Characterization of corn stover pelleted with soybean meal or dried distillers grains on lactating cow performance, eating behavior, and rumen function
The objective of this study was to determine the effects of alkali-treated corn stover pelleted with soybean meal (STV-SBM) or dried distillers grains (STV-DDG), on milk yield (MY), eating behavior and rumen fermentation in dairy cows. Fourty-five Holstein cows were used in replicated 5 × 5 Latin squares with 28-d periods, using a 2 × 2 + 1 augmented factorial arrangement of treatments. Diets were formulated to contain 10 or 15% corn stover-based pellets that replaced corresponding proportions of corn gluten feed pellets in the control diet. Treatments were: 1) Control (CON); 2) SBM10; 3) SBM15; 4) DDG10; and 5) DDG15. In each period, rumen pH was measured every 2 h for 24 h using 5 rumen-cannulated cows on d 21, and chewing behavior was visually recorded every 5 min for 24 h using 10 cows on d 27. Performance data were analyzed using the MIXED procedure of SAS and rumen data were analyzed as repeated measures. Overall, cows on CON diet had the greatest dry matter intake (DMI), 26.94 ± 0.49 kg/d, compared with 22.75 ± 0.49 kg/d for the average of the diets with experimental pellets. Cows on the CON diet produced 32.14 ± 0.70 kg milk/d whereas cows on the treatment diets produced 3.25 ± 0.70 less kg/d. Within diets containing pelleted stover, MY was greater in STV-SBM than STV-DDG by 0.45 ± 0.65 kg/d. Compared with CON, including 15% of either pelleted formulation increased milk production efficiency from 1.21 to 1.31. Concentration and yield of milk protein and lactose were decreased for all diets with pelleted stover relative to CON. For both pellet formulations, the inclusion level of 10% resulted in greater percentage and yield of fat, protein, and lactose than the 15% inclusion rate. Feeding STV-SBM resulted in greater milk fat concentration than CON and STV-DDG. Milk urea nitrogen tended to be lower in STV-DDG relative to STV-SBM. Cows fed the CON diet spent the least amount of time per kg of DMI compared with all other diets (8.0 vs. 10.76 ± 0.80 min/kg DMI). Cows consuming 15% spent more time eating compared with 10% inclusion level and displayed sorting behavior. Ruminating time was similar regardless of base and inclusion level. Despite differences in performance, mean rumen pH, ammonia concentration, total VFA concentration, acetate to propionate ratio, and rumen kinetics were similar among all diets. Dry matter and organic matter digestibility were decreased by corn stover-based pellets, except for DDG10; digestibility of crude protein was decreased in all treatments relative to CON and an interaction for fiber digestibility was observed where DDG10 had the greatest NDF and ADF digestibility. Nitrogen excretion via urine was reduced when cows consumed pelleted corn stover with DDGS whereas milk nitrogen was similar for both pellet formulations. Feeding corn stover pelleted with SBM or DDG affected cow eating behavior, which resulted in reduced milk yield associated with a decrease in DMI without negative effects on rumen health. Further refinement of pellet size, hardness, or inclusion level may be warranted to effectively incorporate pelleted corn stover in dairy rations.