In Vitro Estimation of the Effect of Grinding on Rumen Fermentation of Fibrous Feeds

SIMPLE SUMMARY: Intensive feeding systems for beef production are based on high proportions of concentrate at the expense of forages, which can lead to digestive disorders. However, the particle size of the different fibrous feeds can also affect the rumen fermentation pattern, and thus animal performance. Fermentation of six fiber sources (soybean hulls, sugarbeet pulp, palm kernel cake, oat hulls, dehydrated alfalfa meal, and barley straw) in two presentation forms (non-processed and ground) was studied in a closed batch in vitro system. Higher gas production was recorded when substrates were presented in ground form, except for barley straw; however, substrates ranked in the same order irrespective of their presentation form. The particle size did not markedly affect volatile fatty acids proportions. Methane production as an index of fermentation efficiency did not show major differences between feed presentation forms, or non-forage substrates as compared with straw and is related more with the magnitude of fermentation than with qualitative changes in fermentation. Considering other feed components, the comparison of substrates on rumen microbial fermentation depends not only on their fiber proportion but can also be mediated by their levels of protein and fat. ABSTRACT: The fermentation patterns of six fiber sources, soybean hulls (SH), sugarbeet pulp (BP), palm kernel cake (PK), oat hulls (OH), dehydrated alfalfa meal (DA), and barley straw (BS) were evaluated for this study on the effect of their presentation form (non-processed, NP and ground, GR). Substrates were tested in a conventional in vitro batch system, using rumen fluid obtained from ewes fed 0.5 alfalfa hay and 0.5 barley straw. All substrates rendered a higher gas production in GR form (p < 0.05) except for BS but ranked similarly irrespective of the presentation form. Among the substrates, when incubated NP, the highest volume of gas was recorded with BP from 8 h onwards (p < 0.05), whereas OH and BS resulted in the lowest gas volume (p < 0.05). During the first half of the incubation period, methane production was higher in GR than NP (p < 0.05). Among substrates, despite NP or GR, methane production with BP was the highest (p < 0.05). Similarly, the presentation form did not qualitatively affect fermentation, as no differences were observed in volatile fatty acids proportions. The effect of particle size of fibrous substrates does not have a major impact on the rate and extent of the rumen microbial fermentation.