Ruminal fermentation, kinetics, and total-tract digestibility of lactating dairy cows fed distillers dried grains with solubles in low- and high-forage diets

摘要

The objective of this study was to investigate theeffects of concentrations of forages and corn distillersdried grains with solubles (DDGS) on ruminal fermentation,ruminal kinetics, and total-tract digestibility ofnutrients in lactating dairy cows. Four lactating Holsteincows with ruminal cannulas were assigned to a4 × 4 Latin square in a 2 × 2 factorial arrangementof treatments. Diets were formulated to contain lowforage [LF; 17% forage neutral detergent fiber (NDF)]or high forage (HF; 24.5% forage NDF) and DDGS at0 or 18% (0DG or 18DG) of diet dry matter (DM).Intake of DM was not affected by the diets. Daily meanruminal pH was affected by forage NDF × DDGS interactions,as the lowest ruminal pH was observed amongcows fed LF18DG (6.02). Apparent total-tract digestibilityfor DM, organic matter, crude protein, NDF,acid detergent fiber, and starch was not affected bydiets. Cows fed LF diets had a greater total volatilefatty acid concentration compared with cows fed HF(122 vs. 116 mM). Molar proportions of acetate weregreater for HF compared with that of LF diets (62.6 vs.57.5 mmol/100 mmol) and greater for 0DG diet comparedwith that of 18DG diets (61.3 vs. 58.7 mmol/100mmol) diets. The molar proportion of propionate wasaffected by forage × DDGS interaction as the greatestpropionate molar proportion was observed with cowsfed LF18DG diet (27.7 mmol/100 mmol). Also, molarproportion of butyrate was affected by forage × DDGSinteraction, as the greatest butyrate molar proportionwas observed in cows fed HF18DG diet (13.5 mmol/100mmol). Average fractional dilution rate for all diets was11.9%/h and was not affected by diets. Fractional passagerate of the solid phase was greater for HF thanfor LF (4.40 vs. 3.76%/h). The ruminal retention timeof solid phase was greater for LF compared with HFdiets (27.3 vs. 23.3 h). Fractional passage rate of DDGSwas affected by forage × DG interaction, as the highestfractional passage rate of DDGS was observed withcows fed HF18DG diet (7.72%/h). Our results demonstratedthat concentrations of forage, DDGS, and theirinteraction influence ruminal degradation and kineticsof diets fed. Diets formulated at 17% forage NDF at17% (DM basis) can decrease milk fat concentrationcompared with diets formulated at 25% forage NDF.Additionally, feeding DDGS at 18% DM basis to lactatingdairy cows did not affect milk fat concentration oryield.