All three diets contained similar crude protein (16.5 percent) and protein fractions, fat (3.9 percent) and sugar (6.8 percent). Ration NDF was lower for the standard diet (34.7 percent) than either the higher- forage or non-forage fiber source diets which were similar (38.1 percent). The peNDF content of the standard diet was also lower (18.5 percent) than the higher-forage diet (25.9 percent) simply reflecting the differences in forage content, and the non-forage fiber source diet was intermediate at 22 percent. Starch content was greatest for the standard diet (26.0 percent) and lower for the higher-forage diet (21.4 percent) and non-forage fiber source diet (21.3 percent).
Dry matter intake was greatest for cows fed the standard diet, intermediate for the non-forage fiber source diet, and lowest for the higher-forage diet. The lower intake for the higher- forage diet likely reflected the higher forage NDF and peNDF content of this diet. The intake of NDF as a percentage of body weight was greater for the higher-forage diet and the non-forage fiber source diet relative to the standard diet. In fact, 1.35 percent of body weight intake of NDF is a very high level of NDF consumption, and consequently the high forage NDF intake may have limited dry matter intake for cows fed the higher-forage diet despite the fact that it was comprised primarily of BMR corn silage. Although milk yield was reduced for cows fed the higher-forage diet, milk fat percentage was elevated, and so solids-corrected milk yield was similar for all diets as was efficiency of solids-corrected milk production.
Total chewing time was greatest for cows fed the higher-forage diet, intermediate for the non-forage fiber diet, and least for the standard diet. Ruminal pH was least for cows fed the standard diet, highest for cows fed the higher-forage diet, and intermediate for the non-forage fiber diet. Finally, microbial protein production was similar for all three diets.
The results of this study show us that we can successfully feed higher-forage diets if the forage contains highly digestible NDF (as in the case of BMR corn silage).
The question remains: how can we best model forage particle dynamics in the rumen to consistently formulate successful high-forage diets? (Note: Elsewhere in the paper, Grant describes efforts of the “Fiber Working Group,” a multi-year collaborative research effort to improve the current nutrition models, with a particular focus on the Cornell Net Carbohydrate and Protein System.)