Additivity of the effect of cereal and microbial phytases on apparent phosphorus absorption in growing pigs fed diets with marginal P supply

Cereal phytases originating from wheat and rye or in combination with supplemented microbial phytase (Natuphoso) each were added to phytase-inactivated cereal-based diets to determine whether phytases of different origin exhibit additivity in their response on coefficient of apparent phosphorus (P) absorption in growing pigs. Thirty castrates with an initial body weight of 16.5 kg were kept in stainless steel metabolism crates during a 20 days experimental period. The animals were allocated to six dietary treatments. The basal diets (Diets 1, 3 and 5) were devoid of phytase from wheat and/or rye due to complete inactivation of plant phytase in these grains by microwave treatment. Total phytase activity in the experimental diets was calculated to amount in total to 150 U/kg originating in equal parts from wheat and microbial phytases (Diet 2) of rye and microbial phytases (Diet 4) or wheat-and rye phytases (Diet 6). The diets were fed twice daily at a rate of 375 g per meal. An adaptation period of 10 days to the diets and experimental conditions was followed by a quantitative collection of faeces and urine during 10 days. The supplementation of phytase-inactivated basal diets with combinations of microbial and wheat phytases (Diet 2), microbial and rye phytases (Diet 4) as well as with wheat and rye phytases (Diet 6) increased (P < 0.05) coefficient of apparent P absorption by 0.179, 0.150 and 0.058 in the wheat-, rye- and wheat-rye-based diets, respectively. The linear regression model was used for predicting the additivity of the effect of each of the intrinsic (cereal) and extrinsic (microbial) phytases on apparent P absorption in growing pigs. It was concluded that different sources of phytases exhibit linear additivity in their response on apparent P absorption in growing pigs, provided that existing differences in equivalency values between cereal and microbial phytases, obtained under similar experimental conditions, are taken into consideration. (C) 2002 Elsevier Science B.V. All rights reserved.