Lush spring pasture might look inviting to your horse after a long, cold winter filled with piles of hay. But grazing it can increase a horse’s body condition to the point of obesity and potentially cause laminitis—both of which, we know, can have serious health consequences.

But how do changes in body condition during the grazing season affect insulin dynamics and the expression of genes associated with obesity and insulin resistance?

To find out, Kari Elo, PhD, and colleagues from the University of Helsinki, in Finland, assigned 22 Finnhorse mares to graze either a cultivated high-yielding pasture (CG) or semi-natural grassland (NG) for 24 hours each day from May to September. The CG pasture consisted of tall fescue, timothy, and meadow fescue. The NG pasture contained meadow fescue, meadow foxtail, tufted hairgrass, timothy, white clover, dandelion, and meadowsweet.

The team conducted an intravenous glucose tolerance test and gene expression profiling at the beginning and end of the grazing period on eight mares from each grazing group. After a 12-hour fast, the team collected jugular blood before the mares received intravenous glucose and again at various intervals following infusion for future analysis. Additionally, they measured those eight horses’ body weight, body condition score, waist circumference, and subcutaneous fat thickness at the neck and tailhead at the beginning and end of the trial