Abstract
We added antler growth and mineral metabolism modules to a previously developed energetics model for ruminants to simulate energy and mineral balance of male and female caribou throughout an annual cycle. Body watet, fat, protein, and ash are monitored on a daily time step, and energy costs associated with reproduction and body mass changes are simulated. In order to simulate antler growth, we had to predict calcium and phosphorus metabolism as it is affected by antler growth, gestation, and lactation. We used data on dietary digestibility, protein, calcium and phosphorus content, and seasonal patterns in body mass to predict the energy, nitrogen, calcium, and phosphorus balances of a "generic" male and female caribou. Antler growth in males increased energy requirements during antler growth by 8 to 16%, depending on the efficiency with which energy was used for antler growth. Female energy requirements for antler growth were proportionately much smaller because of the smaller size of female antlers. Protein requirements for antler growth in both males and females were met by forage intake. Calcium and phosphorus must be resorbed from bone during peak antler growth in males, when > 25 g/day of calcium and > 12 g/day of phosphorus are being deposited in antlers. Females are capable of meeting calcium needs during antler growth without bone resorption, but phosphorus was resorbed from bone during the final stages of antler mineralization. After energy, phosphorus was most likely to limit growth of antlers for both males and females in our simulations. Input parameters can be easily changed to represent caribou from specific geographic regions in which dietary nutrient content or body mass patterns differ from those in our "generic" caribou. The model can be used to quantitatively analyze the evolutionary basis for development of antlers in female caribou, and the relationship between body mass and antler size in the Cervidae.
Highlights
Antlers are among the most striking features of the Cervidae
We have developed and validated a model which is adaptable with respect to ruminant species, and which can simulate the energetic costs of gestation and lactation (Moen et al, 1997)
The Energetics and Activity Simulation Environment (EASE) model was designed to accept "plug-in" modules which simulate processes other than energy metabolism, such as a spatially-explicit foraging model (Moen et al, 1997; 1998), nitrogen metabolism (Moen & DelGiudice, 1997), and the antler growth model described in this manuscript
Summary
Antlers are among the most striking features of the Cervidae. Despite the importance of antlers to behavior and evolution of cervids, very little work has been done on the nutritional physiology of antler growth (Goss, 1995). A further complication is that it would be desirable to use an experimental protocol which could monitor the status of energy, protein, and mineral metabolism simultaneously on Rangifer, Special Issue No 10, 1998 several individuals. Such experiments quickly become technologically challenging and prohibitively expensive. Swift's model could simulate many ruminant species with adequate parameterization, but did not implement costs of productive functions such as lactation or antler growth. We have developed and validated a model which is adaptable with respect to ruminant species, and which can simulate the energetic costs of gestation and lactation (Moen et al, 1997)
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