Effect of time of cutting and maceration on nutrient flow, microbial protein synthesis, and digestibility in dual-flow continuous culture.

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.