Effects of a perennial ryegrass diet or total mixed ration diet offered to spring-calving Holstein-Friesian dairy cows on methane emissions, dry matter intake, and milk production

The objective of the present study was to compare the enteric methane (CH₄) emissions and milk production of spring-calving Holstein-Friesian cows offered either a grazed perennial ryegrass diet or a total mixed ration (TMR) diet for 10 wk in early lactation. Forty-eight spring-calving Holstein-Friesian dairy cows were randomly assigned to 1 of 2 nutritional treatments for 10 wk: 1) grass or 2) TMR. The grass group received an allocation of 17kg of dry matter (DM) of grass per cow per day with a pre-grazing herbage mass of 1,492kg of DM/ha. The TMR offered per cow per day was composed of maize silage (7.5kg of DM), concentrate blend (8.6kg of DM), grass silage (3.5kg of DM), molasses (0.7kg of DM), and straw (0.5kg of DM). Daily CH₄ emissions were determined via the emissions from ruminants using a calibrated tracer technique for 5 consecutive days during wk 4 and 10 of the study. Simultaneously, herbage dry matter intake (DMI) for the grass group was estimated using the n-alkane technique, whereas DMI for the TMR group was recorded using the Griffith Elder feeding system. Cows offered TMR had higher milk yield (29.5 vs. 21.1kg/d), solids-corrected milk yield (27.7 vs. 20.1kg/d), fat and protein (FP) yield (2.09 vs. 1.54kg/d), bodyweight change (0.54kg of gain/d vs. 0.37kg of loss/d), and body condition score change (0.36 unit gain vs. 0.33 unit loss) than did the grass group over the course of the 10-wk study. Methane emissions were higher for the TMR group than the grass group (397 vs. 251 g/cow per day). The TMR group also emitted more CH₄ per kg of FP (200 vs. 174g/kg of FP) than did the grass group. They also emitted more CH₄ per kg of DMI (20.28 vs. 18.06g/kg of DMI) than did the grass group. In this study, spring-calving cows, consuming a high quality perennial ryegrass diet in the spring, produced less enteric CH₄ emissions per cow, per unit of intake, and per unit of FP than did cows offered a standard TMR diet.