Choice Feeding Experiments with Growing Pigs

The amino acid requirements of growing animals are predicted to change with time, due to changes in the requirements for maintenance and for growth. Because food intake also changes with time, the question of optimising the dietary concentrations of a m i n o a c i d s d u r i n g t he g rowing period of animals is difficult to rcsolvc w i t h o u t resorting to computer mod&. Even such models cannot always accurately predict changes in day-to-day variations in temperature, gcnotypc, sex, food consumption, etc. As alternatives to a single feed system, where no account is taken o f t h e s e c h a n g i n g requirements, the possibility exists of altering the proportion of protein in the feed as the growing period proceeds, a system known as phase feeding; or of allowing growing animals free access to two feeds varying in protein concentration. This latter system, choice feeding, has been found to be successful with chickens and rats, and the ser ies of experiments reported here indicates that pigs, too, have the ability to differentiate between two feeds differing not only in protein content, but also in energy content.