Effects of feeding beets and ensiled beets on postabsorptive ethanol metabolism and enteric gas emission in dairy cows

Beets have a high sugar content, which is primarily fermented to ethanol during ensiling. This study investigated the effects of feeding diets with sugar-rich beets or ethanol-rich beet silage to lactating dairy cows on postabsorptive ethanol metabolism, enteric gas emissions, and microbial protein synthesis. Beets were washed, crushed, and stored in daily portions either as is (frozen at -20°C for preservation) or ensiled in barrels. Four rumen-cannulated Danish Holstein cows were used in a replicated (one complete and one incomplete) 3 × 3 Latin square design, with 3 treatments and three 21-d periods. The control diet (CON) consisted of grass-clover silage, corn silage, barley, soybean meal, dried beet pulp, urea, and minerals. In the sugar-rich (SUG) and ethanol-rich (ETH) treatment diets, 20% of DM from CON was replaced with either beets or ensiled beets, respectively. To assess whole-body irreversible loss rate (ILR) and mammary extraction of ethanol and acetate, bilateral jugular catheters were placed for infusion of either [¹³C]-labeled ethanol or acetate, or blood sampling. Additionally, mammary venous blood was sampled by venipuncture. The DMI, milk yield, ethanol content in milk, methane emission, and nitrous oxide content in ruminal headspace gas were unaffected by diet. Plasma flow and mammary net uptake of metabolites, including acetate, ethanol, and amino acids, were also unaffected by diet. Furthermore, feeding 350 g/d of ethanol did not alter the whole-body ILR of ethanol or acetate. The mammary glands were responsible for 57% of the whole-body ILR of ethanol, with a negligible portion secreted into milk. For acetate, the mammary glands were responsible for 39% of the whole-body ILR. In conclusion, feeding 0.35 kg/d of ethanol did not affect the net uptake of ethanol or acetate by the mammary gland or excretion of ethanol in milk. Additionally, feeding either form of beets increased hydrogen emissions but there were no differences in methane emissions among diets.