title: Effects of mineral and rapeseed phosphorus supplementation on phytate degradation in dairy cows.
abstract: The objective of this study was to evaluate the effects of diet composition on phytate (InsP6) degradation in dairy cows. In Experiment 1, four diets that differed in the amount and source of phosphorus (P) were fed to 24 lactating cows in a 4 × 4 Latin Square design. The control diet (Diet C) contained 4.18 g P/kg dry matter (DM). Diet MP contained additional mineral P (5.11 g P/kg DM), Diet RS contained rapeseed and rapeseed meal as organic P sources (5.26 g P/kg DM) and Diet RSM contained rapeseed meal and rapeseed oil (5.04 g P/kg DM). Total P (tP) and InsP6 excretion in faeces were measured. In Experiment 2, we used a rumen simulation technique (Rusitec) to estimate ruminal disappearance of tP and InsP6 from Diets C, MP and RSM. In Experiment 1, tP concentration in faeces increased with tP intake and was highest for Diets RS and RSM. The source of supplemented P had no influence on tP digestibility, but tP digestibility was reduced for Diets MP, RS and RSM in comparison to that for Diet C. InsP6 disappearance decreased in Diet MP (85.0%) and increased in Diets RS (92.7%) and RSM (94.0%) compared to that in Diet C (90.0%). In Experiment 2, P source influenced ruminal tP disappearance (Diet MP, 78.6%; Diet RSM, 75.3%). InsP6 disappearance for Diet C (98.1%) was higher than that for Diets MP (95.6%) and RSM (94.9%). The results confirmed the high potential of ruminants to degrade InsP6, but differences in diet composition influenced InsP6 disappearance. Further studies of the site of InsP6 degradation are required to understand the relevance of InsP6 degradation for the absorption of P.
authors.affiliation: a Institut für Tierernährung , Universität Hohenheim , Stuttgart , Germany.
authors.forename: Eva
authors.initials: E
authors.lastname: Haese
authors.forename: Karin
authors.initials: K
authors.lastname: Müller
authors.forename: Herbert
authors.initials: H
authors.lastname: Steingass
authors.forename: Margit
authors.initials: M
authors.lastname: Schollenberger
authors.forename: Markus
authors.initials: M
authors.lastname: Rodehutscord
mesh_terms: D000821:Animal Feed / Q000032:analysis*; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D029741:Brassica rapa / Q000737:chemistry*; D002417:Cattle / Q000378:metabolism*; D004032:Diet / Q000662:veterinary*; D019587:Dietary Supplements; D004063:Digestion; D010758:Phosphorus / Q000737:chemistry / Q000494:pharmacology*; D010833:Phytic Acid / Q000378:metabolism*
chemical_list: D010758:Phosphorus; D010833:Phytic Acid
keywords: InsP6 degradation; feed formulation; mineral supplements; phosphorus; phytate; rapeseed oilmeal; ruminants