THE BENEFICIAL-EFFECTS OF A MICROBIAL FEED PHYTASE IN DIETS OF BROILER-CHICKENS AND DUCKLINGS

Experiments with growing chickens and ducklings were designed to test the efficacy of a microbial feed phytase in releasing phosphorus (P) i n diets based on sorghum and soybean meal. CaHPO4 was added in signifi cant amounts to two of the five diets (4 and 5). For chickens, there w as an overall improvement with phytase addition of P retention of 18%. Growht rate, feed intake, feed efficiency, nitrogen retention, tibia ash and tibia P all showed a significant improvement. Benefits tended to be less or not at all on the two diets (4 and 5) with added CaHPO4. For ducklings, overall improvement with phytase additions on P retent ion was 29%. On diets without CaHPO4, tibia ash, feed intake and growt h rate but not FCR were improved. Diets 4 and 5 showed fewer or no res ponse to the addition of phytase. Using a slope-ratio assay and bone a sh (g) as the criterion of response, availability of P for ducklings i n soybean meal was 58%.