661. The genetic connexion between body size, milk production and efficiency in dairy cattle

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Abstract
1. An analysis has been made of production records and body measurements of dairy cattle from farms and special progeny testing stations in Denmark.2. Heritability estimates of various measurements of body size and also of gross efficiency of food conversion were all in the neighbourhood of 0·50. Body weight was more closely correlated with girth than with height.3. Milk yield had a very high correlation, both phenotypic and genetic, with gross efficiency. This was shown on theoretical grounds to be a necessary result of any standard system of feeding.4. Correlations between production characteristics and body measurements were slight. There was some suggestion that selection for yield would increase skeletal size but decrease fleshing.5. The best index on which to select for efficiency of food conversion under these conditions would be the yield divided by the height.