Dietary self-selection and the regulation of protein and energy intake in chicks

Self-selection of dietary protein and energy by broilers grown under a tropical climate: adaptation when exposed to choice feeding at different ages

Three hundred broiler chicks (Hubbard) of both sexes were assigned to five feeding treatments: T0 received a complete diet (control), T1 was a choice feeding system with simultaneous access to an energy-rich feed (ground corn) and a protein concentrate (43.7% CP), and T2, T3, and T4 were introduced to choice feeding after 1, 3, and 5 wk, respectively, of consuming the complete diet. At 1-d-old, T1 chicks showed a marked preference for corn, with only 21.4% of their intake being the protein concentrate diet. Intake of the concentrate progressively increased to 40 to 45% after 3 d of adaptation, resulting in diets with 22.5 to 24.3% CP. When broilers fed the complete diet for 1 to 5 wk (T2, T3, T4) were changed to choice feeding, on the 1st d, their feed choice intake was similar to that of T1 chicks at the same age. Visual observation and tactile assessment of the feed particles during the initial period allowed the chicks to quickly evaluate the new feeds and to adapt their feeding behavior. Although total feed intake to 6 wk of age was not significantly affected by the feeding treatments, broilers on choice feeding selected diets with a lower percentage of CP and had lower live body weights at 6 wk than those fed the complete diet (T0).

Dietary self-selection vs. complete diet: body weight gain and meal pattern in rats

Food intake and body weight gain of male adult Wistar rats were examined in two groups of animals. One group (n = 14) was allowed to select its diet from separate sources of protein (casein, 3.1 kcal/g), fat (lard and sunflower oil, 7.9 kcal/g) and carbohydrate (CHO, starch and sucrose, 3.3 kcal/g). Another group (n = 10) received a nutritionally complete diet (3.3 kcal/g). After 2 weeks of adaptation to the diets, body weights and meal patterns were recorded for at least 4 days. The total caloric intake was nearly identical for the two groups of rats. Rats given dietary choice gained less weight over 4 days than rats fed chow and showed reduced feed efficiency. During the 24-h period, self-selecting rats consumed 20.8% of calories as proteins, 21% as fats and 58.2% as CHO. Self-selecting rats ate significantly less calories during the day than did rats given chow. The chow diet consisting of 17.3% calories as protein, 7.6% as fat and 75.1% as CHO. When comparing the self-selecting group nutrient intakes to those of chow-fed group it was observed that 24-h protein calorie intakes were identical in both groups. Fat intake was significantly higher and CHO reduced as compared to chow-fed rats. During the day, CHO intake was higher in self-selecting rats, and fat intake was not significantly reduced. During the night, protein and fat intakes were significantly higher in self-selecting rats, while CHO intake was significantly decreased, particularly in the last periods of the night.(ABSTRACT TRUNCATED AT 250 WORDS)

Sparrows discriminate between diets differing in valine or lysine concentrations

White-crowned Sparrows (WCS) were given free access to pairs of semisynthetic diets that were either adequate or subadequate (25% of requirement) in valine or lysine. Within 2 to 4 days WCS chose a ratio of the paired diets that allowed them to maintain body mass or restore any losses quickly. On the initial choice days the birds transiently reduced total daily food intake (TDFI) roughly in proportion to their intake of the subadequate diet. The initial decrease of TDFI was greater and the latency in choosing an effective ratio of the paired diets was 2-3 days longer with valine than with lysine diets in well-nourished test birds. In malnourished birds fed only the subadequate test diet for 3 days, valine-deficient birds increased TDFI and body mass more promptly than did lysine-deficient birds when offered a choice of adequate and subadequate diets. The form of the test amino acid (CAA = crystalline, PB = protein-bound) had little effect on choice behavior, but sudden transfer of WCS from a PB acclimation diet to test diets with a large total CAA concentration increased the latency of effective choice by 2-3 days. A brief acclimation (2-3 days) to a CAA diet precludes any bias between nutritionally equivalent CAA and PB diets. The small differences in choice dynamics between valine and lysine and between dietary forms may help to identify mechanisms involved in food choice but are probably ecologically insignificant to free-living WCS. These birds are very adept at selecting diets that satisfy their amino acid requirements.