Utilization of hormonal profiles as indicators of reproductive capacity in beef heifers

Author

Patricia K. Hillyer

Date of Award

12-1992

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

Bert H. Erickson

Committee Members

J.D. Godkin, J.D. Smalling

Abstract

Two studies were conducted to examine the extent to which prepuberal hormone secretion can be used as an indicator of reproductive capacity in the beef heifer. The first involved prepuberal hormonal differences in 3 breeds of heifers (Angus, Crossbreds (SPxAN and HPxAN) and Polled Herefords). Basal and GnRH stimulated blood samples were obtained from Angus (AN, n=29), Crossbred (XB, n=14) and

Polled Hereford (HP, n=14) at 6 ages (3, 5, 7, 9, 11 and 12 mo) . Basal values resulted from the avg of 3 hourly bleedings; GnRH values resulted from the avg of bleeding effected 1.5 & 3 hours after GnRH. RIA's were conducted for luteinizing hormone (LH, ng/ml), follicle stimulating hormone (FSH, ng/ml), progesterone (P₄, pg/ml), androstenedione (δ₄A, pg/ml), testosterone (T, pg/ml) and estradiol (E₂, pg/ml).

Polled Herefords were distinctive in having the highest levels of the gonadotrophins, the least amount of E₂, and a longer time to reach puberty. Crossbreds were significantly heavier at all ages and highest in their basal & GnRH stimulated secretion of T (at all ages) and δ₄A (9, 11 & 12 mo) . Angus showed a higher secretion of basal & GnRH stimulated secretion of δ₄A at 3, 5 & 7 mo.

Ovulation (P₄ > 1 ng/ml) was observed in XB at 9 mo, AN at 11 mo and only 1 HP expressed high P₄ values by 12 mo of age. Groups of heifers that ovulated at an early age had higher basal & GnRH simulated secretion of E₂ & δ₄A at 3 & 9 mo respectively.

The second study was conducted over 2 years to examine the relationship between δ₄A and gonadal steroids and their correlation with number of ovarian follicles. Ovaries were removed from 16 mo old AN heifers (n=20) for Year-1 and 14 mo old ANG (n=10) and XB heifers (n=8) for Year-2. Follicles were enumerated, classified and correlated with basal and GnRH stimulated steroid concentrations in serum. Heifers were bled at 3, 5, 7, 9, 11 & 12 mo of age. Heifers with the highest number of primary follicles had significantly higher δ₄A at 9 & 11 mo and higher testosterone at 7 mo. Primary follicle numbers were positively correlated with secondary, growing, atretic and total vesicular follicles (r=.5).

These results suggest: 1) that δ₄A, T and E, could be used to predict early age at puberty and 2) that basal and GnRH stimulated δ₄A and T either before or around the time of weaning could be used to predict primary follicle numbers. Utilizing these results, prepuberal androgens in conjunction with E₂ could be used to predict the potential reproductive capacity of the beef heifer.

Recommended Citation

Hillyer, Patricia K., "Utilization of hormonal profiles as indicators of reproductive capacity in beef heifers. " Master's Thesis, University of Tennessee, 1992.
https://trace.tennessee.edu/utk_gradthes/6996