The horse hasn’t been born that doesn’t love alfalfa. Although it poses some balancing challenges, alfalfa can be a valuable addition to the diet. However, for reasons that are not yet explained alfalfa can cause flares of laminitis pain in some IR horses.
I have recently been asked about some information floating around the internet that claims to explain why this happens. The statements were that the carbon skeletons of amino acids and/or propionate used as a preservative on alfalfa would be converted to glucose and cause a blood sugar spike, just like feeding something that is too high in sugar or starch. Nice theory but it doesn’t hold up to scrutiny.
Gluconeogenesis is the process of creating glucose from precursors such as lactate, pyruvate, other derivatives of some amino acids and other substances like propionate. It occurs primarily in the liver, to a small extent in the kidney, and is a normal function. This is how all animals maintain normal blood sugar levels when glucose is not being absorbed from the intestinal tract.
The fault with the theory that high protein or propionate preservatives in alfalfa cause a blood sugar spike from gluconeogenesis is quite simply that they don’t. The carbon backbones of amino acids can themselves be directly burned for energy. If they, or propionate, are converted to glucose that glucose is not necessarily released into the blood. It can be stored as glycogen or fat if blood sugar is already normal. This process is under the control of the hormone glucagon.
Drs. Rodiek and Stull published a study on the glycemic index of common feeds in 1988. Glycemic index refers to how high blood sugar goes after eating. Oats is assigned a value of 100 and other feeds described as a % of the blood glucose level seen after feeding oats. They studied blood glucose levels for 5 hours after feeding 10 different foods to horses, including alfalfa. That study, and five others since, have clearly shown the blood sugar response to feeding alfalfa is extremely low.
As for propionate, a 1971 study by Drs. Argenzio and Hintz, two of the premier equine nutritionists in the last century, found that administering a load of propionate to ponies causes no rise in blood glucose in animals that had not been fasted. When fasted before the propionate was given, there was a increase in glucose from low levels to a low normal glucose level (70 mg/dL to 83.8 mg/dL on average). This is consistent with gluconeogenesis from the propionate but release of glucose regulated by glucagon to keep glucose well within the normal range – no spike.
So, while it remains true that alfalfa is problematic for some IR horses, the reason for this is still unknown.
Eleanor Kellon, VMD