We know that obesity and metabolic disease in horses often go hand-in-hand, but does obesity cause metabolic disease or is it the other way around? A group of researchers from the Swedish University of Agricultural Sciences recently set out to determine the answer.

Veterinarians know that high-starch and -sugar diets can decrease insulin sensitivity (IS) and lead to insulin resistance (IR), which is also an indicator of equine metabolic syndrome (EMS). The research team hypothesized that weight gain resulting from a low-starch and -sugar diet would not negatively impact IS, and that unlimited pasture access would further decrease IS and cause hyperinsulinemia (increased blood-insulin concentrations).

The team employed nine sedentary Standardbred mares with moderate IR in their 30-week, five-part study, which included:

• Period 1: A three-week maintenance period;
• Period 2: Continual increase of forage low in water-soluble carbohydrates and supplemented with fat “to speed up the weight gain process, without adding more sugar to the diet,” said lead researcher and PhD student Sanna Truelsen Lindåse, DVM;
• Period 3: A diet consisting of 2.5 times daily maintenance requirement of metabolizable energy;
• Period 4: Adaptation to small grass paddock for one week; and
• Period 5: Four weeks of turnout in a 25-acre pasture during the growing season.

The researchers analyzed blood samples throughout the study period