Zinc deficiency conditions food aversions in rats

[Estimation of the zinc requirement for broilers using their ability for selective zinc absorption and by dose-response relations]

Broiler chicks are able to select an adequate dietary Zn-concentration in choice-feeding. The zinc requirement should be ascertained by this method of self-selection. 72 day-old chicks were divided into 9 groups and were kept over 5 weeks in individual cages. By gradually supplementing ZnSO4.7H2O to a semisynthetic basal diet with isolated soybean protein 5 diets were made with Zn-concentrations of 14, 22, 30, 38 and 50 ppm, which respectively were fed to one group. The four other groups had to choose between two rations: 14/38; 14/50; 22/38; 22/50. Selective zinc intake was represented by a significant increase of dietary zinc concentration compared to random selection (mean of both diets). Feed intake, zinc intake and weight gain were measured daily and the end total feed consumption, live weight, feed conversion rate, plasma-zinc concentration and plasma-zinc binding capacity at the end of the experiment. In comparison optimal dietary zinc levels were estimated by dose-response relations, both by sigmoid growth curves and by broken-line model. With 30 ppm Zn chickens reached a high fattening level with daily weight gains of 60 g. Feed intake and growth rate were markedly reduced at a dosage of 14 and 22 ppm Zn, feed conversion rate was tendentially decreased below a level of about 34 ppm, whereas above zinc binding capacity reached a plateau. Birds self-selected a dietary zinc level of 32 ppm, which were adequate for the criteria feed intake and weight gains. Zinc requirements of about 40 ppm were assessed by conventional methods.

The role of experience in the development of selective zinc intake in pullets

Selective food intake behaviour was studied in pullets that were subjected to different zinc supply in early life. During the first four weeks post-hatching three groups, totaling 72 birds, were fed either a low zinc diet (25 ppm), a complete diet (50 ppm) or both diets in a choice situation. The prior feeding experience was investigated during the subsequent ontogenetic development in two-choice dietary tests. Chicks first exhibited a preference for the high zinc diet as deficiency symptoms can be seen in depleted birds. Juvenile pullets did not prefer any diet for the duration of experimental period. Layers were initially indifferent to the supplemented zinc diet, but after reaching high laying capacity they began preferentially to select the complete diet. The results indicate that early experience with diets different in zinc content have no influence on subsequent diet preferences at choice. The ability to select is based on association learning following ingestion. A conditioned diet aversion first developed in phases of high zinc requirement as a result of negative feedback mechanisms produced by the deficient diet.