Incidence of dietary viscosity on growth performance and zinc and manganese bioavailability in broilers

Two experiments were carried out to study the effect of dietary viscosity on Zn and Mn tissue deposition and on performance of broiler chicks (21 days of age, 2 x 80 chicks). In Experiment 1, the basal diet (37 mg/kg Zn and 29 mg/kg Mn), was supplemented with two levels of Zn (14 and 35 mg/kg) and Mn (16 and 40 mg/kg) in the presence or absence of Guar Gum (GG) (0.375%). In Experiment 2, the basal diet (34 and 31 mg/kg Zn and Mn, respectively), was supplemented with two levels of Zn (10 and 30 mg/kg) and Mn (12 and 35 mg/kg) with or without GG (0.75%). Growth performance of chicks was not modified by Zn and Mn levels neither by the dietary addition of 0.375% GG. Adding 0.75% GG reduced growth, feed intake and increased feed conversion ratio. Similarly, tibia ash percentage was lowered when 0.75% GG was added to the diet. Zn and Mn tibia concentrations and Zn concentration in plasma increased with Zn and Mn dietary levels. Tibia and plasma Zn concentrations were decreased in the presence of 0.75% dietary GG. In contrast, tibia Mn concentration tended to increase (statistically NS) when GG was added to the diet. The present investigation shows that high dietary real applied viscosity (RAV) (6.80 ml/g) decreases growth performance and Zn availability in the young (21 days) chicks. Therefore, introducing highly viscous raw materials such as triticale, rye or barley at high levels in chick diets may contribute to increased Zn level in poultry manure. (C) 1999 Elsevier Science B.V. All rights reserved.