252. Morphometric and histological analysis of ovaries from sheep heterozygous for the prolific woodlands allele
E. S. Feary A C , J. L. Juengel A , P. Smith A , A. R. O’Connell B , G. H. Davis B and K. P. McNatty AA Reproductive Biology, Wallaceville, Animal Research, Upper Hutt, New Zealand
B Agricultural Centre, AgResearch, Invermay, Dunedin, New Zealand
C Victoria University, Wellington, New Zealand
Reproduction, Fertility and Development 17(9) 101-101 https://doi.org/10.1071/SRB05Abs252
Submitted: 26 July 2005 Accepted: 26 July 2005 Published: 5 September 2005
Abstract
Woodlands are a line of Coopworth sheep with a novel, imprinted X-linked fecundity allele resulting in ovulation rates about 0.40 higher than wild-type animals. Daughters of progeny tested sires with and without the gene were studied.
Previously, lambs heterozygous for the Woodlands allele were found to have larger ovaries and more antral (i.e. type 5) but not preantral (i.e. types 1–4) follicles than in wild-type contemporaries. The large ovary phenotype was found to be transient and was absent after puberty. However, based on follow-up studies it was evident that the large ovary phenotype was not strongly associated with the Woodlands fecundity allele. Thus, it was uncertain whether animals carrying the Woodlands gene had different follicular populations compared to wild-type controls. To address this question, follicular populations were compared in adult ewes heterozygous for the Woodlands allele with age-matched controls. Using standard morphometric methods and histological analysis, no differences were observed in the mean numbers of types 1, 1a, 2, 3 and 4 preantral follicles between the genotypes. Furthermore, no differences were observed between genotypes in follicular or oocyte diameters for any follicular type. The adult Woodlands carrier ewes had twice as many small type 5 follicles (< 1mm) when compared to wild-type contemporaries although no difference was seen in the numbers of antral follicles > 1mm in diameter. In addition, antrum formation occurred at a smaller follicular diameter in the heterozygous Woodlands animals.
Therefore, the increased number of antral follicles observed in both lambs and adult ewes suggests that this difference in pattern of follicular development is associated with the X-linked fecundity allele. This novel phenotype of early antrum formation and larger number of small preantral follicles differs from that observed in sheep with the Inverdale or Booroola mutations, suggesting that a different mechanistic pathway is involved.
Acknowledgements: The Marsden Fund, FRST and Ovita.
