Growth rates and morphological measurements of Porcupine caribou calves

Body weights, leg lengths, and surface area were monitored for bottle-raised barren-ground caribou calves (Rangifer tarandus grand) from the Porcupine herd up to 1 year of age. Body weights were compared with maternally-raised calves from the same cohort in the wild and from the Delta herd. A successful feeding regime for bottle-raising caribou calves is presented.


Introduction
The survival of young ungulates in the Arctic often depends on the interplay between animal vigor and the influence of energetic constraints such as decreased forage resources or increased energy expenditures.Body dimensions and their rates of change are a function of the requirements for energy conservation.Whereas the efficiency of locomotion in young animals increases with body weight and leg length (Parker et al. 1984, Luick and White 1986, Fancy and White 1987), the corresponding increase in body surface area results in an increase in heat loss (Moen 1973:263).The young neonate's level of nutrient intake (e.g., milk composition and volume) plays an important role in the adaptive balance of these cost-benefit functions (White and Luick 1984).
The objective of this study was to measure the changes in body measurements in barren-ground caribou (Rangifer tarandus granti) raised under controlled conditions to gain an understanding of the post-natal adaptability of this northern species.

Methods
Fourteen barren-ground caribou calves were obtained between 3 and 4 June 1987 from the Porcupine herd on calving grounds near Beaufort Lagoon, Arctic National Wildlife Refuge, Alaska.The animals, which were 1-2 days of age, were flown to the Large Animal Research Station (LARS), Institute of Arctic Biology, University of Alaska Fairbanks.Calves were initially raised in groups of 4 or 5 in small disinfected wooden stalls inside an unheated barn; concrete floors were covered with wood shavings.At 1.5 months of age, animals were placed in outdoor fenced pens (4.8 x 4.9 m) seeded with brome grass, containing a sheltered feeding and bedding area of wood shavings.The calves were allowed to run as a group several times daily in a larger paddock (5.0 x 29.3 m) adjacent to the smaller pens.
A milk formula was prepared similar to that used by Parker and Wong (1987) of homogenized whole cow's milk and lamb milk replacer (Land O' Lakes, Minneapolis, MN).The amount of air-dry replacer added to cow's milk was 10% of the milk weight.Powdered casein (3% of the milk weight; Erie Casein Co., Erie, IL) was also added to the formula.Estimates of dry matter, fat, and protein for this formula were 20.4%, 6.1%, and 5.1%, respectively; these estimates are all less than average values determined for Rang-ifer species (White and Luick 1984).A child's vitamin with iron supplement was crushed and added to the milk once daily.
The caribou calves were initially bottle-fed 5 times daily at a volumetric rate similar to that prescribed for black-tailed deer (Parker and Wong 1987).Immediate dietary-induced diarrhea occurred, however, and feeding times were increased to 7 daily (between 05.30 and 01.00) to accommodate the lactational strategy of a follower species (Carl and Robbins 1988).Volumes fed were reduced for each individual to levels that could be tolerated without gastrointestinal disturbance.Within 1-2 weeks, all animals were habituated to the dietary formula.Total daily amounts offered were increased until the first week of July, from which time onwards milk volumes and the number of feedings were reduced gradually.Animals received only 150 ml once daily by 5 September.This volume was slowly replaced with water and fed until 6 December to maintain and reinforce the social interaction with handlers.A summary of the successful feeding regime for all caribou calves is presented in Figure 1  cess to brome pasture.Ground-growing lichens collected from nearby tundra areas were used as reward incentives.
Animals were weighed at 4 to 7-day intervals.Twenty-two body-surface measurements were taken to the nearest cm on standing, full-fed animals once or twice per month to calculate surface area (Moen 1973:263, 436).These values included circumferences and lengths of the nose, face, neck, ears, front and rear legs, and body.Brisket height, carpus or front knee height, and tarsus or hock height were also measured from the ground to the nearest cm and correlated with body weight.Four male calves were included in all measurements up to 2.5 months of age.Data gathered after this date (15 August 1987) were for female calves only.
Predictive curves for all variables were determined by nonlinear regression techniques (Dixon 1981).Differences in body weights of these Porcupine calves were compared graphically with Beverly Lake calves and with Delta calves using analyses of covariance.Tests of significance were at P<0.05.

Growth rates
Body weight increased rapidly until approximately 170 days of age (Fig. 2).Growth rates plateaued in mid-November and then increased again in late April.
Very limited data exist on the growth rates of free-ranging caribou calves.A few values presented by McEwan (1968) suggest that growth rates of very young wild barren-ground caribou calves (Rangifer tarandus groenlandicus) from Beverly Lake, Northwest Territories, Canada did not differ from those of maternally-raised calves from the same herd kept in captivity.After 5 months of age, however, the captive calves continued to gain weight while wild calves lost weight and were restricted in growth throughout the following summer.Growth rates of the hand-reared Porcupines calves of this study up to 3 months of age were similar to those noted above.After 5 months of age, they were all larger than both wild and captive barrenground caribou calves from Beverly Lake.
Eight weights of maternally-raised calves from the same Porcupine herd cohort (K.R. Whitten, unpub.)showed that at approximately 93 days of age, 2 field-caught calves (Old Crow, Yukon Territory) were of very similar weights (34.0, 36.7 kg) and 2 (45.4,47.9 kg) were 10 to 15 kg heavier than the hand-reared animals.At approximately 176 days of age, all field-caught calves (52.3, 53.2, 53.2, and 54.6 kg; Eagle Plains, Yukon Territory) were within the weight range of the bottle-raised calves.This comparison should be qualified in that the age of the free-ranging animals was not known but was based on the average calving date for this herd (3 June).Nonetheless, the feeding and rearing conditions of the caribou calves in this study appear equivalent with respect to weight development to those raised naturally.Furthermore, adverse environmental constraints do not appear to have influenced the growth rates of free-ranging calves before 6 months of age.

Figure 1 .
Figure 1.Milk volumes fed to Porcupine caribou calves in relation to age and body weight.Numbers at the top of the figure indicate number of feedings per day.

Figure 2 .
Figure 2. Body weight in relation to age of bottleraised Porcupine caribou calves.Data are individual weights of 14 calves.