Effects of grazing system and season on glucose and insulin dynamics of the grazing horse
Authors: Williams C.A., Kenny L.B., Burk A.O.
Journal: Journal of Equine Veterinary Science
Summary
# Editorial Summary: Grazing System and Equine Glucose–Insulin Dynamics Rotational grazing is widely advocated for livestock management, yet evidence supporting its metabolic benefits in horses remains sparse. Williams and colleagues compared continuous versus rotational grazing systems over three seasons, measuring forage composition and circulating glucose and insulin concentrations in 12 Standardbred mares to determine whether restricted pasture access (rotational system with 0.4 ha paddocks) altered carbohydrate metabolism compared to unrestricted grazing. Contrary to expectations, grazing system did not influence water-soluble or ethanol-soluble carbohydrate content, nor did it significantly affect plasma glucose or serum insulin concentrations; however, season proved far more influential, with glucose peaking at 105.6 mg/dL in August and insulin concentrations highest in October (0.21 µg/L). The findings suggest that pasture management approach alone is insufficient to modify glucose metabolism in grazing horses, whereas seasonal fluctuations in forage composition—particularly fibre content and crude protein—meaningfully drive metabolic responses, implying that practitioners should prioritise understanding their local seasonal pasture dynamics rather than assuming rotational grazing will reduce insulin exposure. For horses at metabolic risk, management focus should centre on temporal aspects of grazing opportunity and forage quality variation across the year rather than simply restructuring paddock rotation protocols.
Read the full abstract on PubMed
Practical Takeaways
- •Choice between continuous and rotational grazing does not meaningfully change a horse's glucose or insulin response—manage based on other factors like pasture preservation and parasite control
- •Season matters more than grazing system for metabolic management; autumn pastures warrant closer monitoring for insulin dysregulation in susceptible horses
- •Summer pastures present higher glucose challenge; horses with metabolic concerns may benefit from restricted grazing during peak season (June–August)
Key Findings
- •Grazing system (continuous vs. rotational) did not significantly affect plasma glucose or serum insulin concentrations in horses
- •Season significantly affected glucose and insulin dynamics, with glucose highest in August (105.6 mg/dL) and insulin highest in October (0.21 μg/L)
- •Water-soluble carbohydrates were highest in June and lowest in August/October, correlating with seasonal forage maturity
- •Crude protein was lower in rotational grazing compared to continuous grazing (P = 0.04), but this did not translate to metabolic differences