Renal energy excretion of horses depends on renal hippuric acid and nitrogen excretion

Summary The prediction of renal energy excretion is crucial in a metabolizable energy system for horses. Phenolic acids from forage cell walls may affect renal energy losses by increasing hippuric acid excretion. Therefore, the relationships were investigated between renal energy, nitrogen (N) and hippuric acid excretion of four adult ponies (230–384 kg body weight (BW)) consuming diets based on fresh grass, grass silage, grass cobs (heat‐dried, finely chopped, pressed grass), alfalfa hay, straw, extruded straw and soybean meal. Feed intake was measured; urine and faeces were quantitatively collected for three days. Feed was analysed for crude nutrients, gross energy, amino acids and neutral‐detergent‐insoluble crude protein (CP); faeces were analysed for crude nutrients and cross energy; urine was analysed for N, hippuric acid, creatinine and gross energy. Renal energy excretion (y; kJ/kg BW0.75) correlated with renal N excretion (x1; g/kg BW0.75) and renal hippuric acid excretion (x2; g/kg BW0.75): y = 14.4 + 30.2x1+20.7x2 (r = .95; n = 30; p