Effect of transportation on the estrous cycle and concentrations of hormones in mares.

This research investigates how long-distance transportation affects mares’ estrous cycles and hormone levels, but found no significant changes in ovulation, estrous behavior, cycle duration, or pregnancy rates. However, transportation did cause higher cortisol and ascorbic acid levels during the journey, and notably larger increases in luteinizing hormone post-transport.

Study Design and Methodology

• 15 mares were transported for 792 km (12 hours) during their preovulatory phase of estrus, the period in the estrous cycle where the female is most receptive to mating.
• Blood samples were collected at different times before, during, and after the journey, up to 72 hours post-transportation. Additional samples were taken up to 20 days after ovulation to measure the level of progesterone, a hormone involved in maintaining pregnancy.
• Another 15 mares that were not transported (control group) also had blood samples taken at the same intervals as the transported group.

Findings

• No significant differences were found in the number of mares that ovulated, exhibited estrous behavior, had changes in the duration of the estrous cycle, or became pregnant between the transported and control groups.
• However, cortisol, a hormone associated with stress, was significantly elevated in the transported mares during mid-trip and immediately post-transportation compared to the control group.
• Similarly, ascorbic acid or Vitamin C (a component related to stress response as well) levels in transported mares increased mid-trip, but then decreased below baseline levels 24 hours after the journey.
• The study also observed increases in luteinizing hormone (LH) and estradiol (a form of estrogen), which may be naturally occurring preovulatory surges. Nevertheless, the rise in LH levels was significantly higher in transported mares immediately after transport.

Conclusions and Implications

• The study demonstrates that while transportation may not affect mares’ estrous cycles, ovulation, behaviors, and pregnancy rates, it can cause significant increases in stress-related hormones such as cortisol and ascorbic acid.
• Moreover, despite the natural increase of luteinizing hormone and estradiol during the preovulatory phase, the further rise in LH post-transportation implies a potential effect of stress on hormonal balance which may affect reproductive activities.