Responses of broilers to dietary zinc concentrations and sources in relation to environmental implications.

1. Since high concentrations of zinc are associated with reduced crop yields, environmental concerns are emerging regarding zinc accumulation in areas where poultry production is prevalent. This study investigates growth performance and zinc utilisation during the life cycle of broilers when diets were supplemented with various concentrations of zinc from two different sources. 2. A total of 740 Cobb 500 1-d-old male broiler chicks was randomly distributed into 88 battery cages. Excreta were collected over a 48-h period on d 10, 17, 24, 31, 38, and 45 to measure zinc excretion on a dry matter basis. 3. During the 45-d experimental period, broilers were given a maize-soybean meal basal diet (30 mg/kg zinc) supplemented with 0, 20, 40, and 80 mg/kg of zinc from zinc sulphate, Availa Zn amino acid complex, or an equal combination of zinc sulphate and Availa Zn amino acid complex. 4. Progressive additions of zinc to the basal diet significantly increased body weight gain of broilers, but did not affect feed conversion or mortality. Optimum body weight gain was achieved at 80 mg/kg supplemental zinc, which exceeds the NRC recommendations of 40 mg/kg. 5. During each excreta collection period, increased supplemental zinc concentrations significantly increased zinc excretion. However, the zinc source did not influence zinc utilisation. 6. As compared with zinc sulphate supplementation, the cumulative zinc excretion data indicate that adding zinc to the basal diet in the form of Availa Zn amino acid complex decreased zinc excretion.

The expression of calbindin in chicks that are divergently selected for low or high incidence of tibial dyschondroplasia.

Three experiments were conducted with broiler chicks that were divergently selected for low or high incidence of tibial dyschondroplasia (LTD and HTD, respectively) to determine if the expression of intestinal calbindin-28 kD mRNA and protein differed between the 2 strains. In addition, levels of intestinal vitamin D receptor mRNA and plasma thyroid hormone concentrations were also examined. In experiment 1, LTD and HTD chicks were fed a corn-soybean meal diet that was adequate in all nutrients except cholecalciferol (D3), which was titrated to 5 or 40 microg/kg diet in a completely randomized 2 x 2 factorial arrangement. At 4 and 8 d of age, HTD chicks fed 5 microg of D3/kg of diet had a lower (P < 0.05) expression level of calbindin-28 kD mRNA than the LTD chicks fed the same diet. At 4 and 8 d of age, HTD chicks fed 5 microg of D3 had the lowest intestinal expression of calbindin-28 kD protein. Expression of vitamin D receptor mRNA did not differ for broiler strains at either level of D3 supplementation. In experiment 2, there was no significant difference in the expression of calbindin-28 kD mRNA or vitamin D receptor mRNA between day-of-hatch LTD, HTD, and commercial broiler chicks. Experiment 3 was similar in design to the first experiment except that the birds were fed for 18 d. Calbindin-28 kD and vitamin D receptor mRNA expression levels at 18 d were similar to those observed in experiment 1. Plasma triiodothyronine and free-triiodothyronine concentrations were greater for LTD chicks, regardless of dietary D3 supplementation levels. These results suggest that divergent selection of broilers for LTD or HTD alters the physiological response to nutritionally inadequate levels of dietary D3.