Abstract
To investigate the extent to which enteric methane (CH4) emissions from growing lambs are explained by simple body weight and diet characteristics, a 2 × 2 Latin square changeover design experiment was carried out using two sheep breeds and two fresh pasture types. Weaned lambs of two contrasting breed types were used: Welsh Mountain (WM, a small, hardy hill breed) and Welsh Mule × Texel (TexX, prime lamb) (n = 8 per breed). The lambs were zero-grazed on material cut from recently reseeded perennial ryegrass and extensively managed permanent pasture. In each experimental period, individual ad libitum dry matter intake (DMI) was determined indoors following an adaptation period of 2 weeks, and CH4 emissions were measured individually in open-circuit respiration chambers over a period of 3 days. Although total daily CH4 emissions were lower for the WM lambs than for the TexX lambs (13·3 v. 15·7 g/day, respectively) when offered fresh forage, the yield of CH4 per unit DMI was similar for the two breed types (16·4 v. 17·7 g CH4/kg DMI). Total output of CH4 per day was higher when lambs were offered ryegrass compared with permanent pasture (16·1 v. 12·9 g/day, respectively), which was probably driven by differences in DMI (986 v. 732 g/day). Methane emissions per unit DMI (16·4 v. 17·7 g CH4/kg DMI) and proportion of gross energy intake excreted as CH4 (0·052 v. 0·056 MJ/MJ) were both higher on the permanent pasture. No forage × breed type interactions were identified. The results indicate that forage type had a greater impact than breed type on CH4 emissions from growing weaned lambs. It can be concluded that when calculating CH4 emissions for inventory purposes, it is more important to know what forages growing lambs are consuming than to know what breeds they are.
Highlights
The livestock sector faces major challenges in reducing its contribution to global environmental problems (Steinfeld et al 2006)
For the first time, CH4 emissions from growing weaned lambs fed on pastures representative of those used in UK sheep production systems
Data were collected for weaned lambs offered material from swards representative of the pastures used by commercial producers at the corresponding stage of the sheep production cycle
Summary
The livestock sector faces major challenges in reducing its contribution to global environmental problems (Steinfeld et al 2006). As part of a multi-centre research programme developing revised EFs for sheep and cattle the current experiment investigated the extent to which breed × diet relationships for growing lambs were explained solely by simple body weight and digestibility characteristics of the animal and diet, respectively, with no interactions. It quantified, for the first time, CH4 emissions from growing weaned lambs fed on pastures representative of those used in UK sheep production systems
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