Nutrition-Growth Relations of Elk Calves during Late Summer and Fall

Abstract

We report nutrition-growth relations in juvenile Rocky Mountain elk (Cerous elaphus nelsoni) from mid-August through mid-November. Data were generated from 3, 18-day experimental trials in 1993 with 42 calves, and from general feeding and growth data collected in 1991 with 25 calves. Intake of digestible energy was linearly correlated with growth rate and accounted for 53-89% of the variation in calf growth. Maximum daily digestible energy intake and growth rates were 368 kcal/kg BM 0.75 and 0.70 kg/day in late August and early September and 342 kcal/kg BM 0.75 and 0.33 kg/day in mid-November. Intake-specific growth rates declined after late September, suggesting a seasonal influence on growth-intake relations. We developed a deterministic model of growth to compare body mass dynamics over autumn of calves on an optimum diet (i.e., 3.3-2.95 kcal of digestible energy/g of forage) versus calves on diets available to free-ranging elk (2.66-1.86 kcal/g). Model projections indicated a 21% difference in body mass of the 2 groups by mid-December due to the lower concentration of digestible energy in diets of free-ranging calves. Our results confirm the importance of nutrition in late summer and fall for growth of elk calves, suggest a mechanism linking dietary quality during this time to winter survival, and demonstrate the importance of evaluating forage quality for reliable assessment of habitat quality on elk summer and autumn ranges.