The copper (Cu) status of grazing Romney sheep was monitored following treatment with zinc oxide (ZnO). In a series of experiments sheep of various ages were treated with ZnO as either an oral drench weekly for one year, or as an intraruminal controlled release bolus (Time CapsuleTM , AgResearch) once (on day 0) or twice (on day 0 and 40), in two consecutive years. Measurements of Cu status included Cu concentrations in liver, kidney and muscle in all animals, and liver metallothionein (MT) in sheep dosed with ZnO orally. Drenching of two-year old wethers with 12 g ZnO/week for 52 weeks did not significantly change Cu liver concentration compared to untreated control animals (mean ± SD, 1.93 ± 0.88 and 1.67 ± 0.87mmol cu/kg FW, respectively). However, administering a single 42-day intraruminal ZnO bolus to six-month old lambs resulted in decreased liver Cu concentrations after 40 days (0.96 ± 0.06 compared to 1.33 ± 0.07 mmol Cu/kg FW in controls; P<0.001). When lambs which were growing at 100g/day were treated with a second ZnO bolus and evaluated after an additional 40 days, Cu liver concentrations were reduced by a further 20% but this change was not statistically significant (P=0.07). The variable effects of different forms of Zn treatment on liver Cu concentration are discussed in terms of duration of the dose, age of the animals, DM intake, initial Cu pool size in the liver, and Cu/Zn-binding MT. Under most conditions the benefits of ZnO as an effective facial eczema control are likely to outweigh any short term reduction in liver Cu.
Proceedings of the New Zealand Society of Animal Production, Volume 58, , 199-201, 1998
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