Universitiit Hohenheim, aInstitut fur Pflanzenernahrung -330-, and bInstitut fur Tierernahrung -450-, A rapid method is described for the colorimetric determination of 1.5-15 pg phytate phosphorus in concentrations as low as 3 pg ml-1 in extracts of cereal grains and cereal products. The phytic acid is precipitated with an acidic iron-111-solution of known iron content. The decrease of iron in the supernatant is a measure for the phyticacid content.

ZusammenfassungDer Einfluß von Calcium auf die Wirksamkeit mikrobieller Phytase in Rationen wachsender SchweineIn einem 3‐wöchigen Versuch mit 30 kastrierten wachsenden männlichen Schweinen (DLS x Pit; 6 Tiere/Gruppe; 16 kg Anfangsgewicht) wurde der Effekt steigender Calciumgehalte des Futters auf die Wirksamkeit eines Zusatzes mikrobieller Phytase [(1 000 U/kg) NatuphosR, BASF AG, Ludwigshafen, Deutschland) zur Verbesserung der Verwertung pflanzlichen Phosphors aus einer Gerste/Sojaextr. schrot/Sonnenblumenextr. schrot‐Ration untersucht. Die Versuchsdiäten enthielten dieselben marginalen Gehalte an Gesamt‐Phosphor [(4 g/kg),] Phytat‐Phosphor und von 5 auf 8 g/kg ansteigenden Calciumgehalte. Während der 10‐tägigen Vorperiode und der anschließenden 10‐tägigen Bilanzperiode wurden die Tiere in Stoffwechselkäfigen aus Edelstahl gehalten.Der Zusatz von 1 000 U/kg mikrobieller Phytase verbesserte signifikant die scheinbare Absorption und die Retention von Phosphor und Calcium. Ansteigende Calciumgehalte im Futter verminderten zunehmend die positive Wirkung des Phytasesupplements auf die scheinbare Absorption des pflanzlichen Phosphors. Allerdings wurde gleichzeitig die Verwertung des absorbierten Phosphors durch die ansteigende Calciumversorgung verbessert. Die höchste Verwertung des Nahrungsphosphors, und damit der geringste Verlust über die Exkremente, wurde bei 7 g Ca/kg Futter erreicht. Die Ergebnisse zeigen, daß die durch Zusätze mikrobieller Phytase zum Futter eintretende Verbesserung der Ausnutzung pflanzlichen Phosphors und die mit ihr verbundene Reduzierung des Phosphorausstoßes mit der Schweinegülle durch eine entsprechende Calciumversorgung weiter optimiert werden kann.

Two experiments with a total of 76 growing pigs (average initial body weight 16.6 kg) were conducted to compare the efficacy of cereal phytases (wheat and rye) and supplemented microbial phytase (Natuphos 1 ). Using the slope ratio technique, the dose-response relationship between five levels of phytase (0, 50, 100, 150 and 200 U kg À1 ) and the apparent absorption of phosphorus (P) within each source of phytase was calculated. Graded phytase levels in the diets were obtained by adding increasing amounts of microbial phytase or phytase-containing wheat (Exp 1) or rye (Exp 2) to phytase-inactivated basal diets at the expense of phytase-inactivated wheat (Exp 1) or rye (Exp 2). Except for wheat phytase, addition of phytase to the basal diets increased (P < 0.05) apparent P absorption, with microbial phytase being more efficient (P < 0.05) than cereal phytase. There were no significant differences in apparent P absorption between the wheat-or rye-based diets when either microbial or cereal phytases were supplemented from 0 to 200 U kg À1 . It could be derived from the results of this study, by means of regression analysis, that the efficacy of cereal phytases was 40% compared to microbial phytase.

Hydrolysis of phytate in the stomach and the small intestine as influenced by intrinsic plant (wheat) and supplemented microbial phytase (A. niger) were investigated with six minipigs (40-50 kg initial BW) fitted with re-entrant cannulas in the duodenum, 30 cm posterior to the pylorus (animals 1, 4, 5, and 6) and ileocecal re-entrant cannulas, 5 cm prior the ileocecal junction (animals 1, 2, and 3), respectively. Dietary treatments were as follows: (1) diet 1, a corn-based diet (43 U phytase/kg DM); (2) diet 2, diet 1 supplemented with microbial phytase (818 U/kg DM) and (3) diet 3, a wheat-based diet (1192 U/kg DM). At 0730 and 1930 per animal 350 g diet mixed with 1050 ml de-ionized water were fed. Digesta were collected continuously and completely during 12 h after feeding. In the duodenal digesta, 70% of the microbial phytase (diet 2) and 45% of the wheat phytase (diet 3) were recovered within 12 h after ingestion of the phytases, whereas only negligible amounts were detected in the digesta of pigs fed the phytase-poor corn-based diet 1. Most phytase activity passed through the stomach within the first hour after feeding. Microbial phytase activity at pH 2.8 was less sensitive to acidic pHs, such as those found in the stomach, than phytase activity at pH 5.3. Phytase activities in the digesta of the distal ileum did not depend either on source or amount of dietary phytase activity.

Developing grains were harvested from wheat plants grown in pots which had received additional late P‐fertilizer applications. By sequential extraction of milled grain samples of different developmental stages total P (Ptot) and the P‐fractions lipid‐P (Plip), phytin‐P (Pphy), inorganic and soluble ester‐P (Pi+e) and residual‐P (Pres) were determined.‐Due to the late P‐application, grain yield, Ptot, and Pphy content of ripe grains were increased by 14%, 58%, and 80% respectively, compared to the control. 93 % of the P which accumulated additionally in the grains as a result of the late P‐application, were found to be Pphy.‐During grain development the amounts of Ptot and Pphy per 1000 kernels increased steeply whereas those of Plip and Pres were not significantly affected by the stage of grain development or by the rate of P‐application. Pi+e increased during the first stages of grain development but subsequently decreased towards nearly the same low level regardless of the treatment.‐The increased phytin concentration in the ripe grains resulted in a decreased zinc bioavailability as was indicated by feeding experiments with growing male rats.