Genet. Sel. Evol. 37 (2005) S39-S53
DOI: 10.1051/gse:2004031

Opportunities for detection and use of QTL influencing seasonal reproduction in sheep: a review

David R. Notter^a and Noelle E. Cockett<sup>b

a</sup>  Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA
^b  Department of Animal, Dairy and Veterinary Sciences, Utah State University, Logan, Utah, USA

(Accepted: 16 August 2004)

Abstract -
Genetic improvement in traits associated with seasonal breeding in sheep is challenging because these traits have low heritabilities, are generally not expressed until late in life, are commonly recorded only in females, and are expressed only in some lambing seasons and management systems. Detection of quantitative trait loci and their use in marker-assisted selection could therefore substantially enhance selection responses. A population of sheep with an extended breeding season was developed through selection for fertility in spring matings and provides opportunities for further study of candidate genes influencing seasonal breeding. In particular, the melatonin receptor 1a gene is polymorphic in many sheep breeds and appears to influence a number of seasonal reproductive responses. In addition, a variety of clock genes have been identified in laboratory mammals and shown to influence biological rhythms. Mutations in these clock genes have been identified and shown to influence circadian periodicities and reproductive patterns in golden hamster and mouse. In sheep, expression of clock genes in the suprachaismatic nucleus and pars tuberalis (PT) suggests that "calendar" cells in the ovine PT play a role in maintaining circannual rhythms. Thus the various clock genes represent potentially important candidate genes that may be involved in control of  seasonal breeding.

Key words: sheep / seasonal breeding / selection / melatonin receptor la / clock genes

Correspondence and reprints: drnotter@vt.edu

© INRA, EDP Sciences 2004