The effects of phytase supplementation on performance and phosphorus excretion from broiler chickens fed low phosphorus-containing diets based on normal or low-phytic acid barley

Abstract

A total of 240 day-old broiler chicks were used to study the effects of phytase on performance and phosphorus (P) excretion from birds fed diets containing low phytate barleys formulated without inorganic P. A positive control based on Harrington barley (HB) was formulated to meet requirements for total P. Three experimental diets, based on either HB (0.39% total P with 0.28% phytate P) or the low phytate varieties LP 422 (0.36% total P with 0.14% phytate P) and LP 955 (0.40% total P with 0.01% phytate P), were formulated to be below requirements for total P by removing all the inorganic P from the diet. The four diets were fed with and without 1,000 FTU/kg phytase. Apparent P digestibility was significantly higher (p<0.01) for birds fed the low phytate barleys than for birds fed HB either supplemented or un-supplemented with inorganic P. P excretion was significantly lower (p<0.01) for birds fed HB without inorganic P than with inorganic P. P excretion was further reduced by the use of the low phytate barleys LP 422 and LP 455 (p<0.01). Phytase supplementation did not affect P excretion (p = 0.39). Body weight gain and feed intake were highest for birds fed the HB diet with inorganic P and lowest for birds fed the HB diet without inorganic P (p<0.01). Among the three low P diets, body weight gain and feed intake of broilers increased as the level of phytate in the barley declined (p<0.01). Phytase modestly increased body weight gain (p = 0.08) and feed intake (p = 0.04). The overall results of this study indicate that it may be possible to reduce the amount of inorganic P used when formulating diets with low phytate barley compared with the levels needed when formulating diets with normal phytate barley. However, it is not possible to completely replace the inorganic P in diets containing low phytate barley without impairing poultry performance. Feeding diets devoid of supplementary inorganic P in combination with low phytate barley resulted in a significant reduction in P excretion by poultry.