Dietary manipulation to reduce methane production from ruminants and the impact on milk fatty acid profile

Methane is one of the greenhouse gases that causes global warming and has been listed for reduction within the UK. Under the UK climate change act (2008), the UK is committed to reducing GHG emissions by 80% against the 1990 baseline by the year 2050 with a minimum of 34% reductions to be achieved by the year 2020. This thesis pres ents results of assessments of various d ietary manipulations including use of starch sources, use of oil sources and grazing with or without supple mentation on methane production and productivity and the imp act on milk fatty acid profile in dairy cows. The in vitro study was initiated to assess the effects of starch and oil source on in vitro fermentation characteristics and methane production. Resul ts showed that the three starch sources, wheat , barley and maize differed in their cumulative and r ate of gas production. Wheat produced the highest and maize the lowest cumulative and rates of gas production. Methane production did not diff er among the st arch sources. Among the oil sources, carva crol, linseed oil and fish oil when added at the same level of supplementation differed in fermentation characteris tics and on methane production. However , when methane production was expressed per time of incubati on , variation s in me thane production were observed when compared to the control . Carvacrol reduced methane production by 50 - 80% at all time periods while linseed oil only reduced methane production by 20% at 36 - 48 hrs of in vitro incubation and fish oil ei ther had no effect or increased methane production. Results of the in vitro study were used to establish the treatments for the first in vivo study. The e ffect s of starch and oil source on methane production, productiv ity and milk fatty acid profile in dai ry cows were examined in a 4X4 Latin square design. Wheat and maize based concentrates w ere used as starch sources and M egalac and sunflower oil were used as oil source s . Sunflower oil was not effective at reducing methane production in cows, but did alter the milk FA profile by increasin g the PUFA content and reduced the palmitic acid content. Maize based concentrates were effective in reducing methane output when results were expressed as g/d and g /kg milk yield and improved the energy balance of the cows as evidenced by the positive condition score change , and also reduced plasma 3 - OHB concentration. T he starch and oil source acted independently, with no interaction observed on methane production and milk FA profile. The third experiment was a grazing tr ial which examined the effect of time of pasture access with or without TMR supplementation on methane production, productivity and milk fatty acid profile of high yielding dairy cows. Grazing , regardless of the time of access , reduced methane production w hen expressed as g/kg DM intake and g/kg milk yield. P roductivity of cows that grazed during the day with access to TMR was similar to continuously housed animals, while in the rest of the grazing groups, milk production was lower. Grazing also increased t he long chain FAs in milk fat and reduced concentration of palmitic acid. In conclusion, a variety of dietary manipulations can have a significant imp act in reducing methane emissions . Conclusions drawn from the project are that, m aize as opposed to wheat based concentrate s r educe methane production and improve s condition score of the cows. Purified sunflower oil supplementation reduces intake, d oes not reduce methane production but improves the fatty acid profile of the milk. When grazing high yielding cow s, grazing during the day with TMR supplementation is recommended as this does not compromise milk production. Methane production per unit of DM intake and per unit of milk yield is lowered regardless of the time of grazing.