Liveweight gain and copper status of young deer treated or untreated with copper oxide wire particles on ten deer farms in Canterbury

AIMS: To measure the liveweight response of young deer to copper supplementation on a range of deer farms in the Canterbury region of the South Island, New Zealand, and relate any response to plasma copper concentration. METHODS: On each of 10 farms throughout north and mid-Canterbury, young deer (4-7 months old) were allocated by liveweight to two groups of 45-50. The deer in one group each received 5 g copper oxide wire particles (COWP) at the start of the project (March-June 2000) and a further 10 g COWP 3 months later (+Cu group), while the other group received no copper supplementation (-Cu group). Liveweight (+/-1 kg) of all deer was recorded monthly. A 10 ml blood sample was taken from a sub-sample of 10 animals in each group at the beginning of the trial and from the same animals 3 and 6 months later for measurement of plasma copper concentration. RESULTS: There was no significant effect (p=0.96) of treatment with COWP on liveweight gain (overall mean liveweight gain = 169 g/day). This result was consistent for all farms and for both periods. Mean plasma copper concentration declined from 12.5 (SD 3.4) to 10.3 (SD 3.0) micromol/l in +Cu groups, and to a significantly lower level (p<0.001) of 8.6 (SD 3.2) in -Cu groups after 3 months, at which time 38% of -Cu animals were considered hypocupraemic (<8 micromol/l). At the end of the second 3-month period there was no significant treatment effect on plasma copper concentration, which averaged 9.4 (SD 2.3) micromol/l. Of the feed samples submitted (n=46), only 17% had a copper concentration <5.0 mg/kg dry matter (DM), 13% had a molybdenum concentration >1.0 mg/kg, and 21% had a sulphur content >3.5 g/kg. CONCLUSIONS: Under the conditions of these trials, no response in liveweight gain to copper supplementation was observed despite evidence of hypocupraemia in 38% of -Cu animals, which gained weight at similar rates to those that had adequate plasma copper levels. The extent of the hypocupraemia was either not sufficiently severe, or not maintained for a long enough period to cause copper deficiency resulting in reduced liveweight gain. No other signs of copper deficiency were evident. There is scope for deer farmers to reassess the need for copper supplementation in young deer.