A FORMAL METHOD OF DETERMINING THE DIETARY AMINO-ACID-REQUIREMENTS OFLAYING-TYPE PULLETS DURING THEIR GROWING PERIOD

1. The amino acid requirements of laying type pullets during the growi ng period can be estimated by measuring the growth of different compon ents of the body and making use of nutritional constants that define t he amount of each amino acid that is required for the production of th e tissues being formed. 2. In this experiment, carcase analyses of eac h of three breeds of pullets were conducted at weekly intervals throug hout the growth of the pullets, to 18 weeks of age. Measurements were made of body weight, gut-fill and feather weight, and chemical analyse s consisted of water, protein, lipid and ash measurements of both the body and the feathers. Each age group comprised 10 birds of each breed . 3. Gompertz functions accurately estimated the growth of both body p rotein and feather protein, to 18 weeks of age, from which the rate of growth of these two components of the body could be estimated. The ma ture weight of pullets was overestimated by the Gompertz growth curve, which may indicate that a pullet ceases to increase in body protein c ontent once sexual maturity has been reached. 4. Using allometric rela tionships between the chemical components of the body and of feathers, all the components of growth could be estimated from the growth of bo dy protein and feather protein. These components were then added toget her to determine the growth rate of the body as a whole. 5. The daily amino acid requirements for 4 functions were calculated, namely, those for the maintenance of body protein and feather protein, and for the gain in body protein and feather protein. These requirements were then summed to determine the requirement of pullets on each day of the gro wing period. 6. Using the 'effective energy' system, the amount of ene rgy required by these pullets was calculated for each day of the growi ng period, from which the desired daily food intake of the pullets cou ld be predicted. By dividing the amino acid requirement by this daily food intake it was possible to determine the concentration of amino ac ids that would be needed in the diet in order to meet the requirements of a pullet. 7. The results indicate that the ratio between the requi rement for lysine and for methionine and cysteine changes dramatically during the growing period, negating the concept of a fixed ratio betw een all the amino acids during growth.8. The above process is the firs t step in determining the optimal feeding programme for a population o f pullets of a given genotype. The constraining effects, of the diet b eing offered and of the environment in which the pullets are housed, o n the food intake and growth rate of each pullet have to be estimated, and such a theory can then be expanded to include all the individuals in the population. Only by the use of simulation models can all these constraining effects be considered simultaneously.