Effects of dietary glycerol monolaurate supplementation on milk production and methane emissions in Holstein dairy cows

Glycerol monolaurate (GML) has antimicrobial and anti-inflammatory properties in non-ruminants. In vitro, GML reduces methane (CH 4 ) production; however, the effects of dietary GML supplementation on milk production and CH 4 emissions have not been evaluated in dairy cattle. In a completely randomized design, 42 mid-lactation Holstein cows (3.10 ± 1.08 lactations; 40.0 ± 6.65 kg milk/day) were acclimated to a tie-stall barn for 3 weeks and assigned to 1 of 3 treatments (n = 14/treatment): unsupplemented (CON), low dose GML (50 g/day; LD), or high dose GML (150 g/day; HD) for a 21-d experimental period. Cows were fed a base diet composed of corn silage, grass haylage, and concentrates and milked thrice daily. During the final week of acclimation and the experimental period, milk was sampled consecutively for 9 milkings/week. Methane, carbon dioxide (CO 2 ), and hydrogen (H 2 ) gas measurements were collected 3 times per day over 4 d (12 samples/cow) using the GreenFeed system (C-Lock, Inc., Rapid City, SD). The statistical model included fixed effects of treatment, day, and treatment × day as well as random effect of cow. Planned contrasts to compare CON vs. LD and CON vs. HD were employed. Dry matter intakes (DMI), milk yields, and energy-corrected milk (ECM) yields were not affected by treatment. However, HD cows tended to produce more 3.5% fat-corrected milk (FCM), relative to CON (46.6 vs. 44.8 kg/day; P = 0.13). Milk fat contents (4.22 vs. 4.01%) and yields (1.76 vs. 1.62 kg/day) were greater in HD, relative to CON ( P = 0.05). The LD and HD cows had higher contents and yields of de novo fatty acids, including lauric acid, relative to CON ( P = 0.01). Milk protein contents were lower for HD cows, relative to CON (3.42 vs 3.49%; P = 0.01). Milk protein yields were lower in LD and HD, relative to CON (1.46, 1.46, and 1.52 kg/day, respectively; P ≤ 0.05). Milk lactose contents and yields were not affected by treatment. Cows provided the HD treatment tended to have improved feed efficiency (i.e., kg of milk, 3.5% FCM, and ECM per unit of dry matter intake), relative to CON ( P = 0.13). Methane production, intensity, and yield, and CO 2 and H 2 production were not affected. We conclude that dietary GML supplementation altered milk production; however, GML feeding at the levels used in this study did not modify enteric CH 4 production, intensity, or yield in dairy cattle.