The fattening associated with grazing horses on cultivated high-yielding pasture induced only moderate changes in glucose, insulin and fatty acids as measured in a glucose tolerance test, a Finnish study has shown.
The researchers said the moderate changes recorded did not compromise the ability of the horses to control plasma glucose concentrations or adipose tissue lipolysis – the breakdown of lipids into glycerol and free fatty acids.
“The body condition score and weight gain during the grazing season were not associated with increased insulin resistance,” Kari Elo and his colleagues reported in the peer-reviewed open-access journal, PLOS ONE.
They said their findings supported the hypothesis that obesity and severe hyperinsulinemia – too much insulin in the blood – are required to produce change in the insulin resistance status of horses.
The team used a group of 16 Finnhorse mares, a native cold-blooded breed, which was split between cultivated high-yielding pasture and semi-natural grassland. They assessed the animals in terms of their body-condition score, fat changes around the neck and tailhead, and their results in an intravenous glucose tolerance test.
The horses on the higher quality pasture certainly moved toward the overweight end of the spectrum during the grazing period, which ran from the end of May to the start of September, but that did not in itself have much influence on their pre-existing levels of insulin sensitivity, the researchers found.
“Our results indicate that grazing on cultivated high-yielding pasture does not increase the risk for metabolic diseases in Finnhorse mares that have a normal body condition score at the beginning of the grazing season,” they reported.
Obesity and insulin resistance are known to be risk factors for laminitis, they said, and are associated with equine metabolic syndrome.
Selim S, Elo K, Jaakkola S, Karikoski N, Boston R, Reilas T, et al. (2015) Relationships among Body Condition, Insulin Resistance and Subcutaneous Adipose Tissue Gene Expression during the Grazing Season in Mares. PLoS ONE 10(5): e0125968. doi:10.1371/journal.pone.0125968