Effect of forage level and replacing canola meal with dry distillers grains with solubles in precision-fed heifer diets: Digestibility and rumen fermentation.

Objectives of this study were to determine the effects of feeding differing forage-to-concentrate ratios (F:C) and inclusion rates of corn dry distillers grain with solubles (DDGS) on digestion and rumen fermentation in precision-fed dairy heifer rations. A split-plot design with F:C as whole plot and DDGS inclusion level as sub-plot was administered in a 4-period (19 d) 4 × 4 Latin square. Eight rumen-cannulated Holstein heifers (12.5 ± 0.5 mo of age and 344 ± 15 kg of body weight) housed in individual stalls were allocated to 2 F:C [50:50, low forage, or 75:25 high forage; dry matter (DM) basis] and to a sequence of DDGS inclusion (0, 7, 14, and 21%; DM basis). Forage was a mix of 50% corn silage and 50% grass hay (DM basis). Diets were fed to allow for 800 g/d of body weight gain and fed 1×/d. Rumen contents were sampled at -2, 0, 2, 4, 6, 8, 10, 12, and 20 h after feeding for rumen fermentation measures. Low-forage rations had greater DM and organic matter apparent digestibility. We detected a quadratic effect for DM, organic matter, acid detergent fiber, and neutral detergent fiber apparent digestibility, with the 14% DDGS inclusion level having the highest values. Nitrogen retention decreased with increasing levels of DDGS. Molar proportions of acetate tended to be greater for HF and decreased as DDGS increased; propionate increased as DDGS increased, resulting in the opposite effect on acetate to propionate ratio. Rumen protozoa count decreased as DDGS increased. Moderate levels (14% of DM) of DDGS appear to enhance nutrient utilization and fermentation in precision-fed dairy heifers fed different F:C diets.