Abstract

The objective of this study was to evaluate the effects of reducing dietary starch content in fresh cow diets while maintaining NDF levels by substituting barley grain (BG), corn silage (CS), or both with beet pulp (BP) on nutrient digestion, ruminal fermentation, dry matter intake (DMI), lactation performance, meal patterns, chewing activity, and sorting behavior. Thirty-six multiparous cows were randomly assigned to 1 of 4 experimental diets from calving to 21 days in lactation. Experimental diets were a high-starch diet with BG ground (CO; 24.9% starch; 0% BP) and 3 low-starch diets where BP substituted for either BG (BB; 19.6% starch; 7% BP), CS (BC; 20.6% starch; 12% BP) or CS and BG (BCB; 20.3% starch; 12% BP). The CO, BB, BC, and BCB diets contained 33.4, 34.4, 32.9, and 33.7% total neutral detergent fiber (NDF) and 23.1, 22.0, 18.2, and 19.2% forage NDF, respectively. There was no effect of diet on total tract nutrients digestibility (P > 0.20), ruminal pH (P = 0.49), or total VFA (P = 0.39). However, diets affected molar proportions of propionate and acetate (P < 0.01). Relative to CO cows, molar propionate percentage was lower on BB cows and tended to be higher on BC cows, whereas molar acetate percentage was lower on BC cows than BB and CO cows. Relative to CO cows, DMI was higher for BC (1.2 kg/d) and BCB (1.0 kg/d) cows, while it tended to be lower on BB (1.1 kg/d) cows. According with intake results, milk yields tended to be 2.5 and 2.4 kg/d greater for BC and BCB cows relative to CO cows, but BB cows tended to produce 2.4 kg less milk than CO cows. Milk fat content tended to be lower in BC and BCB cows than in BB and CO cows. There was no effect of diet on eating and rumination patterns (P > 0.18), except shortened meal intervals for BC and BCB cows compared to CO cows. Dietary treatments did not affect chewing activities per day or bout (P = 0.50), but BC and BCB cows spent less time on chewing activities per kg of DM and NDF intake compared to CO cows. Cows fed BC and BCB sorted for long particles (>19 mm) but against particles on the bottom pan. In our study, propionate did not seem to play a central role in feed intake regulation of fresh cows, as BB cows had depressed DMI and the lowest molar propionate proportion. However, reducing starch levels on fresh cow diets by replacing CS, and CS and BG, with BP positively affected DMI and milk yield.