Methane production from dairy cows : relations between enteric production and production from faeces and urine

Sammanfattning: Methane (CH4) is a greenhouse gas (GHG) that contributes to the global warming. One of the largest sources of methane is livestock, preferably ruminants which alone counted for 30% of the total agricultural anthropogenic methane emissions in the year of 2000. The reason to why ruminants are such large contributors of methane are that the gas is produced in the rumen by enteric formation and leaves the animals by belching, exhaling or by the excreta.Diets high in concentrates can result in a lower emission of methane. Also diets with a high content of starch, such as alfalfa-grass, have a methane-decreasing. It is profitable to reduce enteric methane formation since that form of methane is unavoidably lost. Methane emissions from manure, on the other hand, are possible to reduce during storage and manure-derived methane can also be collected and used as biogas fuel. It is earlier shown that it is possible by dietary means to compensate a reduced enteric methane production by a higher or maintained production of methane from manure.The hypotheses of this study is 1) that the feed regime with high percentage of pea/oat silage results in a lower emission of enteric methane compared to grass silage and 2) that this will result in maintained or higher methane production from the manure.In this study four rumen fistulated cows of the Swedish Red Breed was included. The cows where held in a separate part of a barn so that the sampling would not be disturbed by the other animals. The study was divided into four periods of one week each and two different treatments were tested; treatment A: 100% grass silage and treatment B: 25% grass silage and 75% pea/oat silage. All individuals were in each treatment twice during the study. Enteric methane was sampled once a day for five days in a row for each period. The gas samples were analyzed for produced methane and sulphur hexafluoride (SF6) and the amount of methane produced per day was then calculated by the methane:S F6-ratio. Faeces and urine was sampled during the first period and then analyzed for maximum methane producing capacity (Bo). Analyses were also conducted on dry matter intake, feed nutrient composition, the composition of faeces and urine and on produced milk.There was, as expected, a significantly higher starch intake in treatment B (25% grass silage, 75% pea/oat silage) than in treatment A (100% grass silage) (p=0.006). However, the diet with pea/oat-silage (treatment B) resulted in more methane per kg of ingested starch compared to the diet with grass silage (treatment A), opposite to what was expected. It could neither be shown that a reduction in enteric methane was followed by a higher or maintained production in methane from manure (faeces and urine). Contrary the difference in methane production was similar for enteric production and from manure. Further studies need to be conducted where a larger number of animals are included and the difference in starch content between diets is larger in order to be able to receive significant results.