Methane emissions by dairy cows fed increasing proportions of white clover (Trifolium repens) in pasture

Abstract

Methane (CH4) production from ruminant digestion has a significant impact on the New Zealand greenhouse gas (GHG) inventory and represents a loss of about 10% of metabolisable energy (ME) intake. Previous trials with sheep and cattle have demonstrated significantly lower methane losses per unit feed intake from legumes compared to grass dominant pasture. Most trials have compared forages fed as sole diets but white clover (Trifolium repens) is usually fed with perennial ryegrass (Lolium perenne) as a mixed pasture, as it complements ryegrass for animal production. An indoor feeding trial was conducted in December 2003 with thirty-two Holstein-Friesian dairy cows in mid-lactation to determine effects of increasing proportions of white clover on methane emissions and cow performance. Cows were housed indoors and fed perennial ryegrass with 0, 15, 30 or 60% white clover ad libitum on a dry matter (DM) basis. Increasing proportions of white clover resulted in linear increases in dry matter intakes (DMI) and reductions in methane per kg DM eaten, although the extent to which CH4 production/kg DMI was lowered was less than anticipated from previous measurements from sheep fed white clover as a sole diet. DMI of cows fed 60% white clover was 20.5 vs. 15.6 kg DM/cow/day for 100% perennial ryegrass (P<0.001) with 18.1 vs. 21.7 g CH4/kg DM for the respective treatments. The increased DMI of cows fed increased levels of white clover resulted in a significant but small increase in total daily CH4 emissions. Milk and milksolids yields also increased from 17.6 to 20.4 kg/ cow/day (P<0.001) and 1.32 to 1.52 kg/cow/day (P<0.005) respectively as the proportion of white clover increased from 0 to 60%. Keywords: dairy cow, methane emissions, milk production, perennial ryegrass, white clover