Oats in the diet of dairy cows: milk production and enteric methane emissions

The overall aim of this thesis was to investigate whether replacing barley with oats as a grain supplement for dairy cows could reduce enteric methane (CH4) emissions without compromising milk production. Barley is a more common grain supplement in Sweden, mainly due to higher tabulated feeding values suggesting higher milk production with barley than with oats. In the first paper, different varieties of oats and barley were evaluated in vitro. Predicted in vivo CH4 emissions were lower from the oat diets than from the barley diets. In the second paper, barley was replaced by hulled oats as a grain supplement to dairy cows fed a grass silage-based diet. Replacing barley with oats decreased organic matter digestibility and metabolisable energy intake but did not affect milk or energy-corrected milk (ECM) yield. Daily CH4 emissions (g/d) and CH4 intensity (g/kg ECM) decreased by 4.7 and 4.8%, respectively. In the third paper, dairy cows were fed one of four grain supplements: barley, hulled oats, dehulled oats, or a mix of hulled and dehulled oats. Organic matter digestibility and metabolisable energy intake were similar between the barley diet and the oat diets, but milk and ECM yield were higher with the oat diets. Replacing hulled oats with dehulled oats did not affect milk or ECM yield. Daily CH4 emissions were similar between the barley diet and the oat diets. Yet, due to higher ECM yield, CH4 intensity was 5.7% lower with the oat diets. In the fourth paper, we investigated fatty acid composition of milk. Milk fat from cows fed oats contained lower concentrations of saturated fatty acids and higher concentrations of unsaturated fatty acids. In conclusion, replacing barley with oats in the diet of dairy cows does not compromise milk production and could offer a practical strategy to slightly reduce enteric CH4 emissions and to change milk quality to be more in line with dietary guidelines.