On account of the mean marketing age of lambs in FRANCE, selection on growth is made in the farms on an early criterion, i.e. weight at 70 days or daily mean gain between 30 and 70 days (PERRET and BIBE, 1979). Such a criterion gives rise to the problem of the influence of the maternal effect which remains large at that age for lambs suckled by their dams. Furthermore, this growing period does not allow any discrimination between animals with a high maturity rate (early maturing animals) or a low maturity rate (late maturing animals), while the latter are the most interesting ones genetically for intensive production of heavy lambs without any excess of fat.
On the other hand, within the collective selection schemes involving rearing centres for young males intended for controlling the management of male breeding animals proceeding from planned matings, it is possible to define more efficient selection criteria than the previous ones on growth and carcass value. Such an option requires a more accurate determination of management conditions such as age at which the animals enter the rearing centre, length of stay and feeding liable to affect the genetic growth parameters.
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 8. Symposia (2), , 712-718, 1982
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