Impact and legacy of the highly cited paper by Blaxter and Clapperton (1965) ‘Prediction of the amount of methane produced by ruminants [Br J Nutr 19, 511–522]’

The paper by K. L. Blaxter and J. L. Clapperton (1965) ‘Prediction of the amount of methane produced by ruminants. Br J Nutr 19, 511–522’ has been cited 656 times according to Web of Science and continues to be cited with increasing frequency to the present day. The analysis described in the paper, or meta-analysis as it would be known now, is of methane production from cattle and sheep based on forty-eight trials using closed-circuit respiration chambers, all carried out at the Hannah Research Institute, Ayr, UK, between 1955 and 1965. Methane emissions per unit of diet fed were shown to vary depending on diet, level of feeding and individual animal. As such, previous notions that methane emissions were essentially proportional to energy intake were set aside. The main reasons for the paper’s continuing citation are the set of equations that can be used to predict methane emissions from ruminants when the technically demanding respiration chambers are unavailable, and that it was the first definitive study to describe the complexities of methane emissions with respect to animals and diets. The paper thus provided abundant insights of the relations between ruminant methane emissions and nutritional biology, and rumen microbiology, in particular, that have informed countless research projects in the intervening half-century. Given the importance of methane as a greenhouse gas in the climate change scenario, these insights are at least as relevant today as they were in 1965.