Abstract
Total 1, 320 one-day-old chicks of 4 pure- and 4 cross-brees were used in 8 experiments, in which chicks were divided into 9 lots and fed one of the 9 experimental chick starter diets for 4 weeks and one of 9 experimental chick finisher diets for another 4 or 6 weeks. The starter diets contained one of the 9 combinations of 3 levels of dietary total digestible nutrients (TDN), i.e., 83, 73 and 63%, and of 3 levels of dietary protein, 26, 22 ane 18%. The finisher diet contained the same level of energy as but 2% lower protein than those of the corresponding starter diet.
Individual body weight and feed intake as a group were measured once a week, but only the data at 4, 6, 8 and 10 weeks of age were analyzed statistically. The following conclusions were obtained:
Growth responses of the chicks of all the breeds tested at 4, 6, 8 and 10 weeks of age to the change in dietary energy and protein levels were described well by surface of elliptic paraboloids, which were given by quadratic equations (1)-(8).
Based on the response pattern of body weight gain, 8 breeds tested were grouped into 2. One was meat-type breed, whose characteristic was to have sharper response to the change in dietary energy and protein levels than the responses of the other group, eggtype breed. White Cornishes (WC), White Plymouth Rocks (WR), WC×WR, WC×NH (New Hampshires), and WC×WL were included in the meat-type. White Leghrons (WL), Barred Plymouth Rocks (BR) and WL×BR were grouped into egg-type.
Actually no breed difference was observed at various ages on elliptic paraboloid response pattern of body weight gain per unit feed intake, i.e., feed efficiency. The finding suggested that the apparent breed difference in the response pattern of body weight gain itself could be attributable to the difference in the ability to take condensed diet among the breeds of chicks.
Partially differenciating the elliptic paraboloid equations, it was estimated that the dietary protein level to get maximum response with a certain dietary energy level was about 24-26% at 4 weeks of age and about 22-24% at ages older than 4 weeks. It was suggested that the optimum dietary protein level could be cut down by 2% after 4 weeks age.
