Six breeds differing widely in body size and milk yield were compared for growth and food intake between 24 and 120 weeks of age in a time-controlled feeding system based on Calan-Broadbent electronic feeding gates activated by time clocks to give six meals a day of length 4, 5 or 6 min. The breeds were South Devon, Charolais × British Friesian, British Friesian, Hereford, Aberdeen Angus and Jersey. Each breed was represented by 12 animals, with four allocated to each meal length.
At every age, voluntary food intake was strongly determined by meal length. For each meal length, and after adjustment for breed size, most breeds closely followed the same intake curve. Thus, when intake was restricted (either slightly or severely) by uniformly limiting the time available for eating, the reduced voluntary daily intake of a breed, like its ad libitum intake, was largely genetically determined by breed size. A time-controlled feeding system thus allowed acceptable breed comparisons under conditions of restricted nutrition.
The mean growth rates resulting from a wide variety of different time-controlled voluntary intakes were all adequately explained by a linear equation based on a constant maintenance efficiency and a partial efficiency of growth that declined linearly with degree of maturity in body weight.
Eating rate was surprisingly similar for the three different meal lengths. When averaged over breeds, it increased from 1 MJ metabolizable energy (ME) per min between 6 and 12 months of age up to about 2 MJ ME per min at 2 years of age. Over this range, eating rate could be expressed as an allometric function of degree of maturity in body weight. In consequence, time-controlled daily intakes could be predicted from eating rate within ad libitum limits, as could the total eating time needed to achieve a given growth rate.