Glucose and Insulin Responses in Horses to Various Pasture Grasses

Managing metabolic responses of horses to forage is an ongoing challenge for horse owners and veterinarians throughout the year.

Spring and late fall grasses are particularly high in non-structural carbohydrates (NSCs) due to photosynthesis outpacing utilization in months when lower temperatures slow plant growth. NSCs tend to elevate glucose and insulin levels in grazing horses.

Alfalfa and teff (an annual warm-season grass) tend to be lower in NSC concentrations due to “a self-limiting carbohydrate storage mechanism.”

Editor’s note: Teff is a fine-stemmed, leafy and soft palatable grass, with a forage quality similar to timothy grass. It also called annual bunch grass or Williams lovegrass.

A Minnesota study looked at the responses in six aged mares (22-26 years old) to a variety of forage types:

• alfalfa versus mixed, perennial cool-season grass (CSG of orchard grass and Kentucky bluegrass) in spring
• CSG versus teff in the fall

When not grazing, the mares had access to alfalfa, CSG and teff in two daily feedings [DeBoer, M.L.; Hathaway, M.R.; Weber, P.S.D.; Sheaffer, C.C.; Kuhle, K.J.; Martinson, K.L. Glucose and insulin response of aged horses grazing alfalfa, perennial cool-season grass, and teff during the spring and late fall, Journal of Equine Veterinary Science (2018), doi: https://doi.org/10.1016 j.jevs.2018.10.027].

Evaluation of the results revealed that “there were no differences in the glycemic or insulinemic responses in the spring when comparing horses grazing alfalfa or CSG.”

However, differences were observed in the fall. Teff-grazed horses had lower glucose and insulin responses compared to CSG-grazed horses.

The study concluded: “Teff appears to offer an alternative pasture forage to CSG in the late fall for horses requiring an attenuated glucose and insulin response.”