Digestive Capacity and Diets of White-Tailed Deer and Exotic Ruminants

Abstract

We collected 20 axis deer (Axis axis), 15 white-tailed deer (Odocoileus virginianus), 14 blackbuck antelope (Antilope cervicapra), 14 sika deer (Cervus nippon), and 11 fallow deer (Dama dama) in the Edwards Plateau Region of central Texas during 21 May-22 July 1986. Relative ruminoreticular capacity, an index of digestive capability, varied (P 93% grass; and sika deer consumed near equal amounts of grass and forbs. Percent crude protein of rumen contents for each species paralleled the amount of forbs consumed. J. WILDL. MANAGE. 52(4):595-598 Wild exotic ungulates introduced into Texas in the early 1930's have increased to 120,129 animals representing 59 species by 1984 (Traweek 1985). The competitive advantage that some exotic ungulates appear to have over white-tailed deer has been related to the general feeding strategy of exotics. Exotics apparently can shift to a diet of grasses when preferred browse and forbs decrease in abundance, but white-tailed deer are stressed by nutritional deficiencies associated with grass consumption (Baccus et al. 1985). Gut morphology, rumen motility, and body size limit the range of foods an animal can efficiently assimilate (Kay et al. 1980). Size of the ruminoreticulum relative to body weight determines digestive capabilities of a species. The ruminoreticulum :body weight ratio is a useful index to a species' potential diet selectivity and digestive capability (Hanley 1982). Our objective was to compare relative ruminoreticular capacity among white-tailed deer and 4 of the most prevalent exotic ruminants in Texas: axis deer, sika deer, fallow deer, and blackbuck antelope. Species that are better adapted to a grass or roughage diet should have a larger relative ruminoreticular capacity than species adapted to a forb or concentrate diet. Relative ruminoreticular capacity is then related to diet and protein content of the rumen