Effects of feeding fresh white clover (Trifolium repens) or perennial ryegrass (Lolium perenne) on enteric methane emissions from sheep

Enteric CH4 contributes about one third of New Zealand's greenhouse gas emissions. Measurements from our laboratory using the sulfur hexafluoride (SF6) technique suggested much lower CH4 yields (as gCH4/kg dry matter (DM) intake) from sheep fed fresh white clover (Trifolium repens) compared with fresh perennial ryegrass (Lolium perenne). Thus, white clover offers an opportunity to reduce CH4 emissions from pastoral based ruminant livestock systems if its lower CH4 yield can be confirmed using respiration chambers. This study was comprised of 2 experiments where good nutritional quality freshly harvested white clover and perennial ryegrass were fed to 16 sheep in Experiment 1 (8/diet) and 32 sheep in Experiment 2 (16/diet). Intakes were about 1.6 times metabolizable energy requirements for maintenance (×MEm) in Experiment 1 and 0.8×MEm and 2.0×MEm in Experiment 2 (8/diet/feeding level). In both experiments sheep had a 10 d acclimatization to their diets and CH4 emissions were measured in respiration chambers for 2 consecutive days. Methane yield (gCH4/kg DM intake) was 12% lower (P=0.04) for white clover (19.8) compared with ryegrass fed sheep (22.5) in Experiment 1. In Experiment 2, there were no effects of forage on CH4 yield (as gCH4/kg DM intake) at 0.8×MEm (27.1 and 25.5, respectively) but, at 2.0×MEm, CH4 yield (as gCH4/kg DM intake) was 7% higher (P=0.05) for white clover (23.4) compared with ryegrass (21.7). Analyses of combined data from both experiments show that there were no overall dietary effects on CH4 yield, but increased intakes reduced CH4 yield (P<0.01). Use of white clover as an alternative fresh forage to ryegrass is not an opportunity to reduce enteric CH4 emissions from sheep.