Short-term effects of food protein content on subsequent diet selection by chickens and the consequences of alternate feeding of high- and low-protein foods.

1. Growing male chickens of broiler and layer strains were allowed to eat either a high-protein food (HP) or a low-protein food (LP) for 10 min after an overnight fast and then offered a choice between HP and LP. During the next hour they ate significantly more of the food other than the initial meal. Similar results were obtained when there was a gap of 45 min without food between the initial meal and the choice period. 2. When the initial meal was given by tube into the crop, followed by 45 min without food, there was no significant effect on subsequent diet selection. These results show that it is necessary for the birds to eat the food themselves for it to exert its effect on subsequent choice. 3. Birds with experience of eating two foods identical in nutrient composition but different in colour did not select either food in preference to the other following an initial meal of one alone. This is evidence against the possibility that neophagia accounts for the results of the first two experiments. When an initial meal of low protein food was followed by a choice of high and low protein foods, birds ate a greater proportion of the high protein when it was placed on the opposite side of the cage from that in which the initial meal was given. Thus they are not choosing a food simply by its position within the cage. 4. To see the extent to which broilers can extend their ability to compensate for protein content over several weeks, male broilers were given one of 4 treatments from 5 to 10 weeks of age: (A) HP and LP concurrently; (B) HP and LP on alternate days; (C) HP in the morning and LP in the afternoon, (D) LP in the morning and HP in the afternoon. There was no significant effect of treatment on food intake, body weight gain or carcase protein content but carcases were significantly less fat after treatment (B) than treatment (D). 5. It is concluded that growing broiler chicks can compensate well for periods of access to only a low-protein food, by subsequent intake of high-protein food, and vice versa, as long as they are able to gauge the sensory properties of the foods. Offering two complementary foods in alternating half-day periods is an effective method of choice-feeding, allowing birds to select a diet to meet the requirements for growth.