Doctoral Dissertations

Date of Award

5-1993

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Animal Science

Major Professor

B.H. Erickson

Committee Members

T.T. Chen, J.W. Oliver, J.D. Godkin, H.G. Kattesh

Abstract

Cattle that ingest tall fescue infected with the fungal endophyte, Acremonium coenophialum, exhibit signs of ergot alkaloid toxicity. Symptoms characteristic of fescue-toxicity include a reduction in weight gain, increased basal body temperature and exhibit reproductive problems including a delay in puberty, a reduced rate of conception, an increased rate of abortion, and an inhibition of pituitary prolactin secretion. A study was conducted to determine: 1) if follicular development and function were compromised in the heifer raised on endophyte-infected fescue, 2) if there were alterations in basal and stimulated pituitary and ovarian hormone secretion, and 3) if the toxins produced by the fungus endophyte (i.e. ergotamine) could affect steroid secretion by granulosal and thecal cells in culture. Results from this study indicate that prolactin secretion is inhibited and basal gonadotrophin (LH and FSH) levels tend to be elevated in the E+ fescue ingesting heifer. Luteinizing hormone release in response to 17β-estradiol secretion by the E+ yearling heifer was reduced at 14-15 hours after the E₂ injection in years 1 (P > .10), 2 (P < .05) and 3 (P > .10). Results from this study also showed that only 36% of the E+ yearling heifers had ovulated in response to E₂-stimulation compared to 71% of the controls. Similar results were observed in the 8-month-old heifer following GnRH-stimulation in which 85% of the control heifers had produced a corpus luteum compared to only 34% of the E+ heifers. Androstenedione, testosterone and estrogen secretion was inhibited in the E+ heifer. In addition, the number of primary, secondary, and antral follicles and regressed corpora lutea were reduced in E+ fescue ingesting heifers. Ergotamine, a fungal endophyte product, was shown to act directly on the granulosal and thecal cell to alter steroid production and secretion. Ergotamine stimulated androstenedione and progesterone secretion by the thecal cell; however, estrogen and progesterone production by the granulosal cells in culture was reduced. It appears, therefore, that reductions in follicular development, and alterations in gonadotrophin and steroid secretion may all contribute to the lowered reproductive efficiency seen in the fescue ingesting cow or heifer.

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