Many horse owners understand the important role nutritional building blocks, such as protein and minerals, play in young horses’ growth, but they might not consider the endocrine or metabolic consequences of their feed choices. In a recent study researchers compared the differences between a low glycemic (LG) and high glycemic (HG) meal’s effects on young horses’ growth hormone (GH) secretion.
Burt Staniar, PhD, assistant professor of equine nutrition at Pennsylvania State University, explained that the “growth hormone is important for a myriad of different functions, but modulating growth of the young horse is an important one during this time in a foal’s life. We hypothesized that an HG meal would result in a large rise in glucose and insulin, which would cause the pituitary to stop secreting GH, followed by a larger pulse of GH afterward."
In a crossover study of two 21-day periods, Staniar and colleagues fed 12 Quarter Horse weanlings two daily meals of either an HG meal (ground corn as main ingredient) or LG meal (soybean hulls as main ingredient). After five days of acclimatizing to each diet, weanlings received a total daily concentrate ration of three kilograms along with free-choice, mixed-grass hay and access to water. On Day 20, the researchers fitted the weanlings with a jugular catheter, and on Day 21 they measured GH secretion at 15-minute intervals for 24 hours.
Upon reviewing the study results, the researchers found that their data supported their hypothesis: The first GH pulse occurred an average 26 minutes later after the horses consumed HG meals as compared to when they ate LG meals. This initial GH inhibition resulted in larger GH pulses between meals and during the overnight period, leading to a 33% overall increase in GH secretion for horses consuming HG meals compared to horses consuming LG meals.
“There may be periods of time during growth when increased GH secretion due to concentrate feeding may increase the risk of skeletal growth disorders, perhaps during the rapid growth often observed in northern hemisphere-raised weanlings and yearlings in April, May, and June," Staniar explained. "But on the other hand, increased secretion due to concentrate feeding may also be beneficial or reduce the risk of the same disorders if present in the same animals during the winter months--November, December, January, and February--when growth normally slows considerably.”
The team noted that more research in this area is needed but that “these differences highlight the possibility that a more precise understanding of the metabolic consequences of the way we feed our young growing foals will likely provide those raising young stock better dietary control over growth, risk of disease, and ultimately the ability to succeed athletically.”
The study, “High glycemic and insulinemic responses to meals affect plasma growth hormone secretory characteristics in Quarter Horse weanlings,” was published in Domestic Animal Endocrinology in May.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.