Dry Matter and Energy Intake in Relation to Digestibility in White-Tailed Deer

Abstract

Two digestion-intake trials were eonducted with 24 male and female white-tailed deer (Odocoileus virginianus) fawns during January, February, and Mareh 1971. Within eaeh trial deer were randomly assigned to one of six treatments representing a basal diet diluted with oak sawdust in levels of 0, 15, 25, 30, 35, and 45 pereent. Dry matter (DM) digestibility and the digestible energy (DE) eontent ( keal DE/gram ) were highly eorrelated with the pereent dilution. Dry matter intake (grams/BW[kg body weight]0 75/day) inereased as digestibility deereased from a high of 3.44 keal DE/gram to 2.17 keal DE/ gram; below this point intake deereased. Digesftible energy intake ( keal DE/BW0 75/day + SE ), on the other hand, remained relatively eonstant (155.2+7.46) keal above 2.17 keal DE/gram. The data indieate that these animals were able to maintain a constant energy balanee, elose to the maintenanee requirements of fawns, by adjusting dry matter intake when fed diets of medium to high digestibility (DE > SO pereent ) . Below 2.17 keal DE/gram, energy intake deereased with the decrease in dry matter intake. The point (2.17 keal DE/gram) representing the interseetion of two regression lines for DM intake versus keal DE/gram of feed was taken to be the threshold at whieh digestive traet fill began to limit the dry matter and energy intake of these animals. These results are diseussed in terms of a theoretieal model of the intake mechanism of ruminants. J. WILDL. MANAGE. 37(2): 95-20 Z Studies of domestic ruminants have shown thatn for diets of low digestibility, there is a positive correlation between voluntary dry matter intake and digestibility. For highly digestible diets, there is a negative correlation ( Blaxter et al. 1961, Conrad et al. 1964). Montgomery and Baumgardt (1965) (Fig. 1) have examined this phenomenon and constructed a model of the intake regulatory mechanism of ruminants. According to this model, various feeds can be thought of as points on a continuum from low to lligh digestibility. Ruminants are able to regulate dry matter intake over a wide portion of this continuum so that their energy 1 Published with lie approval of the Director of ie Pennsylvania Agricultural Experiment Station as Journal Article No. 4186. Authorized April 17, 1972. Supported in part by U.S. Forest Service, Northeastern Forest Experiment Station Contract No. 23-()0-124, Supplement No. 16, and the Pennsylvania Game Gemmission. Paper number lS9 of the Pennsylvania Cooperative Wildlife Research Unit. intake remains equal to their need. At the igh r levels of digestibility, this is done by increasing intake as digestibility decreases, explaining the negative correlation between digestibility and intake observed at high levels of digestibility. As digestibility further decreases, a point is reached where the animal is eating to the maximum capacity of the digestive tract. This point is the threshold where digestive tract fill begins to limit intake. Above this threshold the animal is able to increase its intake for each decrease in digestibility. Below this threshold (all or a part of) the digestive tract remains filled to capacity, but as the digestibility of the feed decreases so does the rate of passage. The effect is decreased intake for each decrease in digestibility. For a given animal the location of the fill threshold along the continuum of digestibility depends on its energy requirements. For maintenance the threshold assumes its lowest value, below which the animal enters J. Wildl. .Manage. 37(2):1973 195 This content downloaded from 157.55.39.158 on Fri, 18 Nov 2016 04:12:27 UTC All use subject to http://about.jstor.org/terms Table 1. Ingredients of the basal diet.