Effect of Inoculum Source on in Vitro Digestion of Deer Foods

Abstract

Comparative in vitro digestion trials were conducted with inoculum obtained, via rumen fistula, from a white-tailed deer (Odocoileus virginianus) and a nonlactating Jersey cow to determine the feasibility of using cattle inoculum for predicting in vivo digestibility of deer foods. A modification of the basic two-stage Tilley and Terry technique was used to evaluate four substrates covering a wide range of digestibilities. These were white cedar (Thuja occidentalis), fire cherry (Prunus spp.), timothy hay, and the standard ration fed at The Pennsylvania State University deer research facility. The mean in vitro values ranged from 38.4 percent for cherry to 86.1 percent for the deer ration. Digestibilities obtained with the deer as the inoculum source were quite variable but were not significantly different from values obtained with cow inoculum when tested by analysis of variance. Three of the substrates, cedar, timothy, and deer ration, had been fed previously to deer in conventional digestion trials. In vitro runs with cow inoculum were conducted with two additional substrates of known deer in vivo digestibility, crownvetch hay (Coronilla varia) and red clover hay. The in vitro results obtained with cow inoculum were further analyzed by regression and correlation. A highly significant correlation coefficient (r = 0.99) was shown between cow in vitro and deer in vivo values. It was concluded that the in vitro digestion technique, with the cow as the inoculum source, can be used to estimate accurately digestibilities of deer foods. J. WILDL. MANAGE. 40(2):301-307 Nutrient availability is a major factor affecting the carrying capacity of deer ranges. The diet of wild deer is made up of a variety of foods ranging from highly digestible fruits and seeds to browse of low nutritive value. If a given deer range is to be managed properly, the food of the deer must be evaluated qualitatively and quantitatively. Evaluation of foods by means of conventional digestion trials is expensive and time consuming and requires large amounts of foods; collection of sufficient browse would be extremely difficult. Also several investigators (Dietz et al. 1962, Ullrey et al. 1964, Mautz 1971, Ammann 1973) have encountered problems in using deer in digesti n trials. Therefore, it seems logical to examine the in vitro digestion technique as a method for evaluating deer foods. In vitro digestion techniques have gained ide acceptance and are being used extensively to evaluate forages for domestic ruminants. Several investigators (Johnston t al. 1968, Urness 1969, Ward 1971, Torgerson and Pfander 1971, Snider and Asplund 1974, Robbins et al. 1975) have conducte in vitro digestion trials using woody substrates. However, none of these researchers used a technique specifically adapted to the digestion of woody samples. Mell nberger et al. (1970) modified the Tilley and Terry (1963) technique specifically to optimize digestion of treated and untreated woods. Ammann (1973:93) tested the combined effect of several variables on the in vitro digestion of deer browse and concluded that a modification of the Tilley and Terry technique was nec1Published with the approval of the Director of the Pennsylvania Agricultural Experiment Station as journal article no. 4921, authorized 18 August 1975. Supported in part by the Pennsylvania Game Commission. Paper no. 200 of the Pennsylvania Wildlife Research Unit. J. Wildl. Manage. 40 (2):1976 301 This content downloaded from 157.55.39.221 on Mon, 03 Oct 2016 05:18:18 UTC All use subject to http://about.jstor.org/terms 302 INOCULUM SOURCE AND IN VITRO DIGESTION *Palmer et al. essary to reduce sample variation to an acceptable level. The use of domestic ruminants, rather than deer, would greatly facilitate the in vitro digestion technique in that it would eliminate problems associated with the deer as a living rumen fluid donor or the necessity of sacrificing an animal (Urness 1969, Short 1971, Ward 1971) when inoculum is needed. The purpose of this study was to determine the feasibility of using cattle as the inoculum source for in vitro digestion of deer foods, with a technique specifically modified for browse, and to determine whether this in vitro technique could be used to predict accurately the in vivo digestibility of deer foods. We wish to thank K. R. Bennett for assistance with the statistical analysis of the data, M. A. Ondik and R. C. Mothersbaugh for help in handling the deer, and the Pennsylvania Game Commission and the Pennsylvania Wildlife Research Unit for the use of the deer. MATERIALS AND METHODS