Title page for ETD etd-04042008-101908


Type of Document Master's Thesis
Author Tanner, Genevieve Elizabeth
Author's Email Address mlum@agcenter.lsu.edu
URN etd-04042008-101908
Title The Influence Of Calf Selenium Status On Gpx-1 And 3 Activity And Liver Gpx-1 mRNA
Degree Master of Science (M.S.)
Department Animal Science (Animal, Dairy, & Poultry Sciences)
Advisory Committee
Advisor Name Title
Jason E. Rowntree Committee Chair
Cathleen Williams Committee Member
Kenneth Bondioli Committee Member
Lee Southern Committee Member
Keywords
  • Selenium
  • GPX
  • mRNA
  • calf
Date of Defense 2008-03-28
Availability unrestricted
Abstract
The purpose of this research was to determine the influence of dietary Se on glutathione peroxidase (GPx)-1 and 3 activities and relative liver GPx mRNA levels in growing Holstein bull calves. Calves (n = 14) were started 28 d after birth on either a Se adequate (0.15 ppm Se) or deficient (0.01 ppm Se) diet consisting of 3 growth phases and maintained on the diet until 180 d of age. Blood samples were taken from each calf for determination of GPx-1 and GPx-3 activity. Three calves were euthanized at d 21 of age for determination of baseline liver GPx-1 mRNA level. Four calves from each treatment were euthanized at d 180 of age for determination of liver GPx-1 relative mRNA level. Feed intake and average daily gain were not affected by Se level. Mean liver Se concentration was higher (P < 0.05) for baseline calves and those fed the Se adequate diet than for calves fed the Se-deficient diet, but there was no difference between baseline calves and Se adequate calves with respect to liver Se concentration. The GPx-1 activity was greater for Se adequate than Se-deficient calves (P < 0.01) but not until d 84 of age. The GPx-3 activity was considerably more variable than that of GPx-1 with respect to the trend observed for activity by day, and the GPx-3 activity of the Se-deficient group was only less than that of the Se adequate group (P < 0.05) on d 180. N-fold differences were calculated for relative GPx-1 mRNA levels between treatments. There was a 50% decrease in GPx-1 mRNA for Se-deficient calves (P < 0.05) compared with the Se adequate calves. Regression analysis also was performed to determine the relationship between the various response variables. There was only a moderate relationship (r2 = 0.58) between GPx-1 mRNA transcript levels and GPx-1 activity at d 180, despite a correlation coefficient of 0.76. The relationship between GPx-1 mRNA transcript level and GPx-3 activity at d 180 was much stronger (r2 = 0.81), with a correlation coefficient of 0.90, which was unexpected, as GPx-3 is generally considered a short-term indicator of Se status and therefore a much more variable response. Erythrocyte GPx-1 activity was much more sensitive to Se in the diet and thus reflected the diet more closely than did GPx-3. However, GPx-3 activity was more highly correlated to GPx-1 transcript levels. These unexpected results suggest that another trial utilizing larger sample sizes and serial sampling of liver tissue with the sampling of plasma and erythrocytes may provide a clearer picture of the relationship between liver GPx-1 mRNA , tissue Se concentration, and GPx enzyme activities in neonatal and growing Holstein calves.

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