Nitrogen excretion in the deer in relation to age and metabolic rate.
Creators: name: Campbell, Gordon Alexander
Publisher: name: University of British Columbia
Year: 2011

description: Total nitrogen excretion levels were measured on five male, and three female Vancouver Island Black-tailed deer (Odo- coileus hemionus columbjanus), which, were raised in captivity in the deer unit at the University of British Columbia. They were raised from approximately three weeks of age until they had reached an adult body weight. The measurements were made at various intervals throughout the prepubertal growth period of the deer. Metabolic rate determinations were made on one of the deer, namely the doe R-5, after it had reached an adult body weight. Nitrogen balance tests were made at the same time. The method used in the nitrogen balance trials consisted of alternate periods of fasting and feeding. The ration used is described in Appendix I. It was given at one and two pound levels alternately. The procedure of fasting and feeding at different levels permitted the determination of the point of nitrogen balance, as well as that of total nitrogen excretion while feeding. The results and discussion of the nitrogen balance trials, and the distribution of nitrogen obtained, appear first, followed by that of the nitrogen excretion results observed during growth. The point of nitrogen balance was found to occur at 16.5 to 17-3 grams of nitrogen intake per day. The crude protein requirement, calculated on this basis, was approximately 100 grams for a protein of perfect biological value. The energy requirement of B-5 was found to be 1,300 to 1,400 Calories per day for maintenance. This energy requirement was met by the U.B.C. ration number 36-57 (Appendix I.) at the one pound level. This level also provided more than adequate amounts of nitrogen to fulfill the above protein requirement. The dietary requirement for nitrogen, based on the lowest level of nitrogen excretion obtained, was much lower than that calculated from the point of nitrogen balance. The lowest level obtained approximated the estimated endogenous total urinary nitrogen excretion level for an animal of the same body weight. It was concluded that insufficient time was allowed for nitrogen depletion, and that the true endogenous level was not obtained. The urea nitrogen expressed as a percentage of the total nitrogen excretion reflected the status of protein nutrition. Upon fasting the percentage fell rapidly from the non-fasting level of 90 per cent to levels of less than 85 per cent. A level of less than 75 per cent was obtained in one case. When the animal was given feed the percentage immediately returned to levels of 90 per cent or more. The prompt response on the part of urea to changes in protein intake indicated that the percentage of total nitrogen made up of urea nitrogen might be of value as an index of protein nutritional status for field studies. The creatinine nitrogen excretion level also reflected, to a slight degree, the changes in nitrogen intake. Despite the ease in determining creatinine levels, the relatively greater constancy of creatinine excretion reduces the value of such determinations as indices of protein intake. The ammonia nitrogen as a per cent of the total nitrogen reacted in an inverse manner to urea, and could be regarded as a check on the conclusions derived from the results with urea. The pattern of nitrogen excretion during growth showed changes which were similar to those observed by previous investigators on the character of increase in body weight during growth. The rate of increase in total nitrogen excretion is characterized by changes in rate of increase which occur at similar times, and in a similar manner, to those of body weight. The total creatinine nitrogen excretion increased in a regular manner during growth, from values of less than 100 milligrams per day, to values of between 400 and 600 milligrams. This is in agreement with the results of previous investigators, who have stated that creatinine excretion reflects the size of the "active body mass" The total nitrogen excretion showed a trend toward reduced levels at approximately three months of age. This reduction coincides with a major change in the growth rate, which is associated with the appearance of puberty. The reduction may indicate increased retention of nitrogen at this time, although the same result could be caused by reduced nitrogen intake. The total nitrogen excretion during growth greatly exceeded the estimated endogenous excretion level, for all body weights, as a result of the high plane of nutrition enjoyed by the deer throughout the growing period. Because the level of total nitrogen excretion reflects the level of nitrogen intake once the maintenance and growth requirements have been surpassed, it is difficult to interpret the level of excretion obtained in terms of metabolic functions. The pattern of nitrogen excretion during growth was therefore considered solely from the point of view of representing the increase in protein stores, and in the total amount of protein metabolism associated with increasing body size. The importance of these results in terms of field studies is discussed. The lack of adequate techniques, at the present time, to enable samples to be taken from the field for the type of analyses used in this experiment, makes the application of nutritional principles, such as the type discussed in this experiment, very difficult. However the results of experiments performed in the laboratory may be seen from the results of this experiment to be of great value in attempting to understand the relationship between the game animal and it environment.