Effects of Native or Exogenous Benzoxazinoids on In Vitro Ruminal Fermentation and Degradability of Either Fresh or Ensiled Whole‐Crop Maize‐Based Diets in Cattle

Benzoxazinoids (BXs) are secondary plant compounds and an important part of the plant's defence system against herbivore attacks and microbial pathogens in maize. Whole-crop maize represents a common feed for ruminant livestock and is most commonly fed as silage, a conservation process that promotes the conversion of BXs into the potent downstream metabolite 6-Methoxy-benzoxazolin-2(3H)-one (MBOA). Possibly, the antimicrobial impact of BXs may not be restricted to plant pathogens but could as well affect the rumen ecosystem, which, however, has not yet been investigated. The present study analysed the effects of a low and a high BX maize genotype, either in fresh or ensiled form, on the in vitro ruminal fermentation and the degradability of main proximate nutrients using a rumen simulation technique. Moreover, the addition of exogenous MBOA when incubating the low BX maize genotype was tested. The data obtained showed no differences in ruminal fermentation variables, such as pH, short-chain fatty acids, gas production and gas composition. Likewise, the incubation of high BX maize genotype or the addition of exogenous MBOA did not affect the substrate degradability. The ensiling of maize slightly increased the degradability of certain proximate nutrients when compared to fresh maize, which, however, should not be related to maize genotype or exogenous MBOA. No detrimental impact of BXs on the in vitro ruminal fermentation were found and based on this, future studies may then focus on potential absorption and subsequent impact of BXs or its derivatives on the animal in long-term.