Gonadotrophin profiles and dioestrous pulsatile release patterns in mares as determined by collection of jugular blood at 4 h intervals throughout an oestrous cycle.

This research paper examines the variable nature of the Follicle Stimulating Hormone (FSH) profiles in mares during the dioestrus phase of the oestrous cycle. It makes use of extensive blood sampling to determine more accurately the pattern of this hormone, and the related Luteinizing Hormone (LH), over the course of the cycle. The findings suggest that once-a-day sampling methods can lead to misleading determinations of FSH profiles.

Research Methodology

• The research was conducted on six mares, where their blood was sampled from the jugular vein at 4-hour intervals throughout an ovulatory cycle.
• The objective was to account for the pulsatory nature of plasma FSH and LH, which is difficult to capture with less frequent sampling methods.
• The frequency of gonadotrophin pulses during dioestrus was also measured.

Key Findings

• The research identified regular synchronous pulses of FSH and LH in all mares between day 4 and day 12 of the cycle.
• The LH pulse amplitude decreased significantly between day 4 and day 10, while the FSH pulse amplitude stayed largely stable with only a minor, non-significant dip on day 6.
• Simulating a once-a-day sampling by selecting samples collected at 08:00 h or noon resulted in significantly different patterns, highlighting the issue with once-a-day sampling methods.
• LH was found to be higher during the periovulatory surge than during dioestrus, whether daily means or selected samples were used.

Conclusion and Implications

• The research concludes that once-a-day sampling provides misleading data for determining FSH profiles due to the marked pulsatility of plasma FSH during dioestrus.
• The pattern of large, slow FSH pulses was found to be consistent among mares, different from what is captured by the daily mean FSH profiles.
• No discrete “surges” in FSH were observed during dioestrus, but the amplitude of the FSH pulse tended to fluctuate between increase and decrease.
• The research also suggests that these higher-amplitude FSH pulses, which precede ovulation by approximately 10 days, could potentially signal follicular recruitment in mares.

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Researcher Affiliations

• Animal and Veterinary Sciences Group, Lincoln University, Canterbury, New Zealand.