High doses of vitamin E and vitamin C influence in vitro rumen microbial activity

An evaluation was undertaken to determine if the antioxidants vitamin E and vitamin C affect gas (GP) and volatile fatty acids (VFA) production, and microbial N growth (MN) when incubated with fibrous or starchy feeds for a substrate specific incubation time (t1/2; the time at which half of the asymptotic GP is reached). Meadow hay and corn grain were preliminarily incubated for 144h, and t1/2 was determined to be 16 and 9h, respectively. Thereafter, 0.50 g of the two feeds, supplied with 0 (control) or 8 mg/g feed of alpha-tocopheryl acetate (vitamin E) or L-ascorbic acid (vitamin C), were placed in bottles with buffered rumen fluid in four replications and incubated for t1/2. The cumulated GP and VFA yields were measured and MN was computed from an ammonia-based N balance as described in the literature. Despite common antioxidant properties, the two vitamins had differing influences on the rumen metabolism for almost all the fermentation parameters. Vitamin E decreased MN when supplied to hay (-36%) but not when supplied to corn (feed x vitamin interaction; P=0.024). Vitamin C increased GP by 21% (P<0.001), and nominally increased +10% VFA (P=0.09), and +6.8% MN (P=0.09) in comparison to the control, irrespective by the feed used. It was concluded that high doses of vitamin E impairs microbial activity when used on fibrous feeds but not when used on starchy feeds, whereas vitamin C, irrespective by the feed used, exerts positive effects on microbial activity, but the effect is of small relevance. (C) 2013 Elsevier B.V. All rights reserved.