Effect of concentrate feed level on methane emissions from grazing dairy cows

摘要

Although the effect of nutrition on enteric methane , (CH_4) emissions from confined dairy cattle has been extensively examined, less information is available on factors influencing CH_4 emissions from grazing dairy cattle. In the present experiment, 40 Holstein-Friesian dairy cows (12 primiparous and 28 multiparous) were used to examine the effect of concentrate feed level (2.0, 4.0, 6.0, and 8.0 kg/cow per day; fresh basis) on enteric CH_4 emissions from cows grazing perennial ryegrass-based swards (10 cows per treatment). Methane emissions were measured on 4 occasions during the grazing period (one 4-d measurement period and three 5-d measurement periods) using the sulfur hexafluoride technique. Milk yield, liveweight, and milk composition for each cow was recorded daily during each CH_4 measurement period, whereas daily herbage dry matter intake (DMI) was estimated for each cow from performance data, using the back-calculation approach. Total DMI, milk yield, and energy-corrected milk (ECM) yield increased with increasing concentrate feed level. Within each of the 4 measurement periods, daily CH_4 production (g/d) was unaffected by concentrate level, whereas CH_4/DMI decreased with increasing concentrate feed level in period 4, and CH_4/ECM yield decreased with increasing concentrate feed level in periods 2 and 4. When emissions data were combined across all 4 measurement periods, concentrate feed level (2.0, 4.0, 6.0, and 8.0 kg/d; fresh basis) had no effect on daily CH_4 emissions (287, 273, 272, and 277 g/d, respectively), whereas CH_4/DMI (20.0, 19.3, 17.7, and 18.1 g/kg, respectively) and CH_4-E/gross energy intake (0.059, 0.057, 0.053, and 0.054, respectively) decreased with increasing concentrate feed levels. A range of prediction equations for CH_4 emissions were developed using live-weight, DMI, ECM yield, and energy intake, with the strongest relationship found between ECM yield and CH_4/ECM yield (coefficient of determination = 0.50). These results demonstrate that offering concentrates to grazing dairy cows increased milk production per cow and decreased CH_4 emissions per unit of milk produced.