Effect of Shredding Alfalfa on Cellulolytic Activity, Digestibility, Rate of Passage, and Milk Production a

A series of trials was performed with sheep and goats to compare mechanically shredded with conventionally (control) harvested alfalfa hay. Shredded hay tended to contain less CP and more cell wall constituents than the control; digestibility of NDF in vitro also was increased by shredding. Intake of DM and digestibilities of NDF and ADF were increased in sheep fed shredded hay. Digestibilities of DM and CP were similar between treatments. Total tract digestibilities determined using acid detergent lignin and Yb as internal and external markers were similar to those obtained by total collection. There was no effect of shredding on rate of passage and total mean retention time of hay in the digestive tract of sheep. Ruminal pH and VFA were not altered by shredding of hay. However, production of 4% FCM and milk protein content was increased in goats fed shredded hay. Shredded hay suspended in the rumen in situ had higher p a r t i c l e a s s o c i a t e d c a r b o x y m e t h y l cellulase activity throughout the incubation period than did control hay. The enzyme activity was maximal at 6 h and declined thereafter for both hays. The pattern of particle-associated carboxymethylcellulase activity was similar to that of NDF digestion in vitro. Received July 6, 1987. Accepted December 16, 1987. 1Mention of commercial products in this paper does not constitute endorsement by the USDA or the ARS. 2Present address: Department of Dairy Science, Kangweon National University, Chuncheon 200, Korea. B. J. HONG, 2 G. A. BRODERICK, R. G. KOEGEL, K. J. SHINNERS, and R. J. STRAUB US Dairy Forage Research Center USDA, ARS and University of Wisconsin 1925 Linden Drive West Madison 53706 I N T R O D U C T I O N Numerous approaches have been investigated to maximize utilization of forages by ruminants. Mechanical treatments, such as ball milling or grinding of forage, increase surface area and solid structure cracks, and decrease degree of crystallinity of cellulose (23). Mechanical t reatments increase the rate of acid hydrolysis but do not significantly alter enzymatic hydrolysis of the cellulose (23). Maceration or shredding of alfalfa forage increases the rate of drying relative to conventionally conditioned forage (26). The shredding process also results in separation of stems into numerous fibrous pieces while severely damaging the waxy cuticle (26). This yields both greatly increased surface area and reduced resistance to moisture loss from the stem. Entry of microbes into plant material is primarily via damaged surfaces and natural openings such as stomata (3). The rate of microbial attack on insoluble substrates is proport ional to the surface area exposed (18). Mechanically shredding (macerating) alfalfa stems increased both the rate and extent of NDF digestion in vitro (14). Scanning electron microscopy (SEM) revealed that shredding caused separation of lignified and unlignified cells, damaged plant structural integrity, and increased colonization by mixed rumen microorganisms of the luminal surface of cell walls (14). Cellulolytic activity and DM digestibility are highly correlated in untreated and ammoniatreated straw (28); therefore, the relationship of particle-associated microbial enzyme activity to microbial at tachment may be a promising way to evaluate the effectiveness of shredding of hay on ruminal digestibility. There has been no previous published research on the effects of mechanically shredding alfalfa on in vivo digestibility. Hence, the 1988 J Dairy Sci 71:1546-1555 1546 UTILIZATION OF SHREDDED ALFALFA 1547 objectives of this study were to determine the effects of shredding alfalfa forage on: 1) digestibility, rate of passage, weight gain, and milk production; and 2) cellulolytic activity of particle-associated rumen microbes. MATERIALS AND METHODS