ABSTRACTVoluntary food intake and body weight were examined over 4-week intervals between 14 and 70 weeks of age in 306 females from 25 British breeds of cattle. At each age, the relationship of the natural logarithm of voluntary food intake to that of body weight was examined by linear regression both within and between breeds.Of the total variation in voluntary food intake, the proportion accounted for by body weight was extremely high between breeds (phenotypically, 0·80 or more; genetically 0·88 or more, at most ages) but phenotypically low within breeds (0·33 or less). The mean voluntary intake of a breed at any age could be predicted from its mean body weight at the same age with a coefficient of variation (CV) among breeds that declined with age from 0·08 to 0·04. Within breeds, the corresponding CV for individual intake was between 0·12 and 0·15 beyond 9 months of age, and even higher at early ages.Within breeds, the regression coefficient of log intake on log body weight was close to the value of 0·7 at all ages. Between breeds, it was over 0·8 at early ages, declining to about 0·7 beyond 1 year of age. Thus, genetically larger breeds voluntarily consumed relatively more food at early ages compared with later ages. Breed size should therefore be taken into account when recommending food intake requirements. Breed deviations for high and low appetite are discussed.
The relationship between forage cell wall content and voluntary food intake in mammalian herbivores