Feed intake in chickens: genetic and social factors
The effects of genetic and social factors influencing ingestive behaviors, growth, livability, and dietary self-selection were investigated in three experiments. In Experiment I, ingestive behaviors, livability, and body weight were measured in lines of White Plymouth Rock chickens selected for high (HW) and low (LW) juvenile body weight reared in cages and floor pens as line-separate (S) and line-intermingled (I) flocks in three replicated trials. Body weights of Line HW chicks in cages, livability of Line LW chicks in cages, and ingestive behaviors of Line LW chicks in floor pens were higher in I than S flocks. Experiments II and III were designed to determine the ability of young chicks to discriminate among diets differing in amino acid content. In Experiment II, growth, feed intake, and feed preferences for diets varying in content of lysine, methionine, or tryptophan were measured in Line HW and a line of White Leghorns (HA) selected for high antibody response to sheep erythrocytes. Chicks were fed one of seven diets which were either balanced (Diet A), or slightly (1) or moderately (2) deficient in lysine (L), methionine (M), or tryptophan (T) for seven days. Chicks were then offered a choice between Diet A and the diet fed for seven days (3 to 10 days of age). Line HW chicks eventually showed a consistent preference for Diet A to all but Diet L1. For diet preference, interactions between time and diet were common in Line HW and the causes of these interactions were discussed. Line HA chicks preferred Diet A to M2, but otherwise did not choose between diets. Growth of Line HW chicks was reduced by feeding Diets L2, L1, and M2, but growth was not affected in Line HA. In Experiment III chicks from Lines HW, HA, and LW were provided a choice among diets with .85, .58, and .44 % methionine from one day of age. Line HW discriminated among diets with different methionine content from five days of age, but chicks did not make a consistent choice until after a period of deficiency. After a period of deficiency, Line HW chicks consistently chose the diet with .85 % methionine. Line HA chicks consumed more of the diet in slight excess of their methionine requirement and the reason for this is not clear. Line LW chicks did not discriminate among diets at any time during the trial. These results indicate that several factors interact to influence ingestive behaviors, growth, livability, and dietary self-selection in different genetic lines of chickens.