The effect of zinc oxide and elemental zinc boluses on the concentrations of Zn in serum and faeces, and on providing protection from natural Pithomyces chartarum challenge in sheep

The effect of zinc oxide and elemental zinc boluses on the concentrations of Zn in serum and faeces, and on providing protection from natural Pithomyces chartarum challenge in sheep
Peer reviewed

Abstract

AIM: To investigate the effi cacy of intra-ruminal Zn boluses as aids in providing protection from natural Pithomyces chartarum challenge in sheep.
METHODS: Seventy-two adult sheep (mean weight 59 (SEM 0.5) kg) were divided into four groups. Commencing on Day 0, they received either a proprietary bolus containing 67 g ZnO (equivalent to 54 g Zn) (ZnO group), two different levels of elemental Zn (81 and 108 g) delivered in boluses each containing 27 g Zn (Zn81 and Zn108 groups, respectively), or remained untreated (control). Concentrations of Zn in serum, activities of gamma-glutamyl transferase (GGT) in serum, and spore counts on pasture were measured weekly from Day −6, and concentrations of Zn in faeces weekly from Day 21, until Day 77.
RESULTS: Mean concentrations of Zn in serum between Days 14 and 42 were significantly higher in ZnO animals (15.4 (SEM 0.70) µmol/L) than the other groups. Mean concentrations in Zn108 animals (11.1 (SEM 0.26) µmol/L) were significantly higher than controls, but there were no differences between Zn81 and the controls (9.9 (SEM 0.20) and 9.4 (SEM 0.26) µmol/L, respectively). Between Days 21 and 49, there was no significant difference in mean concentrations of Zn in faeces between ZnO and Zn81 animals (307 (SEM 28) and 281 (SEM 29) mg/kg fresh weight (FW), respectively), but concentrations were significantly higher in Zn108 animals (500 (SEM 40) mg/kg FW). Spore counts exceeded 70,000/g on Days 14, 28, 49, 56 and 63 but there were no clinical signs of facial eczema. In controls, activities of GGT were unchanged until Day 21, then increased to 637 IU/L at Day 70; for ZnO animals, activities remained <75 IU/L until Day 14, then increased to 200 IU/L at Day 70; for Zn81 and Zn108, they remained <75 IU/L until Day 35, and then increased at Day 70 to 369 IU/L and 293 IU/L, respectively. From Day 56 activities were significantly lower in all treated groups compared with controls, but there was no significant difference between the three Zn bolus treatments. There were significant negative correlations between activities of GGT and concentrations of Zn in serum in Zn108 animals, and with concentrations of Zn in faeces for both Zn81 and Zn108 groups.
CONCLUSION: Elemental Zn boluses can reduce activities of GGT associated with elevated spore counts. The association between concentrations of Zn in faeces and activities of GGT suggests that a minimum concentration of Zn in the gastrointestinal tract may be important in providing protection against sporidesmin.
KEY WORDS: Facial eczema, zinc, sheep, intra-ruminal device, bolus, sporidesmin


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