Clinical Research Abstracts of the British Equine Veterinary Association Congress 2015.
Authors: Smith S, Marr C M, Menzies-Gow N J
Journal: Equine veterinary journal
Summary
# Editorial Summary Thoroughbred foal birthweights have risen considerably in recent years, prompting investigation into whether maternal obesity and metabolic dysfunction drive this trend. Researchers monitored 57 pregnant Thoroughbred mares across gestation, collecting body condition scores, weights and fasting blood samples at 60-day intervals to measure insulin, leptin and triglyceride concentrations, then correlated these markers with foal birthweight at delivery. Whilst 55% of mares were obese (BCS ≥7), only 1.5% exhibited fasting hyperinsulinaemia and insulin showed no relationship with body condition; however, leptin concentration peaked at mid-gestation and correlated significantly with BCS, with higher leptin in early and late pregnancy paradoxically associated with lighter foals (r = -0.64). Heavier foals were born to mares with higher body condition scores, suggesting that increased maternal adiposity itself—rather than overt insulin dysregulation—may be the primary driver of elevated birthweight. For practitioners, these findings indicate that whilst most obese mares maintain normal fasting insulin levels, elevated leptin during specific gestational windows may serve as a useful biomarker for predicting foal birthweight and identifying pregnancies at potential risk of dystocia or neonatal complications. Monitoring maternal condition throughout gestation and considering nutrition management accordingly remains clinically prudent, particularly given the strong positive correlation between mare BCS and foal size.
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Practical Takeaways
- •Monitor body condition score in pregnant Thoroughbred mares, as obese mares (BCS≥7) consistently produce heavier foals, which may increase dystocia risk
- •Leptin concentration measured during early and late gestation may be a useful biomarker to predict foal birthweight and manage obstetric complications
- •Hyperinsulinaemia is not a significant finding in pregnant Thoroughbred mares, so insulin-related metabolic dysfunction may not be the primary driver of increased birthweights in this population
Key Findings
- •55% of pregnant Thoroughbred mares had body condition score ≥7, with obese mares producing significantly heavier foals (r=0.13, P<0.001)
- •Leptin concentration was significantly correlated with body condition score (r=0.29, P<0.0003) and inversely correlated with foal birthweight at 60-119 and 240-299 days gestation (r=-0.64, P<0.05)
- •Only 1.5% incidence of fasting hyperinsulinaemia was identified throughout gestation with no association between fasting insulin and body condition score
- •Serum insulin concentrations were significantly elevated in early gestation (0-119 days) compared to late gestation (180-359 days)