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

GROUP BREEDING SCHEME:
A FEASIBLE SELECTION PROGRAM
Yves M. Berger
Spooner Agricultural Research Station
University of Wisconsin-Madison
Spooner, Wisconsin
Introduction
Every flock owner practices some sort of selection on his/her flock by keeping ewe lambs or
ram lambs from their best ewes for the trait(s) they have chosen. In traditional sheep flocks the
selection criteria most often chosen by producers are prolificacy, growth, out of season lambing,
easy care sheep, etc… In a dairy sheep flock, selection is done on milk production, milk composition,
udder morphology, milk let down, etc… In other words we all want the perfect sheep that
is high producing with the least amount of work at the least cost. Real genetic progress in individual
small to medium size flocks is, generally, not forthcoming because of ill chosen traits to
improve (or too many), small number of animals to choose from and inaccuracy of the estimated
genetic value of the animal selected. A quick reminder of genetic principles might help understand
the reasons for the poor or no results from an individual flock selection program.
Genetic review
Two terms are absolutely indispensable to understand:
Heritability. Heritability (h 2 ) is the proportion of phenotypic differences between animals
which is due to additive genetic differences. Simply put, it is the proportion of parent superiority
observed in the progeny. In general reproductive traits have a low heritability while growth,
carcass traits, fiber traits and milk production have a medium heritability. The following table
gives a few examples of heritabilites in sheep:
Prolificacy 10%
Lamb survival 5%
90-day weight 25%
Loin eye area 50%
Fiber diameter 40%
Milk yield 30%
Milk Fat percentage 35%
Milk Protein percentage 40%
The higher the heritability, the quicker the selection will be. In sheep, dairy traits have a
moderate heritability, which means that significant genetic improvement can be achieved.