Effects of forage nutritional quality (energy and protein) on deer acceptance of foods containing secondary metabolites

Deer foraging on tree seedlings is recognized as the most widespread detriment to reforestation efforts. Non-lethal approaches to reduce deer damage to seedlings are highly desirable. Avoidance of natural secondary metabolites contained in conifers may provide feasible means to develop non-lethal measures. Other studies have demonstrated that sheep and goats fed diets with high protein-to-energy ratios, or allowed to select between concentrates high in either energy or protein, ate much more of a high-terpene diet and of a high-tannin diet than when they were fed diets high in energy-to-protein ratios. Thus, manipulating foraging options for deer may impact their ability to ingest terpenes contained in conifers. We conducted a series of studies to determine whether deer acceptance of terpene-containing foods can be affected by altering the ratio of energy and protein in their maintenance diet. We determined relative consumption of a high-energy and low-protein diet, and a low-energy and high-protein diet, when deer are given the opportunity to self-regulate their intake. We also determined if deer modified their relative intake of these diets when offered an alternative terpene-treated diet. Penned deer were offered variable diets (e.g., high energy-low protein, low-energy-high protein, or both foods), then their acceptance of terpene- and tannin-containing foods was determined. Deer consumed more and demonstrated a strong preference for the high-energy diet relative to the high-protein diet. However, the varied diets did not appear to affect their intake of terpene or tannin-containing foods. This paper discusses the potential of manipulating maintenance rations as a non-lethal tool, presents initial results and possible explanations for differences between our study with deer and prior work with domestic ruminants.