Dna Markers for Aseasonality and Milk Production in Sheep

Knowledge about genetic markers linked to genes affecting quantitative traits can increase the selection response of animal breeding programs, especially for traits that are difficult to improve when using traditional selection (Meuwissen and Goddard, 1996; Meuwissen and Van Arendonk, 1992). The seasonal breeding pattern that is commonly observed in temperate sheep breeds is a major obstacle to increasing the intensity of sheep production. Sheep breeds differ in timing and duration of breeding (Notter D.R., 1992; Nugent et al., 1988; Vincent et al., 2000) but less is known about genetic variation within breeds for traits associated with seasonal breeding. There-fore, selection of sheep for aseasonal reproduction is based upon observing the animals’ pheno-type, which often lacks accuracy and can be done only after animals reach sexual maturity. Similarly, selection for milk production is difficult for at least two reasons. First, measuring the trait takes time and money (females need to reach maturity before expressing the trait and the lactation period lasts more than 200 days so repeated measurements are necessary to accurately assess the phenotype). Second, milk yield is a sex limited trait; therefore the males, the most important path for selection because of their higher reproductive capacity, can be evaluated only based on the phenotype of their female progeny. Furthermore, for both traits the exact molecular nature of the target genes remains essentially unknown.