PHOSPHORUS-NUTRITION IN WHITE-TAILED DEER - NUTRIENT BALANCE, PHYSIOLOGICAL-RESPONSES, AND ANTLER GROWTH

Phosphorus (P) is considered, except for sodium, to be the most limiti ng mineral for growth and reproduction in large mammalian herbivores w orldwide and a predictor of ungulate distribution and abundance. Knowl edge of phosphorus nutrition and seasonal adaptation to dynamics in mi neral needs and availability in wild herbivores is incomplete. This pa per reports data on experiments designed to evaluate physiological res ponses to low dietary P and to determine phosphorus requirements in ma le white-tailed deer (Odocoileus virginianus), a browsing cervid with presumed elevated mineral requirements during antlerogenesis. Adult (g reater-than-or-equal-to 2 yr) male deer were housed individually and p laced on three levels of dietary P (0.14-0.19%, 0.24-0.27%, and 0.34-0 .36% of diet dry mass) from June 1989 to September 1991. We conducted balance trials to measure seasonal P retention and to model annual and seasonal dietary P requirements. Data were collected on serum chemist ry, endocrine function, antler growth, antler composition, and tail bo ne composition in two trials designed to test the hypothesis that P is limiting to deer antler growth in southwestern habitats. Phosphorus b alance varied by diet and tended to fluctuate seasonally. Retention wa s highest for the 0.19% P diet and greatest during the fall. The varia tion in P balance resulted from increased efficiency in P metabolism i n animals on the 0.14-0.19% P diet. Dietary phosphorus requirements we re estimated at 72.2 mg.kg-0.75.d-1 (0.14% P at study intake rates) on an annual basis, changing seasonally from 94.4 mg.kg-0.75.d-1 (0.16%) during spring to 57.4 mg.kg-0.75.d-1 (0.11%), and 59.6 mg.kg-0.75.d-1 (0.12%) during summer and fall, respectively. Feed consumption, body mass, antler size and composition, and bone composition did not vary b y diet. Diet x month interactions were observed in 1990 and 1991 for s erum activity of alkaline phosphatase (AP), manifested in higher activ ity on the 0.14-0.19% P diet during the peak period of antler growth. Changes in AP were an indicator of physiological compensation to low d ietary P. Other key serum chemistries and hormonal concentrations did not vary by diet. These results suggest that P limitation for antler g rowth is unlikely for adult browsing cervids. We predict sensitivity o f the distribution and abundance of male cervids to P limitation to be a function of feeding strategy and body size.