Composition and potential utilization of crop residues and forages within the digestive tract of ruminants as predicted by laboratory techniques
The purpose of the present research was to determine the nitrogen (N) and mineral composition of selected forages (alfalfa, canarygrass, bromegrass, fescue, whole plant corn silage and elephant grass silage), crop residues (corn, oat, and soybean), and crop residue plant parts, as well as to evaluate the potential utilization of dry matter (DM), N, and some mineral elements, making use of laboratory techniques;The highest concentrations of mineral elements (Ca, K, Mg), determined by the dry ash method, were observed when forage feeds and crop residues were ashed at 550 C for 1.5 h. In general, crop residues were low in crude protein (CP) (< 5%), digestibility of DM (< 50%), P (< .1%), and perhaps some trace elements (Zn, Mn, and Cu). The low content of these nutrients in crop residues is in contrast to the higher level observed in more immature whole-plant forage feeds;Amylase, cellulase and protease enzymes were not effective in solubilizing DM of samples. Pretreating the samples with .2% pepsin-HCl at 40 C, previous to their incubation with cellulase, resulted in increased (P < .01) disappearance of DM and CP. These results were comparable to those obtained with the nylon bag-pepsin technique. However, the amounts of DM solubilized by cellulase enzymes varied with the origin (chemical company) of the enzymes;The nylon bag technique consisted of exposing feeds for digestion in the rumen of fistulated cattle. Repeatable results, comparable to literature values, were obtained using either nylon or dacron cloth of at least 30 micron pore size. In short-term studies (< 24 h), sample weight needed to be kept under 20 mg/cm('2) of bag surface area. Inherent losses of particulate matter through the bag cloth varied from 2 to 14%. A correction factor for this efflux of particulate matter was used. Nitrogen, Ca, Zn and Mn disappearance from bags seemed to follow the DM disappearance of the respective feed sample, while that of Mg, P and K appeared to be more related to the water-soluble fraction. The residues remaining in the bag after rumen digestion appeared contaminated with bacteria, at times, based upon the negative disappearance of CP, P, Zn, and Mn of crop residues from nylon bags;Results of laboratory techniques were discussed with respect to in vivo utilization of feeds and crop residues.