547
Effect of breed type and pasture type on methane emissions from weaned lambs offered fresh grasses
To investigate the extent to which enteric methane emissions from growing lambs are explained by simple body weight and diet characteristics, a 2 x 2 Latin square changeover design experiment was carried out using two sheep breed types and two fresh pasture types. Weaned lambs of two sheep breed types were used: Welsh Mountain (a small, hardy hill breed; mean LW = 27 ±3.6 kg) and Mule x Texel (prime lamb; 35 ±2.5 kg) (n = 8 per breed). The lambs were zero-grazed on material cut from contrasting high (ryegrass) and low (permanent pasture) digestibility pastures and fed fresh. In each experimental period, ad libitum DMI was determined individually indoors following an adaptation period of 2 wk, and methane emissions were measured individually in open-circuit respiration chambers over a period of 3 d. Mean pasture composition, as fed, for ryegrass and permanent pasture respectively, was: DM: 21.9 and 21.9 %; CP: 12.4 and 11.1 % DM; NDF: 41.2 and 53.3 % DM; GE: 17.3 and 17.1 MJ/kg DM. Although total daily methane emissions were lower for the Welsh Mountain lambs than for the Mule x Texel lambs (13 vs 16 g/d respectively; SED = 1.0; P < 0.05) when offered fresh forage, the yield of methane per unit DMI was similar for the two breed types (16.4 vs 17.7 g methane/kg DMI; SED = 0.79; NS). Total output of methane per day was higher when lambs were offered ryegrass compared to permanent pasture (16 vs 13 g/d respectively; SED = 0.49; P < 0.001) which was likely driven by differences in DMI (986 vs 732 g/d; SED = 22.4; P < 0.001). Methane emissions per unit DMI (16.4 vs 17.7 g methane/kg DMI; SED = 0.37; P < 0.01) and proportion of GE intake excreted as methane (4.9 vs 5.3 %; SED = 0.11; P < 0.01) were both higher on the permanent pasture. No forage x breed type interactions were identified. The results indicate that forage type had a greater impact than breed type on methane emissions from growing weaned lambs. It can be concluded that when calculating methane emissions for inventory purposes, it would be more important to know what feeds growing lambs are consuming than to know what breeds they are.
Keywords: lambs, grass, methane