Arachis oil was added to heavily wilted herbage of approximately 40 dry matter, bejore ensiling in polyethylene containers. The oil was added at a mean level of 4 9 16% of the total dry matter ensiled. The mean dry matter loss from the two control and the two oil-treated silages was approximately 13%. There was a lower loss as inedible waste in the oil-treated silages and mould growth appeared to be inhibited by the oil. There was a lower percentage of butyric acid and propionic acid in the oil-treated silages than in the control silages, this effect being statistically significant. Ensiling resulted in a greater fall in digestibility of the control material than in the oil-treated material. The oil-treated silages had higher metabolisable energy contents than the control silages but the dry matter intakes o,f both silages by sheep were low.Introduction THE conservation of grass as silage has several major disadvantages. The high dry matter losses are perhaps the greatest disadvantage, and in recent years it has been shown that the use of synthetic films to exclude air will greatly decrease the dry matter losses from the sil0.l-7 Also, the digestible energy content of silage is commonly fairly low. In a previous experiment8 it was found that silage produced by the addition of 4.9% arachis oil (on a dry matter basis) to wilted grass, had a higher metabolisable energy ( M E ) than control silage, and that the silage produced was of satisfactory quality and readily eaten by dairy cows and bullocks. The results suggested that there was no appreciable change in the composition of the fatty acids present in the arachis oil while the material was in the silos.Hoffmann et al.9 found that arachis oil increased methane production by cattle and sheep in the rumen. A considerable number of further experiments have been carried out on the fate of vegetable oil or fatty acids in the ruminant and their effect on the utilisation of dietary energy by ruminants.10-17 These latter experiments have shown that dietary or infused linseed oil or fatty acids led to a marked reduction in the production of methane, the effect being greater with unsaturated than with saturated fatty acids. Czerkawski ef aI.lo found that when fatty acids were infused into the rumen, the reduction in energy loss as methane was greater than the incfeased loss of energy in the faeces with the result that the ME of the fatty acids was 104% of their heat of combustion. Their results and their reinterpretation of the results of other workers, some of whom used arachis oil,gJS led them to conclude that long-chain fatty acids arising from lipids, when absorbed by ruminants, are utilised with an efficiency much the same as that found in non-ruminant animals, i.e. about 80%, and retained by the body as fat. This suggested that the fatty acids, once absorbed, were not broken down to any appreciable extent, but were incorporated directly into the lipids of the tissues.The results of the above investigations, mainly published since the results of the original experiment...
