J. Anim Sci.
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J. Anim. Sci. 2003. 81:912-917
© 2003 American Society of Animal Science

Evaluation of melatonin receptor 1a as a candidate gene influencing reproduction in an autumn-lambing sheep flock

D. R. Notter*,1, N. E. Cockett{dagger} and T. S. Hadfield{dagger}

* Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg 24061 and and {dagger} Department of Animal, Dairy, and Veterinary Sciences, Utah State University, Logan 84322

1 Correspondence:
phone: 540-231-5135; fax: 540-231-3010; E-mail:
drnotter{at}vt.edu.

The effect of the melatonin receptor 1a (MTNR1A) gene on fertility and litter size in autumn lambing was studied with 373 ewes from a population of sheep selected for 10 yr for fertility in May and June matings. Animals were from a composite line of 50% Dorset, 25% Rambouillet, and 25% Finnsheep. Two restriction fragment length polymorphisms were present in the population, with allelic frequencies of 0.42 and 0.58 for an MnlI polymorphism (alleles M and m, respectively) and of 0.34 and 0.66 for an RsaI polymorphism (alleles R and r, respectively). Genotypic frequencies for the polymorphisms were not independent, suggesting an association between them in foundation animals. Effects of MTNR1A genotype on fertility and litter size were evaluated using mixed linear model or REML procedures, but were not significant for matings involving ewes of all ages. However, in adult ewes (3 yr old and older), fertility of ewes of genotype mm was 10.0 (mixed model; P < 0.09) to 11.2% (REML; P = 0.03) less than that of other ewes. Genotypic effects associated with MTNR1A in adult ewes accounted for 23.8% of the estimated total additive genetic variance in fertility. Litter size was not significantly associated with MTNR1A genotype; adult ewes of genotype mm had approximately 0.11 fewer lambs per ewe lambing than ewes of other genotypes. Fertility in autumn lambing is lowly heritable, expressed only in females, and manifested relatively late in life and only in some management systems. Access to genetic markers would thus be advantageous in selection programs.

Key Words: Genetic Markers • Melatonin • Receptors • Reproduction • Selection • Sheep






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