Effects of a non-steroidal aromatase inhibitor on ovarian function in cattle
M. Jimena Yapura A , Reuben J. Mapletoft B , Jaswant Singh A , Roger Pierson C , Jonathan Naile D , John P. Giesy A D , Hong Chang D , Eric Higley D , Markus Hecker D and Gregg P. Adams A E
+ Author Affiliations
- Author Affiliations
A Department of Veterinary Biomedical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5B4, Canada.
B Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5B4, Canada.
C Department of Obstetrics, Gynecology and Reproductive Sciences, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan S7N 0W8, Canada.
D Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan S7N 0W8, Canada.
E Corresponding author. Email: gregg.adams@usask.ca
Reproduction, Fertility and Development 24(4) 631-640 https://doi.org/10.1071/RD11239
Submitted: 20 September 2011 Accepted: 6 October 2011 Published: 25 November 2011
Abstract
Effects of the non-steroidal aromatase inhibitor letrozole on ovarian function in cattle were determined. The hypothesis that letrozole would arrest growth of the dominant follicle, resulting in emergence of a new follicular wave at a predictable post-treatment interval, was tested. Heifers were assigned randomly to four groups 4 days after follicular ablation (~2½ days after wave emergence) and given intravenous doses of 500 (n = 9), 250 (n = 10), or 125 µg kg–1 (n = 10) letrozole or phosphate-buffered saline (controls; n = 10). Blood was collected and ovarian structures were monitored daily by transrectal ultrasonography. Plasma concentrations of LH and FSH were measured by radioimmunoassay; plasma concentrations of letrozole were determined by high-performance liquid chromatography tandem mass spectrometry. A single intravenous dose of letrozole did not induce regression of the dominant follicle present at the time of treatment, nor did it directly affect FSH release. Conversely, treatment with letrozole increased endogenous concentrations of LH and extended the lifespan of the dominant follicle, which delayed the next FSH surge and subsequent follicular wave emergence. Letrozole continues to have potential as a non-steroidal treatment for controlling ovarian function in cattle.
Additional keywords: bovine reproduction, oestradiol, ovarian synchronisation.
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