Digestion dynamics in white-tailed deer

Abstract

Thirteen standard metabolism trials were conducted from May 1986 to June 1987 with white-tail deer (Odocoileus virginianus) utilizing a pelleted diet or one of 3 browse species (guajillo, Acacia berlandieri; blackbrush acacia, Acacia rigidula; and brazil, Condalia obovata. Results support the hypothesis that deer are adapted to eating browse because of their ability to easily digest cell solubles and rapidly remove indigestible particulate matter. Results do not support the hypothesis that deer maximize phosphorus (P) digestibility at the expense of other nutrients to meet their P requirements. Dry matter intake(DMI) varied seasonally and was related positively to compartment turnover rate and negatively to the amount of cell wall in the diet. Mean in vivo dry matter digestibility (DMD) for the pelleted diet was 75.6%. Because of small condensed tannin (7.83 mg/g), lignin (2.62%) and neutral detergent fiber bound nitrogen (NDFN) levels (7 .88%), protein and neutral detergent fiber (NDF) digestibilities in the pellet diet were high, 73.2% and 81.7%, respectively. Seasonal DMD for guajillo varied from 48.1% in the early spring to 35.2% in late summer. Blackbrush and brazil mean DMD were 36.3% and 49.1% respectively. Digestibility of the crude protein (CP) in guajillo varied from 45.8% in early spring to 13.7% in late summer. Low DMD and CP digestibilities were related to high condensed tannin (89.9 to 117.9 mg/g), and NDFN (46.2% to 54.0%) levels. Digestible energy (DE) was highly correlated with DMD (R2 = 0.99) for all diets. Mineral digestibilities were low for each diet except P which had strongly negative digestibilities. Turnover rates were slowest (17 to 21%/hr) in those diets which were more highly digested. Total tract mean retention time (MRT) was fastest in the late summer guajillo diet (37.1 hours) which was the least digested diet. The standard 2-stage in vitro technique accurately predicted in vivo dry matter, energy, and protein digestibilities with confidence, R2 = 0.89, 0.92, 0.93, respectively.