between 1977 and 2007 were used to compute genealogical parameters. A first investigation of the lambs-parents relationships highlighted two periods that we denoted: P1 and P2. During P1, the mating strategy had been progressively based on animals born within the flock, whereas during P2, ewes and rams coming from outside the herd were gradually introduced as parents with unknown genealogy. This change in matings policy has been emphasised by plotting equivalent complete generations averaged whether by year of birth or maximum number of traced generations. All the computed genealogical parameters have been affected by the matings policy change and especially the individual average relatedness and realised effective size, which seem to be powerful tools to monitor the genetic variability within a population that is not closed to exchanges. An important effect of pedigree depth has been detected; this would require special attention to the matings of individuals with deepest genealogy. In spite of this effect, the heterozygote deficiency within the herd confirmed that the genetic variability has not been much affected along the flock life, which confirms that the decline in productivity should not be allotted to matings’ policy, but probably to other management factors.