Utilization of the energy and protein of the same diet by cattle of different ages

Abstract

Most calorimetric experiments to determine the value of feeds as energy sources are made with mature animals. The question arises whether the energy values of feeds determined with them apply equally to young growing animals, but there is little information to answer it. Ritzman & Colovos (1943) determined the energy retention of cattle throughout their growing period. Their results were recomputed to find whether the efficiency with which the metabolizable energy consumed in excess of their maintenance needs was used by growing animals to promote energy retention differed from that to be expected from independent experiments made with adult cattle. Excellent agreement between the observations of Ritzman & Colovos and expectations based on results obtained with adult animals was noted when the animals were almost full-grown, but with animals weighing 200 kg. or less agreement was poor, younger animals apparently being more efficient than older ones. Such an effect of age on efficiency might be accounted for by a change with age in the ratio of protein to fat deposited in the body, for it seems likely that protein synthesis from absorbed amino acids is a more efficient process than is the synthesis of fat from the oa;o-acids formed from them.The evidence of Ritzman & Colovos, (1943) experiments that young animals are more efficient in using metabolizable energy for body synthesis than are old ones is, however, indirect: the diets given to the animals changed with their age and general equations had to be used to calculate maintenance needs and expected efficiencies above maintenance. The experiments described below were undertaken to provide more direct evidence about the effect of age on the efficiency of energy utilization by feeding the same diet to cattle of different EXPERIMENTAL Animals. Seven Ayrshire steers numbered 1-7 were used. They were reared on whole cows' milk, weaned when 7 weeks old and thereafter given a * Present address: Rowett Research Institute, Bucksbum, Aberdeen. diet of hay and a commercial cattle-rearing pellet in amounts sufficient to result in steady growth. The animals were castrated as soon as the testes had descended.Experiments. Five experiments, each with three steers, were made. Exps. 1, 2 and 3 were made with steers 1, 2 and 3, commencing when they were 31, 46 and 81 weeks of age. Exp. 4 was made with steers 4, 5 and 6, commencing when they were 15 weeks of age, and Exp. 5 with steers 4, 5 and 7 when they were 35 weeks of age.Each experiment began by each animal being fasted for 4 days to determine its fasting energy metabolism. The steers were then given the experimental diet in increasing amounts for 1 week, or until such time that a normal intake of feed was re-established. Each animal was then given three different amounts of the diet in successive 3-week periods, the sequence of treatment for the three animals in an experiment conforming to the rows of a latin square. During the last week of the periods energy and N metabolism were measured. The amounts of feed given varied...

A study of the energy requirements of weaned lambs

“…calculated. The daily quantities of nitrogen retained were 1-8 and 1-5 g for Experiments 1 and 2 respectively and compare with a pooled value of 1-8 g obtained by Blaxter, Clapperton and Wainman (1966) for young cattle. The nitrogen retained was first expressed per unit DOMI and then adjusted to the mean maintenance DOMI presented in Table 5.…”

Prediction of the Energy Requirements for Growth in Beef Cattle 1. The irrelevance of fasting metabolism

“…It remains however a moot point whether ME is used with the same efficiency for growth as for fattening. Blaxter, Clapperton and Wainman (1966) were unable to detect changes with age in k f measured in successive calorimetric trials with growing cattle. More recent work suggests however that in monogastric animals the efficiency of utilization of ME for growth does vary according to the partition of retained energy between protein and fat (Schiemann, 1970;Pullar and Webster, 1974).…”

Effects of isolation, confinement and competition for feed on the energy exchanges of growing lambs

“…Blaxter et al (1966) estimated the magnitude of errors likely to arise from changes occurring in the body weight of animals during the evaluation of the net availabilities of the metabolizable energy of a feed for maintenance (k m ) and for fattening (k f ) using the classic incremental approach. Blaxter et al (1966) estimated the magnitude of errors likely to arise from changes occurring in the body weight of animals during the evaluation of the net availabilities of the metabolizable energy of a feed for maintenance (k m ) and for fattening (k f ) using the classic incremental approach.…”

“…This stability of body weight is important to the accurate prediction of net availabilities (Blaxter, Clapperton and Wainman, 1966). Such animals are accustomed by repeated exposure to the experimental procedures employed.…”