Dairy Sheep Symposium - the Department of Animal Sciences ...

NEW DEVELOPMENTS IN THE GENETIC IMPROVEMENT OF DAIRY SHEEP
J.J. Arranz 1 , Y. Bayón 1 , D. Gabiña 2 , L.F. de la Fuente 1 , E. Ugarte 3 and F. San Primitivo 1
1 Dpto. Producción Animal, Universidad de León, 24071 León, Spain
2 IAMZ-CIHEAM, Apartado 202, 50080 Zaragoza, Spain
3 NEIKER, Granja Modelo de Arkaute, Apdo 46, 01080 Vitoria-Gasteiz, Spain
Introduction
Sheep have been traditionally farmed to take advantage of nutritional resources non-usable by
other species, in geographic areas with hard environmental conditions, or as a complement of
economically more interesting species. Management systems in sheep generally involve an important
extensive component that is specific for each region and breed, but dairy sheep must also adapt to
milk management procedures and this constitute a serious limiting factor for certain indigenous
sheep. In the Mediterranean area ovine milk production is mainly manufactured as gourmet or
artisanal farmhouse cheese, economically of high importance in these countries.
In comparison with dairy cattle, selection schemes have been applied much later in sheep. The
application of these quantitative genetic methods has produced a remarkable increase in milk yield
and farmer livelihood in the different sheep breeds (Haenlein, 2001). However, the genomic
revolution occurred in the recent years will hopefully provide, in the near future, valuable
complements to classical breeding methods.
The possibility of access to the molecular architecture of production traits will presumably
permit a more efficient selection. Expectedly, the identification of particular chromosomal
segments explaining part of the additive variance (QTL), will make the identification of the
genes underlying these traits possible. But in the meanwhile, it is necessary to better manage the
productive factors known to influence the profitability of sheep enterprises.
The ovine milk is mainly orientated towards the fabrication of cheese, and consequently
parameters affecting “cheese yield” should be “selection objectives”. The difficulty to directly
measure this trait makes selection possible only on the basis of indirect traits as milk protein and
milk fat contents. The establishment of a trustworthy method for the measurement of the cheese
yield would improve dairy sheep selection.
Another important aspect is sheep husbandry. An animal affected by a pathological process
cannot express all its genetic potential, and this not only causes a direct decrease in production
but also influences negatively the future generations since a correct genetic evaluation of the
reproducers is not possible.
Improvement of reproductive technology is also of importance in sheep breeding since it
largely affects both the flock production and the progress of the genetic improvement. The low
fertility obtained at the moment with the AI, the difficulties in semen conservation and other
limiting factors, negatively influence the efficiency of selection programs applied in sheep.
In this paper we will try to briefly approach all these aspects, with particular attention to
those in which we have more research experience.
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