Serum progesterone concentrations in pregnant and nonpregnant heifers and after gonadotropin releasing hormone in luteal phase heifers |
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| Authors: | Fred N Thompson Terry Clekis Terry E Kiser Hubert J Chen Charles K Smith |
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| Institution: | 1. Department of Physiology and Pharmacology, University of Georgia Athens, Georgia 30602 USA;2. Department Animal and Dairy Science, University of Georgia Athens, Georgia 30602 USA;3. Department Statistics and Computer Science, University of Georgia Athens, Georgia 30602 USA |
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| Abstract: | Serum progesterone (P4) concentrations were quantitated in 18 Holstein heifers from days 5 to 16 after estrus in an effort to ascertain the effects of pregnancy on circulating levels of this hormone. The P4 concentration rose faster between days 5 and 10 in the pregnant heifers compared to P4 levels in both the non-pregnant heifers and the killed sperm inseminated group. It was found that serum P4 levels were significantly (P<.002) elevated across the entire interval in the pregnant heifers compared to the other experimental groups. It was concluded that pregnancy had a stimulatory effect on P4 levels and that pregnancy failure is not simply due to the inability of corpora lutea to secrete sufficient P4.The administration of 250μg gonadotropin releasing hormone (GnRH) to 10 Holstein heifers on day 7 after estrus resulted in a significant (P<.025) elevation of serum luteinizing hormone concentrations from 15 min to 3 h postinjection. Similarly this treatment resulted in a significant (P<.05) elevation of serum P4 levels from .5 to 4 h post-injection. It is concluded that GnRH at this dosage has a transient effect on P4 levels in luteal phase heifers. |
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