In recent years genetic improvement programmes for sheep in the UK have been primarily directed towards the improvement of growth and carcase traits. The possible correlated responses in other production traits, that may not be of such obvious economic importance, have not been fully assessed. Birth weight is such a trait.

Although of no direct economic importance, birth weight is an important trait in sheep production. There is a known relationship between birth weight and lamb survival, with lambs of both low and very high birth weight being at greater risk. There have, however, been very few genetic studies of the trait. The aim of this study, which is part of a larger project covering a number of breeds, was to estimate the direct and maternal heritability of birth weight and its genetic correlations with 8 week weight in the Dorset Down and Hampshire Down breeds. In addition the genetic trend in birth weight over a fourteen year period is assessed.