Masters Theses

Date of Award

6-1986

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

Bert H. Erickson

Committee Members

H. G. Kattesh, T. T. Chen

Abstract

Reproductive efficiency is a major concern in the production of livestock. In an effort to determine if predictive criteria for reproductive performance could be developed in the prepuberal female bovine, heifers were used to establish and compare prepuberal LH and FSH secretion profiles and evaluate the hypothalamic response to an E2 (17β-estradiol) challenge. This information was then related to reproductive performance through the first calving. Blood samples were collected at various prepuberal ages to establish profiles of LH and FSH secretion. The E2 challenge was effected by injecting 1 mg of Eg2-benzoate intramuscularly and collect-ing blood samples at 8, 11 and 14 hours after injection. Radioimmunoassays (RIAs) were developed to measure plasma levels of LH and FSH. Ages studied ranged from 5 to 424 days. A significant difference (P>0.01) in levels could be seen between the pre- (31±14 days) and post- (387±±22 days) weaning periods. Mean FSH level for the age-range studied was 12±5.6 ng/ml with a range of 3.8 to 39.7 ng/ml. LH averaged 388±271 pg/ml with a range of 135 to 3148 pg/ml and was significantly higher (P>0.01) during the post-weaning period (387±22 days). A comparison of the hormonal profiles of the heifers with the highest and lowest levels of FSH and LH secretion during the first 100 days after birth revealed that the FSH levels of the respective groups were significantly different (P<0.01) but the LH levels were not (P>0.10). The effect of E2 on LH secretion was significant (P<0.01) but it was not for FSH secretion. Ages tested ranged from 117 to 193 days. Of the 38 animals tested, 20 did not respond, 16 responded positively (any level 2 or more times greater than the 8 hr sample but less than 10 ng/ml) and 2 responded with a preovulatory-like LH surge (LH peaks ≥10 ng/ml, Schillo et al., 1983). The number of responders was evenly distributed throughout all of the ages tested. Responses of higher magnitude occurred between the ages of 162 to 193 days. Although the FSH response was not signifi-cant, 4 of the 38 animals responded positively to the E2 challenge. The responses occurred between 162 and 193 days of age. Of the 41 heifers used to relate prepuberal LH and FSH secretion to reproductive performance, 19 calved within one estrous cycle of one another, 2 were open and 20 were exposed to an infertile bull which made them ineligible for further study. Due to the low number of animals studied, no significant differences (P>0.10) between the heifers that calved and those open were observed in either the profile of LH or FSH secretion. Although not statistically significant, FSH concentration was higher in the heifers that calved. Comparing the prepuberal E2 challenge to reproductive performance showed that the heifers that calved had a higher LH response. This difference was not significant compared to the open heifers, which was probably due to an insufficient number of animals. The results suggest that prepuberal FSH concentrations are higher in heifers that calve. Fertile heifers also respond to the Eg challenge with higher levels of LH. Further study is needed to validate the results, but at this point there seems to be potential for developing predictive criteria, based on prepuberal gonadotrophin levels, for reproductive performance.

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