SUMMARYThe current study evaluated the nutritional impact of crude glycerine (CG) supplementation to wethers fed only forage grass. Eight Polwarth wethers were used in a replicated 4 × 4 Latin Square. Treatments consisted of no CG (control, CON) or intra-ruminal infusion of CG at daily rates of 0·5, 1·5 or 3·0 ml/kg body weight (BW). In each Latin Square, four animals were fedAvena strigosaand four were fedCynodonsp. hayad libitum. The actual concentration of glycerol in diet was similar for both forage types and varied from 21 to 364 g/kg dry matter. No interactions between forage type and CG treatments were detected and no differences were observed between the CON and 0·5 CG treatment for most variables. Both the organic matter (OM) and the digestible OM intake decreased linearly at increased levels of CG infusion, whereas no treatment effect was observed on OM and neutral detergent fibre (NDF) digestibility. The duodenal flow of rumen microbial nitrogen (N) was not affected, whereas the duodenal flow of α-amino N decreased linearly at increased levels of CG infusion. In conclusion, CG supplementation at a rate of up to 0·5 ml/kg BW/day did not change the nutrient supply whereas greater amounts of CG supplementation negatively impacted the nutrient supply to wethers fed only grass forage. The forage digestibility, in turn, was not affected by CG supplementation.