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

Authors: RANATHUNGA, SANJEEWA - South Dakota State University; Kalscheur, Kenneth; HERRICK, KEVIN - South Dakota State University

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2019
Publication Date: 9/1/2019
Citation: Ranathunga, S.D., Kalscheur, K., Herrick, K.J. 2019. Ruminal fermentation, kinetics, and total-tract digestibility of lactating dairy cows fed distillers dried grains with solubles in low-and high-forage diets. Journal of Dairy Science. 102(9):7980–7996. https://doi.org/10.3168/jds.2018-15771.
DOI: https://doi.org/10.3168/jds.2018-15771

Interpretive Summary: Incorporation of distillers dried grains with solubles (DDGS) in lactating dairy cow diets has become a common feeding practice in the United States. It can be used as an alternative protein supplement to soybean meal or as alternative energy source to corn because of its undegradable protein, digestible fiber, and fat concentration. The major concern with feeding a greater amount of DDGS is that there is a possibility of causing decreased milk fat concentration. While no single factor may be responsible for decreased milk fat conentration, interactions of several dietary factors including greater amounts of digestible carbohydrates, inadequate effective fiber, and a greater concentration of polyunsaturated fatty acids could lead to milk fat reduction. The objective of this study was to investigate the effect of no DDGS or the addition of 18% DDGS into diets formulated with low or high forage concentrations on ruminal fermentation and total tract digestibility of lactating dairy cows. Results demonstrated that concentrations of forage and the inclusion of DDGS influence ruminal degradation and total tract digestibility. This study demonstrates to dairy producers and nutritionists that providing an adequate amount of forage fiber is essential when feeding DDGS at greater concentrations in order to prevent altered ruminal fermentation and incomplete conversion of unsaturated fatty acids to saturated fatty acids resulting in a lower milk fat concentration.

Technical Abstract: The study objective was to investigate the effects of concentrations of forages and corn distillers dried grains with solubles (DDGS) on ruminal fermentation, ruminal kinetics and total tract digestibility of nutrients in lactating dairy cows. Four lactating Holstein cows with ruminal cannulas were assigned to a 4 × 4 Latin square in a 2 × 2 factorial arrangement of treatments. Diets were formulated to contain low forage [LF; 17% forage neutral detergent fiber (NDF)] or high forage (HF; 24.5% forage NDF) and DDGS at 0 or 18% (0DG or 18DG) of diet DM. Dry matter intake was not affected by the diets. Daily mean ruminal pH was affected by forage NDF × DDGS interactions as the lowest ruminal pH was observed with cows fed LF18DG (6.02). Apparent total tract digestibility for DM, OM, CP, NDF, ADF, and starch was not affected by diets. Cows fed LF diets had a greater total VFA concentration compared with cows fed HF (122 vs. 116 mM). Molar proportions of acetate were greater for HF compared to that of LF diets (62.6 vs. 57.5 mmol/100 mmol) whereas it was greater for 0DG diet compared to that of 18DG diets (61.3 vs. 58.7 mmol/100 mmol) diets. The molar proportion of propionate was affected by forage × DDGS interaction as the greatest propionate molar proportion was observed with cows fed LF18DG diet (27.7 mmol/100 mmol). Also, molar proportion of butyrate was affected by forage × DDGS interaction as the greatest butyrate molar proportion was observed with cows fed HF18DG diet (13.5 mmol/100 mmol). Average fractional dilution rate for all diets was 11.9%/h and was not affected by diets. Fractional passage rate of the solid phase was greater for HF compared with LF (4.40 vs. 3.76%/h). The ruminal retention time of solid phase was greater for LF compared with HF diets (27.3 vs. 23.3 h). Fractional passage rate of DDGS was affected by forage × DG interaction as the highest fractional passage rate of DDGS was observed with cows fed HF18DG diet (7.72%/h). Our results demonstrated that concentrations of forage, DDGS and their interaction influence ruminal degradation and kinetics of diets fed. Diets formulated at 17% forage NDF at 17% (DM basis) can decrease milk fat concentration compared to diets formulated at 25% forage NDF. Additionally, feeding DDGS at 18% DM basis to lactating dairy cows did not affect milk fat concentration or yield.