Effects of dietary concentrate supplementation on enteric methane emissions and performance of late lactation dairy cows

Dietary supplementation with concentrates is regarded as an effective strategy to decrease the intensity of methane (CH₄) emissions, although it has rarely been evaluated in late lactation dairy cows. The aim of the present study was to investigate the effects of two levels of dietary concentrate supplementation on CH₄ emissions and milk production and composition of dairy cows in late lactation. The study was conducted using 24 multiparous Holstein Friesian cows in late lactation (253 ± 18 d in milk), and had a duration of 3 wk, including 2 wk of adaptation to the diet and 1 wk of measurements. Treatments consisted of two levels of concentrate supplementation (4 vs. 8 kg d^-1 cow^-1; as-fed) offered daily in two equal rations during milking. In addition, diets included 2 kg DM grazed grass and 8 kg as-fed of grass hay. In week 3 of the study, CH₄ emissions were measured for 7 consecutive days using the sulfur hexafluoride tracer technique. Average total DM intakes for the cows fed the 4 and 8 kg concentrate treatments were 12.3 and 15.6 kg DM, respectively. Treatments had no effect on milk yield, milk fat, or milk lactose concentrations. Milk protein concentration tended to increase in cows offered 8 kg of concentrate. Higher concentrate intake tended to increase cow body mass gain, but not condition score change. The 8 kg treatment increased total CH₄ emissions (g d^-1) by 10.7%, whereas CH₄ yield (g kg^-1 DM intake) was decreased by 12.7%. Methane intensity (g kg^-1 milk yield) was unaffected by treatments. Dietary concentrate supplementation for late lactation cows is ineffective in mitigating CH₄ emission intensity, because animals do not respond with an increase in milk production.