Responses of fresh cows to three feeding strategies that reduce starch levels by feeding beet pulp.

Abstract

The study objective 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, 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 d in lactation. Experimental diets were a high-starch diet with ground BG (CO; 24.9% starch; 0% BP) and 3 low-starch diets: the CO with BP substituted for ground BG (BB; 19.6% starch; 7% BP), the CO with BP substituted for CS (BC; 20.6% starch; 12% BP), or the CO with BP substituted for CS and ground BG (BCB; 20.3% starch; 12% BP). The CO, BB, BC, and BCB contained 33.4, 34.4, 32.9, and 33.7% NDF, respectively, and 23.1, 22.0, 18.2, and 19.2% forage NDF, respectively. There was no effect of diet on total tract nutrient digestibility ( > 0.20), ruminal pH ( = 0.49), or total VFA ( = 0.39). However, diets affected molar proportions of propionate and acetate ( ≤ 0.01). Relative to CO cows, the molar propionate percentage was less in BB cows ( < 0.01) and tended to be greater in BC cows ( = 0.10), whereas the molar percentage of acetate was less in BC cows than in BB ( < 0.01) and CO cows ( = 0.02). Relative to CO cows (16.50 kg/d), DMI was greater for BC (17.70 kg/d; < 0.01) and BCB cows (17.50 kg/d; = 0.01), but it was less in BB cows (15.60 kg/d; = 0.02). Similar to DMI results, milk yields tended to be greater for BC (37.89 kg/d; = 0.08) and BCB cows (37.81 kg/d; = 0.09) compared with CO cows (35.41 kg/d), but BB cows (33.05 kg/d) tended to produce less milk than CO cows ( = 0.1). Milk fat content tended to be less in BC ( = 0.08) and BCB cows ( = 0.10) than in CO cows. There was no effect of diet on eating and rumination patterns ( ≥ 0.18), except shortened meal intervals for BC and BCB cows compared with CO cows ( = 0.02). Dietary treatments did not affect chewing activities per day or bout ( = 0.50), but BC and BCB cows spent less time on chewing activities per kilogram DM ( < 0.01) and NDF intake ( < 0.01) compared with CO cows. Cows fed the BC and BCB sorted for long particles (>19 mm; < 0.01) but against particles < 1.18 mm ( < 0.01). In the present study, propionate did not seem to play a central role in feed intake regulation of fresh cows, because BB cows had depressed DMI and the lowest molar proportion of propionate. However, reducing starch levels in fresh cow diets by replacing CS and both CS and BG with BP positively affected DMI and milk yield.