The effect of mare obesity and endocrine function on foal birthweight in Thoroughbreds.

The research investigates whether obesity and endocrine dysfunction in Thoroughbred mares are connected to the recent increase in Thoroughbred foal birthweights. The researchers analyzed insulin, leptin, and triglyceride concentrations in mares throughout gestation to ascertain their relationship to obesity and foal birthweights.

Research Methods

• The study recruited a total of 66 mares, with the study beginning from 40 days post-breeding.
• Body condition score (BCS), weight, and blood samples of the mares were collected every 60 days throughout gestation.
• Each mare’s serum/plasma insulin and leptin concentrations, triglyceride levels, and the birthweight of their foals were recorded and analyzed using a linear mixed effects model.

Results

• Serum insulin levels observed were greatest between 1-60 days and 61-120 days of gestation. However, there was no significant hyperinsulinemia, and no evident correlation between insulin concentration with BCS.
• Leptin concentration peaked at 181-240 days of gestation and it strongly correlated with BCS. This might suggest that leptin plays a vital role in fat metabolism during pregnancy, leading to an increase in foal birthweight.
• Triglyceride concentrations were highest at 241-300 days of gestation. Surprisingly, no association between triglyceride level and BCS was found.
• Notably, there was a weak positive correlation between foal birthweight and BCS, indicating obese mares gave birth to heavier foals.
• Further, an inverse correlation was observed between leptin concentrations at 61-120 and 241-300 days of gestation and foal birthweight. Therefore, the decreased foal birthweight is correlated with an increase in leptin concentration during early and late gestation.

Conclusions

• The study found a correlation between mare BCS and foal birthweight. However, the researchers acknowledged that their finding might have been affected by reduction in sample size and tight clustering of BCS, which could have influenced their findings.
• The study did not identify any significant hyperinsulinemia in the mare population. Therefore, the study did not find strong evidence that insulin plays a major role in influencing foal birthweight.
• The study found a significant relationship between leptin concentration in early and late gestation and decreased foal birthweight, suggesting that leptin may play a crucial role in determining foal birthweight.
• The findings of this study warrant further research to establish whether leptin concentration in late gestation could be used to predict foal birthweight.