In recent years, members of the public, government, and industry have voiced concerns about the environmental impact of dairy production, especially regarding methane emissions. As both milk demand and global temperatures continue to rise, it is becoming increasingly important to investigate strategies for reducing methane emissions from lactating dairy cows. Two studies were conducted to examine the effects of various feeding strategies on enteric methane emissions in mid-lactation dairy cows. For Experiment 1, I investigated the effects of dietary supplementation of the monoglyceride glycerol monolaurate (GML) on milk production and methane emissions. Glycerol monolaurate has antimicrobial and anti-inflammatory properties in non-ruminants. Previous research has demonstrated that GML reduces methane production in rumen fluid; however, the effects of dietary GML supplementation on milk production and enteric methane emissions had not been evaluated in dairy cattle. In a completely randomized design, 42 mid-lactation Holstein cows (3.10 ± 1.08 lactations; 116 ± 34.9 days in milk; 40.0 ± 6.65 kg milk/day) were acclimated to a tie-stall barn 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-day experimental period. Dry matter intakes, milk yields, and energy-corrected milk (ECM) yields were not modified by treatment. However, HD cows tended to produce more 3.5% fat-corrected milk, and have greater milk fat contents and yields, relative to CON. The LD and HD cows had higher contents and yields of de novo fatty acids (FA), including lauric acid, relative to CON. Milk protein contents were lower for HD cows and milk protein yields were lower in both LD and HD, relative to CON. Cows provided the HD treatment tended to have improved feed efficiency relative to CON. Methane production, intensity, and yield, and carbon dioxide and hydrogen production were not modified. I conclude that dietary GML supplementation increased milk fat production; however, short-term GML feeding did not modify enteric methane production, intensity, or yield in dairy cattle. For Experiment 2, I investigated the effects of dietary starch concentration on milk production, nutrient digestibility, and methane emissions. Starch fermentation promotes the production of propionate at the expense of acetate and lowers rumen pH, making the rumen environment less favorable to methanogens. Thirty mid-lactation Holstein cows (2.53 ± 1.78 lactations; 117 ± 24.9 days in milk; 38.3 ± 9.13 kg milk/day) were enrolled in a study with completely randomized design. After acclimation, cows were assigned to 1 of 2 treatments (n = 15/group): a high neutral detergent fiber (aNDFom) and low starch diet (LS) or a low aNDFom and high starch diet (HS) for an 8-week experimental period. Dry matter intakes and milk yields were greater in HS cows, relative to LS cows, though HS cows had a decreased feed efficiency. The ECM yields, protein contents, protein yields, and lactose yields were greater for HS cows. Apparent total-tract dry matter and organic matter digestibilities were greater for HS cows. Plasma insulin concentrations tended to be greater in HS cows. Dietary starch content altered milk FA profile, with the LS cows having greater mixed FA contents and the HS cows having greater de novo FA contents and yields. Methane production tended to be higher for HS cows, but methane yields were significantly lower for HS cows. Methane production was negatively correlated with anteiso C15:0, C16:1 trans-9, C18:1 cis-9, and C20:1 cis-11. I conclude that a HS diet improves milk production, digestibility of DM and OM, and reduces methane yield in dairy cattle; however, increased ECM did not correspond to reduced methane intensity.