Quantitative assessment of enteric methane emission and nitrogen excretion by equines

Abstract

In France enteric methane emission (CH4) in horses have been assessed using the net energy requirements of equines expressed in feed units (UFC) and converted to Digestible Energy (DE) intake using prediction equations from the UFC system. Methane emissions were then calculated from DE intake using a prediction equation of methane expressed in percent of DE intake (ECH4 % DE). Emissions of methane have been assessed for the different categories of equines in respect of their physiological status and the main types of diets at through or grazing using UFC recommended allowances form INRA, 1990 and average composition of diets used in France. Methane emissions averaged 20.7 kg/animal/year whatever the type of equines but the highest value was 29.4 kg for heavy mare reaching 34% of the emission estimated of a beef cow. Models of prediction of N excretion in faeces and urine of equines have been established from experimental data obtained when measuring digestibility by total collection of faeces and urine and nitrogen balance experiments carried out at INRA. Models for prediction of N faecal or urinary excretion used both N intake as a predictor: R2=0.866 and 0.716 respectively. But reliability and accuracy of N Urinary excretion were improved when using DM intake and N content of diets as predictors (R2=0.824). Annual total N excretion in faeces and urine for a 500 kg BW adult horse at maintenance would amount to 238 kg CP/animal that is to say 38 N units of which about 50% would be supplied by faeces and 50% by urine Assessment of total N excretion of the different categories of equines is in progress. Horse and ponies will be evaluated in respect of physiological status and diets for the French population as for methane emission.