Effects of concentrate main carbohydrate type on methane emissions, milk production and feeding behavior in grazing late-lactation dairy cows.

Dairy production in temperate regions relies on herbage as the main source of feed and supplements are fed to cope with a decrease in herbage quality and quantity during summer. The objective of the current study was to evaluate the effect of no supplementation or supplementation with high-starch, high-fiber, or mixed concentrates (50 starch:50 fiber) in grazing late lactation dairy cows on methane (CH4) emissions, milk production and feeding behavior. Seventy-two multiparous lactating dairy cows (Holstein-Friesian × Jersey; 206 ± 9.5 days in milk) were assigned to receive 0 kg/d of concentrate (CTR) or 5 kg/d of high starch (STA), high fiber (FIB) or a 50:50 mix of STA and FIB concentrate (MIX) during milking. Methane production was measured using two GreenFeed units for 36 days, with 60 cows having sufficient visits to be included in the data analysis. Feeding behavior was recorded using Nedap CowControl™ collars. Milk production was recorded daily, and milk composition was determined weekly. The daily CH4 production was similar among dietary treatments. The fat and protein-corrected milk production (FPCM) was 16% greater in MIX and STA compared to CTR cows (P < 0.01), with FIB cows intermediate. Methane as g/kg FPCM was 14 and 13% less (P = 0.02) in MIX and STA compared to CTR-fed cows, with FIB cows intermediate. Eating rate and rumination rate (min/kg of dry matter intake) were positively correlated with CH4 expressed as g/kg FPCM and as g/kg of total solids (r = 0.30 to 0.44). In conclusion, supplementing grazing late lactation dairy cows in summer with concentrates can be a strategy to increase FPCM and reduce the CH4/FPCM.