Increases in grain prices have led to renewed interest in feeding reduced-starch diets to lactating dairy cows. An experiment was conducted to determine the effects of altering carbohydrate sources and reducing dietary starch on lactational performance, feeding behavior, and ruminal measures of Holstein dairy cows. Fifteen multiparous cows (6 ruminally cannulated) were blocked and assigned to 1 of 5 squares and used in a replicated 3×3 Latin square design with 21-d periods. Cows were fed 1 of 3 experimental diets: a control diet containing 20% brown midrib corn silage, 20% conventional corn silage, and 10% hay crop silage (CON); a reduced-starch high-forage diet containing 53% brown midrib corn silage and 10% hay crop silage (HFOR); and a reduced-starch diet containing the same forages as CON with partial replacement of corn meal by nonforage fiber sources (HNFFS). The CON diet contained (% of dry matter) 26.0% starch and 34.7% neutral detergent fiber (NDF), whereas the HFOR and HNFFS diets contained 21.4 or 21.3% starch and 38.3 or 38.0% NDF, respectively. Dry matter intake tended to be greater for cows fed the CON diet (28.2 kg/d) compared with those fed the HFOR diet (27.2 kg/d). Dry matter intake for cows fed the HNFFS diet was intermediate (27.7 kg/d). Milk yield was greater for cows fed the CON diet (51.6 kg/d) compared with those fed the HFOR diet (48.4 kg/d), but milk fat content tended to increase for cows fed the HFOR diet (3.98%) compared with those fed the CON diet (3.66%). Consequently, fat-corrected and solids-corrected milk yields were unaffected by dietary treatments. Total chewing, eating, and rumination times were similar across all dietary treatments. Rumination time per kilogram of DM was greatest for the HFOR diet, intermediate for the HNFFS diet, and least for the CON diet, whereas rumination time per kilogram of NDF was greatest for the CON diet and least for the HNFFS diet. Mean ruminal pH, NH3-N (mg/dL), and total volatile fatty acid concentrations (mM) were similar across all dietary treatments. Molar proportion of ruminal acetate (mol/100 mol) was increased for cows fed the HFOR diet compared with cows fed the CON diet. Microbial N yield measured by urinary purine derivatives was unaffected by dietary treatment. Reduced-starch diets containing greater amounts of high quality, highly digestible forage or nonforage fiber sources in place of corn meal resulted in similar fat-corrected or solids-corrected milk yield for high-producing dairy cows in the short term.
Maceration and evening-cutting are 2 forage management techniques that have independently improved forage quality and nutrient utilization in ruminants, but have not been evaluated in combination. Using a dual-flow continuous culture fermenter system, this preliminary study was designed to evaluate the individual and combined effects of time of cutting and maceration on in vitro ruminal digestion, nutrient flows, and microbial protein synthesis. Forages were harvested as hay from a timothy (Phleum pratense L.)-birdsfoot trefoil (Lotus corniculatus L.) stand in the morning (AM) or evening (PM). Half of each morning- and evening-cut treatment was macerated (AM-M, PM-M). The chemical composition (DM, OM, CP, NDF, ADF), including nonstructural carbohydrates (NSC) and water-soluble carbohydrates (WSC), was determined for each of the 4 treatments (AM, AM-M, PM, PM-M). Forages were ground to 2 mm and allocated to separate fermenters at 60 g of DM/d in a 4 × 4 Latin square design. Fermenters were operated over four 10-d periods with the first 7 d for adaptation followed by 3 d of sampling. Evening-cutting enhanced the apparent digestibility of NDF (P = 0.02) and ADF (P = 0.006), with a tendency (P < 0.10) for improved true DM digestibility and microbial protein synthesis. Molar proportions of individual VFA were not affected (P > 0.10) by time of cutting, though evening-cutting increased (P = 0.02) total concentration of VFA. Maceration had no effect (P > 0.10) on true nutrient digestibility or microbial protein synthesis. An interaction of time of cutting and maceration (P < 0.05) was observed whereby maceration decreased true DM and OM digestibilities in evening-cut treatments, but had no effect in morning-cut treatments. Similarly, maceration reduced total N supply (P < 0.001) and molar proportions of acetate (P = 0.04) and increased molar proportions of propionate (P = 0.01) in evening-cut treatments with no effect on morning-cut treatments. These results indicate that independent use of evening cutting increased fiber digestibility and total VFA concentration, and independent use of maceration shifted molar proportions of VFA toward glucogenic fermentation. The combined use of these management techniques afforded no improvement for in vitro digestibility or metabolism when applied to morning-cut hay, and decreased nutrient digestibility when applied to evening-cut hay. Due to inherent limitations of in vitro systems, the results of this study should be interpreted with caution. Further in vivo studies are needed to support our conclusions.
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