Evaluation of increasing dietary zinc on copper metabolism and in the prevention of cumulative cooper poisoning in sheep

Author(s)

Antonio Humberto Hamad Minervino

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina Veterinária e Zootecnia (FMVZ/SBD)
• Defense date: 2011-02-25

Examining board members

Enrico Lippi Ortolani; Alexandre Coutinho Antonelli; Raimundo Alves Barreto Junior; Fernando José Benesi; Viviani Gomes

• Advisor: Enrico Lippi Ortolani

Abstract

The objective of this study was to evaluate the effects of increasing quantities of dietary zinc on the metabolism of copper and the prevention of copper toxicosis in sheep. Forty male, mixed breed St. Inês, sheep were divided into 5 experimental groups, each containing 8 animais, and were submitled to different doses of copper (Cu) and zinc (Zn). Animais from Groups A, B, C, and D received 12 mg of Cu per kg of body weight daily (BW). Additionally, those in Group A, B, and C were supplemented with increasing levels of zinc: Group A, 1 mg of Znl kg BW; Group B 4 mg of Znl kg BW; and Group C 8 mg of Zn/kg BW. Group H animais served as controls and received only the basic diet. The experiment occurred during 14 weeks during which hepatic biopsies were done at the beginning of the study, and tissue fragments were collected at the end of the experiment after the animais were euthanized. The concentrations of Zn, Cu, bile, and whole blood were determined. Weekly blood samples were obtained to evaluate biochemical and hematological parameters during which the weight of each animal was recorded. Animais used as controls (Group H) and those that supplemented with elevated doses of Zn (Group C) did not demonstrate clinical manifestation of intoxication. However, one member from Group A, B, and D demonstrated clinical manifestations that were consistent with accumulative copper toxicosis (ACC). Elevated values of hepatic Cu occurred in ali groups between the beginning and the end of the experiment, but this elevation was drastically more reduced in Group H animais due to comparatively reduced Cu levels within the basic diet. At the end of the experiment it was verified that Group A, B, C, and D animais demonstrated more elevated concentrations of hepatic Cu relative to their counterparts from Group H. Members from Group C (elevated Zn) demonstrated reduced concentrations of hepatic copper relative to those from Group D, who did not receive any zinco Members from groups that received Zn supplement demonstrated more elevated concentrations of hepatic metallothionein (MT) relative to those from Groups D and H that did not receive any supplementation. Members from Groups A and D demonstrated more reduced values of Cu bound to MT (Cu-MT), relative to those from Groups D and H. Consequently, there was a greater proportion of Cu- MT relative to total Cu in animais from Groups A and C when compared with those from Group D. Significant differences in the values of yGT activity were not verified between the groups that were supplemented with Cu; there was only a distinct difference between members of the control group and the other groups. There was an elevation in the values of yGT activity relative to time 0 on Groups A, B, C and D effective from the eight week. An increase in the values of AST activity relative to time 0 was observed in animais from groups that were supplemented, this being effective from the tenth week of the experiment. Alterations to biochemical and hematological variables were not observed during the experiment; occurring only in those three animais that demonstrated clinical manifestations of ACC. The amount of copper used to challenge the sheep was adequate to induce a substantial increase of hepatic copper and produce the characteristic manifestations of copper toxicosis in some animais. The addition of elevated values of Zn prevented the death of animais during the experiment; promoted a reduction in the quantity of copper accumulated within the liver; stimulated the synthesis of metallothionein; incremented the quantity and the percentage of hepatic copper bound to metallothionein. These conditions favor the prevention of cupper toxicosis in sheep. (AU)

• FAPESP's process: 07/00733-7 - Evaluation of increasing dietary zinc on copper metabolism and on prevention of cumulative copper poisoning in sheep
• Grantee: Antonio Humberto Hamad Minervino
• Support Opportunities: Scholarships in Brazil - Doctorate