Equine researchers have evaluated common horse feeds’ digestibility (the percentage of the digestion and absorption of various nutrients present in a feed source) primarily in mature horses, but little is known about the digestive capacity of young, growing horses.

Previous research suggests mature and young horses utilize high-fiber diets differently than adults, mainly because younger horses have a shorter retention time in the large intestine. A team of University of Kentucky (UK) researchers recently set out to compare the digestibility of a high-forage diet when fed to weanling versus mature horses.

The research team paired six weanling colts with six mature geldings (with an average age of 13.2 years) and allowed them to adapt for 21 days to a diet comprosed of 67% alfalfa cubes and 33% commercial concentrate.

On Day 1 of the study’s five-day collection period, Laurie Lawrence, PhD, professor of equine nutrition at the University of Kentucky, and colleagues fed each pair the same amount of two indigestible markers used to measure the average period of feed retention in the digestive tract (also called the mean retention time, or MRT)—called Co-EDTA and Yb—mixed with molasses and a portion of their concentrate for palatability.

The researchers then fitted the horses with fecal collection harnesses and offered the remainder of the concentrate and alfalfa cubes. The team collected feces from the harness every one to two hours throughout the entire collection period.

They analyzed all the fecal samples for the presence of the indigestible markers, as well as for dry matter (DM, calculated by the weight of