Abstract Samples of Kikuyu grass (Pennisetum clandestinum) from 19 farms located in five municipalities in the Antioquia Department of Colombia were analysed for proximate constituents and for the principal end productos of the...
moreAbstract
Samples of Kikuyu grass (Pennisetum clandestinum) from 19 farms located in five municipalities in the Antioquia Department of Colombia were analysed for proximate constituents and for the principal end productos of the fermentation determined in vitro incubations with rumen fluid.
The chemical composition and rumen fermentation parameters varied between the samples from the different municipalities, but there was no relationship between the main indices of ruminal fermentation (molar ratio of propionic:acetic acid and methane) and the key parameters of the chemical composition (crude protein, in vitro digestibility, neutral detergent fiber) of the dry matter of the samples of Kikuyu grass. There were marked differences in the methane content in the gas at 24 and 48h , with twice the concentration found at 48 than at 24 hours. Per unit of original substrate, methane production at 24h was 60 % higher compared to the production per unit substrate digested, whereas at 48h the difference was only 10%. These results indicate that the increased production of methane at 48 h compared to that at 24h was because most of the production of methane at 48h was deriuved from acetic acid according to the secondary fermentation pathway, rather than by fermentation of the original substrate.
The implications of these results are that in vitro incubations, intended to simulate the conditions within a ruminant animal, should not extend for much more than 24 hours, because at 48h the conditions relate more to those in an anaerobic biodigester.
Key words: digestibility, incubation time, metabolizable energy, methane, ratio propiónic:acetic acids, VFA
