Copper is an essential trace element required for animal health. In deer, like other species of farmed livestock, copper is critical in the formation of the collagen matrix that keeps bones strong. This is why animals that experience copper deficiency early in life can have bones that are weak and prone to fractures and deformities.
Copper is involved in the formation of red and white blood cells and the synthesis and release of life-sustaining proteins and enzymes. White blood cells play a pivotal role in the immune system, potentially making copper-deficient animals more susceptible to infectious diseases. Copper deficiency also causes defects in the insulating layer of nerves, leading to the weakness and wobbly gait associated with swayback in deer.
Copper levels fall over the winter, meaning that adequate copper levels in the autumn are no guarantee that they will be sustained until spring. Testing in the late winter to early spring will assess the copper levels of the deer when at their lowest. This will give an opportunity to make decisions over the need for supplementation prior to late pregnancy and, in the case of breeding hinds, leading into fawning.
Similarly, copper levels will be at their seasonal highest in deer in the late summer. Therefore, testing then allows an assessment for the need for supplementation at weaning if carried out pre-roar.
The only truly reliable assessment of copper levels is by liver sampling, either by collection at slaughter premises or through biopsy from live animals. The reason for this is that copper is stored in the liver, from where it is released into the blood. Blood copper levels are maintained at adequate levels until the liver reserves are depleted. Therefore, sampling the liver for copper is important for assessing the reserves to cover a period of low availability or high animal demand.
Our veterinarians are comfortable collecting liver biopsy samples from sedated deer, as demonstrated in a practice-wide survey of liver copper levels in deer through July-October. 187 liver samples were collected from deer on 21 farms covering Central Otago, Twizel, South Canterbury, and Nelson-Marlborough. Of the 187 samples, 86 (46%) had copper levels less than the 100umol/kg level deemed to be marginal and potentially deficient, with many much lower than 100.
These samples were collected from either rising-one-year-old (R1) deer or pregnant rising-two-year-old (R2) or mixed-age (MA) hinds. The R1 deer were on the verge of kicking off their spring growth surge (if not already into it) and the R2 and MA hinds were approaching late pregnancy and supporting the requirements of a rapidly developing foetus.
Testing is the basis for making decisions on the need for copper supplementation. In fact, the repeat liver sampling of ‘sentinel’ animals, to evaluate copper levels with or without supplementation, is easily implemented for farm-specific information. For example, we have a farm where testing of pregnant hinds at the end of winter revealed low copper levels. Supplementation with a copper bullet was undertaken, and then sampling repeated 8 weeks later to assess the effect of this. It showed a very satisfactory elevation of liver copper reserves. These sentinel deer will be re-sampled prior to weaning in March to see to what point their levels have reached, and a decision will then be made on the potential need for supplementation going into mating.
If testing shows that the copper status of some individuals at certain times of the year is deficient or marginal, decisions on supplementation may need to be made on the grounds of insurance. In these situations, copper supplementation will raise the copper status of the herd and remove animals ‘at risk’ of clinical deficiency or sub-optimal productivity.
Although there is a lack of hard data to show productivity responses to copper supplementation of deer, in the absence of clinical signs of deficiency it is important to think of the critical role copper plays within the body. With the growth potential of modern farmed deer, both skeletally and muscular, along with velvet, first principles would indicate that maintaining copper adequacy through sufficient liver reserves in times of low availability and high demand is good insurance.
