The replacement of maize silage by urea-treated whole-crop barley in the diets of Iranian native sheep

The replacement value of urea-treated whole-crop barley (UWB) for maize silage given to sheep was investigated in this study. A completely randomized design of four treatments using 32 Iranian native sheep (n = 8 per treatment) was used to investigate the potential replacement of maize silage with urea-treated whole-crop barley (var. Herta). The four dietary treatments were ad libitum maize silage alone (A) or mixed with UWB at the ratios of 65:35 (B), 50:50 (C) and 35:65 (D) on DM basis. Each diet was supplemented with 200 g DM/day of concentrate (143 g CP/kg DM; 11.2 MJ/kg DM). The progressive decline in forage DM intakes with increasing proportion of UWB in the diet (1.14, 0.99, 1.01 and 0.85 kg/day for treatments A–D, respectively; P < 0.05) led to reductions in live-weight gain (109, 109, 123 and 92 g/day for treatments A–D, respectively; P < 0.05); feed conversion ratio (12.2, 11.0, 9.1 and 9.6 kg DM intake/kg gain for treatments A–D, respectively) and increases in feed efficiency ratio (9.6, 11.0, 12.2 and 10.8 kg gain/100 kg total DM intake for treatments A–D, respectively; P < 0.05). The concentrations of urea in blood serum increased significantly with the increasing proportions of UWB and were at their maxima 4 h after feeding, for A–D, respectively, 4.02, 6.52, 8.12 and 9.01 mmol/l (P < 0.01). No significant changes in serum protein fractions, calcium or phosphorus were observed between treatments. Urea-treated whole-crop barley can replace up to 50% of maize silage in the ration of Iranian native sheep without potentially affecting animal performance and meat production.