Effects of dried distillers grains combined with low and high forage levels for dairy cows on productive performance

The objective of this study was to evaluate the interaction between dried distillers grains (DDG) inclusion and forage NDF (fNDF) concentration on nutrient intake, apparent partial and total-tract digestibility, feed sorting, milk yield (MY) and composition, nitrogen utilization, ruminal pH, and blood metabolites in lactating dairy cows. Twelve primiparous Holstein dairy cows, 6 of which were rumen-cannulated, with a mean (±SD) BW of 552 ± 27.9 kg, initial MY of 32.5 ± 1.36 kg/d, and DIM of 99 ± 24.5, were blocked by MY and DIM. They were randomly assigned to a replicated 6 × 6 incomplete Latin square design in a 3 × 2 factorial arrangement. Diets contained 0, 20, or 40% DDG (DM basis) combined with low fNDF (21%) or high fNDF (31%) levels. Significant DDG × fNDF interactions were observed for CP and NFC intake, NDF total-tract digestibility, ECM, 3.5% fat-corrected milk, feed efficiency, milk protein concentration, nonfat solids concentration, and nitrogen retention. At 21% fNDF, increasing DDG inclusion reduced CP and NFC intake, milk protein concentration, and nitrogen retention, whereas at 31% fNDF, increasing DDG inclusion reduced NDF total-tract digestibility, ECM, 3.5% fat-corrected milk, and feed efficiency. Inclusion of 40% DDG consistently reduced DM, OM, NDF, and uNDF intakes, as well as total-tract digestibility of DM, OM, and CP, regardless of fNDF levels. In contrast, inclusion of up to 20% DDG maintained intake, digestibility, and MY across fNDF levels. These results demonstrate that the negative effects of high DDG inclusion are exacerbated under high fNDF conditions, highlighting the importance of considering forage fiber concentration when formulating diets with DDG for lactating dairy cows.