Submitted to: Poultry Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/8/2006
Publication Date: 2/1/2007
Citation: Linares, L.B., Broomhead, J.N., Guaiume, E.A., Ledoux, D.R., Veum, T.L., Raboy, V. 2007. Effects of Low Phytic Acid Barley on Zinc Utilization in Young Broiler Chicks. Poultry Science. v 86:299-308 Interpretive Summary: Most of the phosphorus in grains and legumes is found as a compound called phytic acid. Non-ruminant animals such as poultry, swine and fish, as well as humans, do not digest phytic acid well. In addition, dietary phytic acid binds tightly to zinc and other mineral nutrients. As a result, when non-ruminants consume grain and legume-based diets, they excrete most of the phosphorus consumed, and in addition, the dietary phytic acid has a pronounced negative impact on zinc nutrition. In this study chicks were fed diets prepared with either a normal barley, or a low phytic acid barley that contains only 5% of the phytic acid found in normal barley. In addition, each type of barley was supplemented with either no additional zinc, 10 mg zinc per kg diet, or 20 mg zinc per kg diet. The nutritional health of the chicks, with respect to zinc, was uniformly high when they consumed the low phytic acid diet as compared with the normal barley diet. While supplementation with zinc improved the zinc nutrition of the animals consuming normal barley, the animals consuming the low phytic acid barley still had better zinc nutrition. In addition, the chicks consuming the low phytic acid barley retained and utilized more of the dietary phosphorus than did chicks consuming the normal barley. This study clearly demonstrates that the use of low phytic acid grains and legumes both improves the utilization of phosphorus and important mineral nutrients like zinc.
Technical Abstract: Two 21 day experiments were conducted to evaluate the effects of low phytic acid barley (LPB) on Zn utilization by young broiler chicks, and to determine the contribution of endogenous phytase, present in LPB. In the first experiment, 96 d-old male chicks were assigned to a 2 x 3 factorial arrangement of treatments (4 pens of 4 chicks/trt). Factors were barley type (wild-type barley (WTB) and LPB mutant M 955) and supplemental Zn (0, 10 or 20 mg/kg Zn). In the second experiment, 240 d-old straight-run broiler chicks were assigned to a 2 x 2 x 3 factorial arrangement of treatments (4 pens of 5 chicks/trt). Factors were barley type (WTB and LPB), autoclave treatment (non-autoclaved or autoclaved (121oC, 20 kg/cm2, 20 min.), and supplemental Zn (0, 10 or 20 mg/kg Zn). Barley made up 60% of the diets and was the only source of phytate in the diets which contained on average 1.0% Ca, 0.45% non-phytate P, and 26 mg/kg Zn. Feed conversion and percent tibia ash were not affected (P > .05) by dietary treatments in either experiment. Feed intake and body weight gain were greater (P < .05) in broilers fed LPB compared to WTB in experiment 2. Zinc concentration in toes and tibias were affected (P < .0001) by barley type (LPB>WTB) and Zn level (20>10>0 mg/kg Zn), and significant barley type by Zn interactions were also observed in both experiments. Substitution of LPB for WTB increased tibia and toe Zn by 46 and 25%, respectively, an increase comparable to that achieved with 20 mg/kg Zn supplementation. No effect of autoclaving was observed for any variable in experiment 2. Retention of P and Zn were higher (P < .001) in chicks fed LPB compared to WTB in both experiments. Zinc retention was influenced (P < .0001) by dietary Zn, and barley type by Zn level interactions (P < .05) were observed in both experiments. Chicks fed LPB utilized more dietary Zn and P than those fed WTB, and this improved mineral utilization was not due to endogenous phytase present in barley. Key Words: Phytic acid, Barley, Zinc, Chicks, Autoclaving.