Do fats reduce methane emission by ruminants? - a review

In recent years, methane has been one of the most discussed and researched subjects due to its effect on global warming and climate change. Approximately 60-65% of methane production is of anthropogenic origin. Considering that half of this volume is generated by livestock breeding, both breeders and nutritionists show significant interest in this matter. Biotechnological and immunological methods as well as genetic improvement studies have the potential to reduce methane emission from ruminants, but as yet they are not commonly applied. For this reason, feeding strategies that are easier to implement in practice are being considered as having the potential to increase the effective usage of consumed energy while decreasing global methane emissions. Adding fat to the diet of livestock will reduce the amount of carbohydrate consumed. It is known that fats reduce the number of protozoa, while some of the unsaturated fatty acids compete with methanogens for hydrogen. Therefore fats, oilseeds and fatty acids have been intensively studied to see whether they can reduce methane emissions in practice. Although many of these studies have proven that certain fats and fatty acids may be used confidently and effectively, much in vivo research is still needed to clarify the most appropriate diet, which fats are the most effective, and the amount of fat/fatty acids required. In this review, the effect of using fats, fatty acids and oilseeds in ruminant nutrition is discussed in relation to enteric methane emission, rumen fermentation and the utilization of energy and selected nutrients.