Conversion of the energy of the food into edible energy by two types of table poultry

Abstract

We have studied recently factors affecting the utilization of dietary metabolizable energy (ME) by table poultry (Davidson, McDonald, Mathieson & Williams, 1961 ;Davidson, Mathieson, Williams & Boyne, 1964). The criterion of utilization has been the total amount of tissue energy laid down by the bird over the experimental period. This gives an indication of the value of the diet for the bird but does not indicate the efficiency of conversion of the diet, or of the metabolizable energy in the diet, into food for human consumption.Because there was little information on this subject in the literature, especially for fast-growing strains developed recently in the United Kingdom, it was considered desirable to determine both total and edible energy in 3-34 lb birds of the Rhode Island Red x Light Sussex cross (RIR x LS) frequently used experimentally at this Institute, and also of a modern commercial fast-growing hybrid strain (Chunky Chicks Ltd, Newbridge, Midlothian) extracted from a number of breeds including New Hampshire, Rhode Island Red and Cornish. This was done in two experiments in which, incidentally, we were studying the effects of adding to the diet small amounts of those amino acids calculated to be most limiting for growth. E X P E R I M E N T A LThe experiments were designed to examine breed differences in total and edible energy, certain treatment effects mentioned below, and the breed x treatment interaction. Diets The starting diets, which were similar to diet H described in a previous paper (Davidson et al. 1961), contained 17% coarsely ground wheat, 45% ground barley, 18% Sussex-ground oats, 10% white-fish meal, 3 % maize gluten meal, 2% grass meal, 2 yo dried yeast, 0.5 % bone flour, I y', limestone flour, 0.5 yo common salt containing 24% MnSO,.qH,O, 0.15 yo of an antibiotic mixture (3.6 g chlortetracycline hydrochloride/lb ; Cyanamid of Great Britain Ltd, London), 0.05 % coccidio- I n each of the two experiments the starting diets were given until the chicks were 5 or 6 weeks old. After this, only one diet was offered because it was considered that any effects of supplementation would be evident by that time and would be reflected in subsequent growth even if supplements were discontinued. These finishing diets differed from the control starting diets in that 3 % barley was substituted for 3% white-fish meal. They thus contained about 2% less crude protein than the starting diets. T h e food eaten by each group was recorded weekly. Procedure I n both experiments 200 day-old cockerels of the RIR x LS cross and of the hybrid strain were given the control starting diet for 3 or 4 days and then weighed. Exceptionally light or heavy birds were discarded and ninety-six were randomized to eight groups of twelve birds. These groups were randomized to pens and to the experimental starting diets. T h e sixteen groups (eight of each strain) were housed in separate pens within the same hut, which was provided with background heating, and there were infrared lamps in each pen to give the increased tempera...