The significance of interactions in practical sheep breeding in northern Europe

A brief summary of the sheep breed population in Eire, Scandinavia and United Kingdom is presented.The large number of breeds in the U.K. suggests that genotype environment interactions may well exist. Experimental evidence of both between breed and, more importantly, of within breed G × E interaction is summarised together with circumstantial evidence from the industry.The implications of such evidence are discussed in relation to the national improvement programme for each type of breed — hill, longwool and down breeds. The conclusion is that for hill breeds selected for reproduction traits the possibility of G × E interactions cannot be ignored, whereas for the slaughter sire breeds there appears to be less likelihood of serious effects. Some evidence suggests that artificial rearing, although an unnatural environment, can improve the rate of progress rather than decrease it.