Enteric methane emission and digestion in dairy cows fed wheat or molasses

摘要

The aim of this experiment was to measure entericmethane (CH_4) emission and its relation with rumendigestion in dairy cows fed diets rich in 1 of the 2 carbohydratesources, starch or sugar. The rations werebased on late first-cut grass–clover silage supplementedwith wheat (Wh), NaOH-treated wheat (Wh+NaOH),sugar beet molasses (Mo), or sugar beet molasses withaddition of sodium bicarbonate (Mo+Bic). Wheat andmolasses made up 35% of dry matter in the 2 dietswith molasses and wheat, respectively. Four cows fittedwith ruminal, duodenal, and ileal canulae were used ina 4 × 4 Latin square design. Nutrient digestibility wasmeasured using chromium oxide and titanium oxideas flow markers, and emissions of CH_4 and hydrogenwere measured via open-circuit indirect calorimetry on4 consecutive days. Data were analyzed using PROCMIXED of SAS (version 9.4; SAS Institute Inc., Cary,NC) with treatment and period as fixed effects and cowas random effect. Furthermore, orthogonal contrastswere calculated. The cows produced 32.5, 33.6, 36.2,and 35.1 L of CH_4/kg of dry matter intake (DMI) ondiets Wh, Wh+NaOH, Mo, and Mo+Bic, respectively.The emission of CH_4 per day, per kilogram of DMI, andper kilogram of energy-corrected milk as well as dailyhydrogen emission were higher on the Mo diet comparedwith the Wh diet. With the present inclusion of wheatand molasses in the diet, no effects of NaOH treatmentof wheat or of sodium bicarbonate supplementationto the Mo diet could be demonstrated on CH_4 emissionexpressed per kilogram of DMI or per kilogramof energy-corrected milk. The duodenal flow of starchwas higher when wheat was treated with NaOH. Underthe conditions in the present experiment, ruminal NDFdigestibility was not affected by carbohydrate source,NaOH treatment of wheat, or bicarbonate supplementation.Total volatile fatty acid concentration in the rumenand the proportions of acetate and propionate werenot affected by carbohydrate source, NaOH treatmentof wheat, or bicarbonate supplementation. Likewise,we could not show any influence of diet on microbialprotein synthesis or efficiency of microbial protein synthesisexpressed as grams of microbial protein synthesisper kilogram of true rumen-digested organic matter.We concluded that CH_4 emission was increased whenwheat was replaced by molasses, whereas no effect ofmanipulating rumen fermentation by NaOH treatmentof wheat or addition of bicarbonate to molasses couldbe found with a level of approximately 25% of dry matterfrom starch and sugar, respectively.