Identifier

etd-04042008-101908

Degree

Master of Science (MS)

Department

Animal Science (Animal, Dairy, and Poultry Sciences)

Document Type

Thesis

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.

Date

2008

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Jason E. Rowntree

DOI

10.31390/gradschool_theses.3790

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