Breed differences in circulating equine relaxin.

The research was focused on investigating equine relaxin — a hormone released in pregnant horses. The study analyzed hormonal patterns across various horse breeds to find any significant differences and also looked into the potential for using relaxin as an indicator of pregnancy health.

Objective and Process of the Study

• The goal of the study was to investigate the gestational pattern of relaxin production in different breeds of horses and asses. It aimed to define the normal pregnancy pattern of this hormone on a larger scale than previous studies and also to identify if all breeds had comparable patterns.
• To achieve this, the researchers collected plasma samples from a variety of equine species at different points in their pregnancies — 24 Standardbred mares had samples taken weekly, 10 pony mares were tested every 7-10 days, and 16 burros had daily samples taken during the later stages of their pregnancies.

Main Findings

• Standardbred mares exhibited higher relaxin concentrations than Thoroughbreds throughout most of their pregnancies and did not show the same midpregnancy dip in hormone level that the latter group did. Their relaxin levels declined from Day 150 until delivery.
• Pony mares had lower relaxin concentrations continuously rising throughout their pregnancies, whereas burros showed relaxin concentrations intermediate to ponies and other mares in late gestation.
• Burros induced to give birth using oxytocin experienced a sharp increase in relaxin concentrations.
• The offspring’s sex did not appear to have any effect on relaxin profiles within Standardbred mares.

Implications

• Three Standardbred mares with unusually terminated pregnancies were noted with consistently low relaxin concentrations prior to pregnancy termination, suggesting relaxin as a potential indicator of placental functioning and, therefore, pregnancy health.
• Overall, the study provides valuable information on equine pregnancy hormone patterns, which can be used to better manage pregnant horses and assess potential risks accurately.