Free Access
Genet. Sel. Evol.
Volume 34, Number 4, July-August 2002
Page(s) 447 - 464

Genet. Sel. Evol. 34 (2002) 447-464
DOI: 10.1051/gse:2002017

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

Loys Bodina, Magali SanCristobalb, Frédéric Lecerfb, Philippe Mulsantb, Bernard Bibéc, Daniel Lajousa, Jean-Pierre Bellocd, Francis Eychennee, Yves Amiguesf and Jean-Michel Elsena

a  Station d'amélioration génétique des animaux, Institut national de la recherche agronomique, BP 27, 31326 Castanet-Tolosan, France
b  Laboratoire de génétique cellulaire, Institut national de la recherche agronomique, BP 27, 31326 Castanet-Tolosan, France
c  Département de génétique animale, Institut national de la recherche agronomique, BP 27, 31326 Castanet-Tolosan, France
d  Coopérative OVI-TEST, Route d'Espalion, 12850 Onet-le-Château, France
e  Domaine expérimental de Langlade, 31450 Montgiscard, France
f  Labogena, Domaine de Vilvert, 78352 Jouy-en-Josas, France

(Received 17 September 2001; accepted 13 February 2002)

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 ( $\geq 4$) were observed in each 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 $\geq 4$) 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.

Key words: sheep / major gene / ovulation

Correspondence and reprints: Loys Bodin

© INRA, EDP Sciences 2002