The effect of diet-induced obesity and pasture on blood pressure and serum cortisol in Standardbred mares.
Authors: Nostell Katarina, Lindåse Sanna, Winqvist Ellen, Bröjer Johan
Journal: Equine veterinary journal
Summary
# Editorial Summary Obesity in horses is known to disrupt metabolic and cardiovascular function, but the relative contributions of weight gain versus dietary composition to conditions like hypertension and cortisol dysregulation remain unclear. Researchers fed nine Standardbred mares a low-NSC haylage diet at 2.5 times maintenance energy for 22 weeks to induce obesity (all reached BCS >7), then monitored mean arterial blood pressure (MAP), insulin sensitivity via euglycemic hyperinsulinaemic clamp, and serum cortisol before, during, and after a four-week pasture period. Diet-induced weight gain produced a marked 18% increase in MAP (78 to 92 mmHg), elevated serum cortisol by 40% (80 to 112 nmol/L), yet paradoxically did not impair insulin sensitivity; notably, pasture turnout improved insulin sensitivity substantially (SICLAMP rose from 0.9 to 1.6) but failed to normalise either blood pressure or cortisol concentrations. These findings suggest hypertension and cortisol elevation in obese horses operate through pathways independent of classical insulin resistance, indicating that weight loss alone may be insufficient to resolve cardiovascular dysfunction without additional metabolic interventions. Practitioners should recognise that obese horses may present with vascular and endocrine complications even when insulin sensitivity appears preserved, and that pasture access—whilst metabolically beneficial—does not automatically reverse all obesity-related pathology.
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Practical Takeaways
- •Obese horses develop elevated blood pressure and cortisol levels that persist even after pasture access, suggesting these metabolic changes may require active management strategies beyond weight loss alone
- •Pasture turnout improved insulin sensitivity in obese mares despite persistent hypertension and cortisol elevation, indicating multi-system benefits of exercise and grazing
- •Monitor blood pressure and cortisol in obese horses as independent risk factors; improvements in one parameter do not guarantee normalization of others
Key Findings
- •Mean arterial blood pressure increased significantly from 78±3 to 92±3 mmHg during 22-week weight gain period and remained elevated at 93±3 mmHg after 4 weeks of pasture
- •Serum cortisol concentrations increased from 80±9 to 112±9 nmol/L during weight gain and remained elevated during pasture period
- •Insulin sensitivity (SICLAMP) was unaffected by diet-induced obesity (0.9±0.1 vs 1.0±0.1) but improved significantly after pasture access (1.6±0.1)
- •Obesity-associated hypertension and elevated cortisol were independent of insulin sensitivity changes