| Forty Holstein cows averaging 78 d in milk were used in completely randomized design with a 2-wk covariate period followed by a 6-wk experimental period to evaluate incremental substitution of non-forage fiber provided by dried distillers grains with solubles (DDGS) and soyhulls (SH) for starch provided by corn in the diet. Four diets were formulated: (1) high starch (0% DDGS: 29% Starch), (2) medium starch (7% DDGS: 26% Starch), (3) low starch (14% DDGS: 23% Starch), and (4) very low starch (21% DDGS: 20% Starch). Diets contained 27% corn silage, 22% alfalfa hay, and 51% concentrate mix were formulated to be 17% CP, 4.7% fat, and 23% forage neutral detergent fiber (NDF). Total NDF increased as DDGS and SH were included in the diet. Soyhulls were included in a linear fashion along with DDGS to replace SBM and expeller soybean meal, thereby, to maintain similar CP level across the diets. As starch was replaced with non-forage fiber, DMI linearly decreased (P < 0.01). Average milk production during the study (38.2 kg/d) was not affected by diets. There were no treatment effects on milk fat and protein percentage nor milk fat and protein yield. Milk fatty acid profiles were similar across all diets. Other parameters including 4% fat-corrected milk (FCM), total solids (TS), and MUN were unaffected by dietary treatments. There was a tendency to linearly increase feed efficiency as starch was replaced by non-forage fiber (P < 0.07). Ruminal volatile fatty acid concentration (VFA) did not differ between diets. Concentration of blood metabolites, glucose and beta-hydroxybutyrate from coccegeal artery and mammary vein were similar across the diets. Results from this research suggest that non-forage fiber from DG can partially substitute for starch from corn in dairy cow diets without affecting milk production and milk composition. This indicates that DDGS can be used as an effective energy source to replace highly priced corn, hence decrease the feed cost associated with high corn diets.;Keywords: starch, corn, non-forage fiber, dried distillers grains with solubles. |
