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A study of comparative growth in four races of black-tailed deer Bandy, Percy John

Abstract

Four racial stocks of Black-tailed deer, captured as fawns in their native habitat, were raised under controlled nutritional conditions at facilities of the University of British Columbia. Qualitatively complete liquid and solid diets were fed isocallorically on two planes of nutrition; a high plane designed to evoke expression of the maximum genetic potential for growth; a low plane designed to reduce growth to a minimum. Body weights and certain linear measurements were recorded at intervals and the resultant data were used for comparisons of growth parameters related to sex, plane of nutrition and racial origin. Weight growth curves were found to fluctuate seasonally in correspondance to changes in physiological conditions associated with reproduction. In addition, it was found that growth in both sexes was suppressed by the winter environment in spite of constancy in the daily diet. Low plane deer showed positive growth responses during the winter thereby indicating that growth is not suppressed to the same degree in animals which have not attained their seasonal maximum weights through undernourishment. Linear growth curves exhibited no seasonal depressions as they increased continuously from birth to their respective mature sizes. In contrast to body weight, the mature size of all linear measurements, except chest girth were not significantly affected by the plane of nutrition. The rates of growth, however, were reduced by the low plane thereby increasing the age at which mature size was attained. The relative proportions at mature size of linear measurements were not affected by the plane of nutrition. Slight alterations in proportions were noted for several ratios but the only significant difference occurred in the chest girth/hind leg length ratio. The development of significant differences between planes of nutrition with regard to this ratio indicates that it might be useful in quantitatively determining condition in wild populations. Significant sexual differences in the head length/head width ratio at maturity showed that the head length did not differ in size whereas the remaining measurements were reduced in magnitude for female deer. Thus the components of head length appear to escape the limitations imposed by the female upon growth of all other parts measured. Parameters of growth such as the instantaneous relative rate of growth, the instantaneous relative rate of decline in growth, mature size, age and weight at inflection, age at maturity, and others have been computed for each race, sex and plane of nutrition. Parameters derived from the growth patterns of all four races demonstrate that each race differs from the others in one or more aspects of their growth response in a given set of environmental conditions. The Mule deer is potentially the largest and fastest growing, followed in turn by the Sitka Black-tail, the Californian stock and the Vancouver Island stock of the Columbian Black-tailed deer. This and other characteristics of growth indicate that the Californian and Vancouver Island stocks of the Columbian Black-tailed deer may be separable at the sub-specific level. No racial differences could be shown, however, in the efficiencies of the growth processes.

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