Masters Theses

Date of Award

8-1994

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

Bert H. Erickson

Committee Members

J.D. Smalling, W.R. Backus, J.C. Waller

Abstract

To examine the extent to which gonadotrophin concentration in peripheral blood is correlated with follicular numbers and body weight [birth, weaning (ADJ205) and yearling], prepuberal Angus (n=30) and Crossbreds (n=22) heifers were evaluated at 5, 7, 9, 11 and 14 mo of age. Basal and GnRH-stimulated gonadotrophin secretion was determined from the average of two bleedings effected at 1.5 hour intervals. Gonadotrophins (LH & FSH) were quantified by RIA. All heifers were synchronized and in luteal phase when ovariectomized at 16 mo of age. Ovaries were sectioned and stained for light microscopy.

GnRH-stimulated gonadotrophin secretion changed with age. The FSH response increased significantly between 5 and 9 mo (p < 0.01) and then decreased at 14 mo (p < 0.01). LH release increased with age and concentrations were lower at 5, 7 and 9 mo than at 11 and 14 mo (p < 0.01) . Basal concentrations of FSH and LH did not change between 5 and 14 mo (p > 0.10) . However, FSH did show a downward trend as age increased.

Basal and-GnRH stimulated concentrations of FSH were not associated with follicular numbers (p > 0.10). However, when heifers were partitioned according to their gonadotrophin concentrations (low, medium or high) , associations between normal vesicular, atretic vesicular and total vesicular follicles and concentration of FSH were significant at 14 mo for basal and 7 mo for GnRH-stimulated secretion. Groups varying in FSH concentration were not different in follicular numbers at any age (p > 0.10). In contrast, basal and GnRH-stimulated LH groups were significantly different in number of primary follicles at 14 mo (p < 0.06). Additionally, basal LH was positively related to number of primary and secondary in the low (r= .68, p < 0.03) and high groups (r= .56, p = 0.08), and number of secondary follicles was negatively correlated with GnRH stimulated LH secretion in the high group (r= -.64, p < 0.05) .

Body weight was inversely related to basal FSH concentration at 9, 11 and 14 mo and GnRH-stimulated secretion at 5, 7 and 9 mo. In contrast, GnRH-stimulated LH was positively associated with weaning and yearling weight at all ages except 9 and 14 mo, but basal LH was not associated with body weight (p > 0.10). Basal and GnRH-stimulated FSH groups were not different in body weight at any age (p > 0.10) . With LH, however, the high responders to GnRH at 5, 11 and 14 mo were heavier as yearlings (p < 0.10).

The results suggest that the combination of yearling weight and basal and GnRH-stimulated concentrations of gonadotrophins in peripheral blood could be useful indicators of number of follicles and this combination might be useful in identifying heifers of superior reproductive potential.

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