Effect of substituting maize silage with fresh or ensiled sugar beets on nutrient digestibility, rumen fermentation and microbial synthesis, and enteric methane emission in dairy cows

Abstract

This study aimed to 1) examine nutrient digestibility, rumen fermentation and microbial synthesis, and enteric methane emission when feeding diets high in sugar content provided as freshly stored or ensiled sugar beets to dairy cows, and 2) to evaluate the methane mitigation potential of ensiled sugar beets with different nutrient composition (sugar vs. alcohol) by use of an additive during ensiling. Four rumen, duodenal and ileal fistulated Danish Holstein dairy cows were used in a 4 × 4 Latin square design with 21-d periods. Maize silage was included in the control diet (CON) and was partially replaced in the experimental diets with either freshly stored sugar beets (SBF), ensiled beets with ensiling additive (SBE+), or ensiled beets without ensiling additive (SBE−) at 196 g/kg dietary dry matter (DM) content. Cows adapted to the diets for 11 d, after which rumen liquid and digesta were collected over 5 d, and gas exchange was measured in respiration chambers over the next 5 d. Dry matter intake (DMI), daily methane production, and methane per kg organic matter (OM) intake, rumen digested OM, and energy-corrected milk (ECM) yield were unaffected by diet. Methane per kg DMI (tendency) and per kg OM intake was lower for SBE– compared to SBF. Nutrient digestibility of DM, OM, starch, and neutral detergent fibre in different sections of the digestive tract were unaffected by diet. Molar proportion of acetate in rumen liquid decreased for ensiled sugar beet diets relative to CON, while molar proportions of propionate and acetate-to-propionate ratio remained unaffected. Molar proportion of butyrate was higher for SBE+ than CON. Microbial crude protein synthesis and microbial efficiency were unaffected by diet. Milk yield and ECM yield (tendency) were lower for SBE+ than CON. In conclusion, freshly stored sugar beets and sugar beets ensiled with or without additive, can replace maize silage in dairy cattle rations without adverse effects on DMI, rumen fermentation, and nutrient digestibility, and without altering most expressions of methane emissions, but methane per kg of OM intake was lower for beets ensiled without additive compared to freshly stored beets. The ECM yield, however, tends to be lowered for ensiled beets with additive.