Effect of dietary fat source and concentration on feed intake, enteric methane, and milk production in dairy cows

Dietary fat can be used in dairy cow nutrition to reduce enteric methane (CH₄), but studies with multiple dietary fat concentrations are scarce. Among fat sources, rapeseed is easily accessible in Europe and North America, and palm kernel fat has been shown to be a potent inhibitor of ruminal methanogenesis. Forty-eight cows (half primiparous and half multiparous) were used in a 6 × 6 Latin square design, with 6 periods of 21 d each. Six treatments were used: a control, 3 fat concentrations (low, medium, and high) of rapeseed (RS), and 2 fat concentrations (low and medium) of palm kernel fatty acids (PK). The total crude fat concentrations ranged from 3% to 7% of DM. The cows were fed the treatments as a partial mixed ration, and they received additional concentrate from the GreenFeed units (1 unit for 12 cows) used to measure CH₄ production. Increased dietary crude fat concentration of both RS and PK reduced DMI. The reduction in DMI was stronger in cows fed medium concentration of PK than for any RS concentration, which was comparable to previous studies for both RS and PK. Digestibility of OM was highest at low fat concentration of both fat sources, and lowest at high RS concentration. Digestibility of NDF was reduced by 2 percentage units when cows were fed medium PK concentration instead of the control treatment. Rapeseed supplementation with dietary crude fat up to 5.7% of DM increased milk and ECM yields, but the equivalent PK concentration reduced ECM. Increased fat supplementation decreased CH₄ yield (g CH₄/kg of DMI) linearly when RS was used, and quadratically when PK was used. The medium PK concentration reduced CH₄ yield more than medium RS concentration, but there was no difference for CH₄ intensity (g CH₄/kg of ECM). Rapeseed fat supplementation with dietary crude fat above 5.7% of DM could reduce further CH₄ yield, but fat supplementation was not accompanied by an increase in productivity. The fat source must be accounted for when considering enteric methane reduction, as the PK provided stronger effect than RS, but the associated reduction in milk production did not support the use of PK for methane reduction.