Segregation of a major gene influencing ovulation in progeny of Lacaune meat sheep

Abstract

-Inheritance of the ovulation rate (OR) in the Lacaune meat breed was studied through records from a small nucleus of 36 hyper-prolific ewes screened on farms on the basis of their natural litter size, and from progeny data of three selected Lacaune sires. These sires were chosen at the AI centre according to their breeding values estimated for the mean and the variability of their daughters' litter size. Non-carrier Lacaune dairy ewes were inseminated to produce 121 F1 daughters and 27 F1 sons. Twelve sons (four from each sire) were used in turn to inseminate non-carrier Lacaune dairy ewes providing 260 BC progeny ewes. F1 and BC progeny were brought from private farms and gathered after weaning on an experimental farm where ovulation rates were recorded in the first and second breeding seasons. With an average of 6.5 records each, the mean OR of hyper-prolific ewes was very high (5.34), and 38.4% of records showed a rate of 6 or more. F1 data showed high repeatability of OR (r = 0.54) within ewe, with significant variability among ewes. High OR (≥ 4) were observed in each * Correspondence and reprints E-mail: bodin@toulouse.inra.fr 448 L. Bodin et al.family. A segregation analysis provided a significant likelihood ratio and classified the three founders as heterozygous. BC ewes also displayed high repeatability of OR (r = 0.47) and the mean OR varied considerably between families (from 1.24 to 1.78). Seven of the 12 BC families presented high-ovulating ewes (at least one record ≥ 4) and segregation analysis yielded a highly significant likelihood ratio as compared to an empirical test distribution. The high variability of the mean ovulation rate shown by a small group of daughters of BC ewes inseminated by putative carrier F1 rams, and the very high ovulation rate observed for some of these ewe lambs, confirmed the segregation of a major gene with two co-dominant alleles borne by an autosome. The difference between homozygous non-carriers and heterozygous ewes was about one ovulation on the observed scale and 2.2 standard deviations on the underlying scale.sheep / major gene / ovulation

Major genes affecting ovulation rate in sheep

“…Progeny testing and a subsequent segregation analysis supported the earlier data and indicated the presence of an autosomal gene with one copy increasing the ovulation rate by 1.03 [24]. Further analysis of records from the subset of ewes and progeny test data from three rams and 12 of their sons in a backcross experiment enabled putative heterozygous and homozygous ewes to be compared and this indicated that the effect of the gene is additive for ovulation rate in a manner similar to that of the Booroola gene [4]. A genome scan localised the Lacaune gene to chromosome 11 and identified 10 markers around the Lacaune locus [24].…”

“…The presence of some ewes with extremely high ovulation rates led Bodin et al [4] to speculate that several alleles may be present or possibly other major genes within the screened group of ewes. Recently a mutation of BMP15, different from FecX I , FecX H , FecX G and FecX B , has been discovered in the Lacaune breed and work is in progress to determine the phenotype of ewes carrying this mutation (Bodin, personal communication).…”

“…The high variation in ovulation rate (range [1][2][3][4][5][6][7][8] and litter size (range 1-7) combined with high repeatabilities are characteristic of flocks where a major gene is segregating. The repeatability of ovulation rate was 0.8 which is similar to that recorded in Javanese (0.6, [5]), Booroola (0.6-0.7, [7]), Cambridge (0.7, [17]), and Icelandic (0.6-0.8, [14]) sheep, which are all breeds with segregating major genes for prolificacy.…”

Fine mapping of the FecL locus influencing prolificacy in Lacaune sheep

“…1992), Woodlands ( FecX2 , Davis et al. 2001), Lacaune ( FecL , Bodin et al. 2002) and Wishart ( FecW , Davis et al.…”

“…Several strains exist, each being bred for a specific purpose – either milk for the dairy strain or suckling lamb for the meat strain. In the Lacaune meat breed population, inheritance of OR was hypothesized to be under the control of an autosomal gene of major additive effect named FecL (Bodin et al. 2002).…”