Aspects of copper metabolism in deer : with reference to requirements for and response to supplementation

Abstract

A survey of 3661 farmed deer killed in the South Island revealed that 46% contained liver Cu concentrations less than 20 mg/kg DM, the likely threshold concentration below which deficiency may be expected. Mean liver Cu concentrations of 457 killed feral animals were more than 3 fold higher than the mean and 5 fold higher than the median of liver Cu concentrations of farmed deer (35 and 25 mg/kg DM, respectively). Investigation of a possible relationship between liver Cu concentration and soil type upon which the animals grazed revealed that the more weathered the soil type e.g. podzols, the lower were associated liver Cu concentrations of deer grazed thereon.

To investigate a possible reason for this generally low Cu status of farmed deer, a series of 3 experiments examined liver Cu changes subsequent to injection of Cu-EDTA. The results of an initial experiment indicated that translocation of Cu from the injection site occurred within 7 days, thus a liver sample obtained 7 days post-injection would represent maximum response in liver Cu concentration to injection.

In a second experiment (B), liver Cu concentrations of both sheep and deer were significantly increased subsequent to each of 2 injections of Cu-EDTA, this increase was proportional to the size of dose. Large decreases were evident in all treatment groups of both species 4 weeks after the second injection. Rates of loss of hepatic Cu (Y, mg/day) as a function of liver Cu concentration (X, mg/kg) were described by the equations: Deer: Y = 0.000016X² + 0.00512X - 0.537 (r² = 82.8 %; P < 0.01) Sheep: Y = 0.000003X² - 0.000048X - 0.223 (r² = 71.1 %; P < 0.01). These results suggested that deer may be more prone to low Cu status, due to higher apparent rate of excretion of Cu from the liver, than sheep.

A further experiment (C) investigated the reported differences in Cu availability of different diets and their possible effect on depletion rates of deer subsequent to injection of Cu-EDTA. Mean liver Cu concentrations of deer offered silage, a diet notoriously low in available Cu, decreased during a 20 day pre-injection period, while those of deer offered a pelleted concentrate diet (of similar Cu concentration) increased. Rates of loss of hepatic Cu subsequent to injection, as a function of liver Cu concentration were not significantly different between diets or to that described in experiment B, demonstrating the importance of animal Cu status on depletion rate. This highlighted the difficulties in estimating dietary Cu availability, the calculation of which, being dependent on changes in liver Cu concentration, is therefore influenced by Cu status of the animal.

Many aspects of Cu metabolism have been successfully elucidated in sheep, published data thereby making them a model for comparison. In particular, Suttle (1974) has developed an oral vs intravenous repletion technique which effectively estimated dietary Cu availability to sheep. Attempts to utilize this method to estimate availability of dietary Cu to deer had to be abandoned due to animal welfare considerations when feed intake was compromised by stress.

A further 2 experiments investigated the response of deer to either oral (CuO needles) or parenteral (Cu-EDTA) supplementation. In experiment D, liver Cu concentrations of animals receiving either form remained elevated for approximately 6 months after administration, while unsupplemented deer had levels which remained below 20 mg/kg DM. Animals given CuO grew significantly faster (up to 20 %) than either control or Cu-injected animals.

In experiment E, Cu status of unsupplemented mature, yearling and weaner stags declined to below 20 mg/kg liver during late autumn to spring, subsequently increasing during summer. Supplementation with CuO resulted in elevations in liver Cu concentration for at least 6 months in mature and yearling stags and for 4 to 6 months in weaner stags. There was a significant growth advantage of supplemented vs unsupplemented yearling stags, but no significant differences were observed between treatment groups of mature or weaner stags. Toxicity was not evident at high doses (up to 80 g) of CuO.