Replacing urea with nitrate as a non-protein nitrogen source increases growth and reduces methane production, while acacia tannin has no effect in lambs

Abstract

Abstract This study investigated the effect of urea or calcium nitrate with or without the inclusion of Acacia tannin extract on dry matter intake, nutrient digestibility, growth performance, and methane emission in growing lambs. Forty South African Mutton Merino lambs (95 days old, average body weight of 34.7\u202fkg) were blocked by weight and sex and randomly allocated to four groups and fed diets supplemented with: urea (control); nitrate; urea\u202f+\u202ftannin; and nitrate\u202f+\u202ftannin. The concentration of urea and nitrate source in the diet was 10\u202fg/kg and 32\u202fg/kg, respectively, while the tannin was an extract of Acacia mearnsii added at 42\u202fg/kg DM. Lambs were gradually adapted to the diets for 21 days after which growth performance was monitored for 60 days. At the end of the experimental period, methane was measured in open-circuit respiratory chambers, and digestibility was carried out inside metabolic cages. Dry matter and other nutrient intakes of lambs were not influenced by NPN source or the inclusion of tannin extract in the diet with the exception of the crude protein intake, which was higher (P\u202f≤\u202f0.05) in lambs receiving urea-containing diets. Tannin inclusion reduced (P