Effects of different forages on production of hydrogen sulphide in a rumen in vitro system

Sammanfattning: The purpose of this project was to use a new in vitro method to estimate rumen protein degradation (proteolysis) in a series of fresh forages and silages. The new in vitro technique is less invasive than existing protein degradation techniques (nylon bag incubations in fistulated cows), and is easy to perform. The technique builds on the in vitro gas production technique and is based on the fact that sulphides- particularly hydrogen sulphide (H2S)- are important products from rumen proteolysis. Four experiments are included in this report and they were set up at IGER, Aberystwyth, U.K. One of the experiments included freeze dried silage and three were conducted with fresh herbage (grasses or legumes). One study looked at effects of different species and varieties of grass (Cocksfoot, Meadow Fescue, Ryegrass, Tall Fescue and Timothy) and the legume Lotus spp. Investigations of the effect of wilting time were made by studying ryegrass wilted for 48, 24, 12, 3 and 0 hours. The third study looked at the effects of silage additives. Untreated silage was compared to silage prepared with formic acid, and silages prepared with inoculants containing lactic acid bacteria ('Power Start' or 'Pioneer'). The work also included an investigation of the effects of tannin levels in Lotus spp. on the production of H2S. In each experiment, the plant material was incubated with rumen fluid for 12 hours. Measurements of H2S production were made 2, 4, 6, 8 and 12 hours after the start of incubations. The amount of H2S formed was also compared to the crude protein content of the plant material. It was shown that Lotus spp. produced significantly lower levels of hydrogen sulphide than grasses. In the experiment where the effect of wilting duration was studied, there was no significant difference between samples when the total production of hydrogen sulphide was measured. However, when comparing the amount of H2S formation to the crude protein content of the plant material, grass wilted for 48 hours had significantly lower H2S production. In the experiment comparing different silage additive treatments, the untreated silage had significantly lower production of H2S than the other silages. When studying the effect of tannins, it was showed that Lotus, containing the highest levels of tannins, produced larger amounts of H2S than the other varieties. The in vitro gas production technique used in this work was easy to work with and some of the results were similar to the literature but unexpected differences were also observed. In the experiments studying the effect of inoculants in silage and the tannin content in Lotus, the results differed from the literature. Analysis of sulphides might not be a reliable measurement of protein degradation in the materials because of the reaction of H2S with hydrogen cyanide produced when cyanogenic tissues are damaged. These results emphasise the importance of further research and evaluations to improve the accuracy of the in vitro H2S production technique.