Study Evaluates Equine Fecal pH during Abrupt Feed Changes

A team of researchers in New Zealand recently set out to determine how dietary changes--from pasture to harvest forage and concentrates--affected fecal pH and certain bacterial populations of the hindgut.

It's known that abrupt changes in a horse's diet can have an adverse effect on a horse's health, especially in the large intestine. Because resident microbes in the large intestine react to dietary changes, upset can result in digestive and/or metabolic complications, such as hindgut acidosis (abnormally high acidity in the hindgut) or laminitis. These changes can be measured by hindgut pH levels and the bacteria species present.

Mariette van den Berg, MSc, an equine nutritionist in New South Wales, Australia, and a team of researchers from Massey University, in Palmerston North, New Zealand, employed six Thoroughbred fillies accustomed to grazing perennial ryegrass and white clover with no additional feed supplementation.

The team removed the horses abruptly from pasture and housed them individually for 13 days. During this period the fillies consumed a diet of ryegrass/clover mixed hay, alfalfa chaff, a pelleted concentrate, and crushed barley. They increased the ratio of concentrate (pellets and barley) to conserved forages over the 13-day period, van den Berg noted.

After 13 days, the researchers returned the horses abruptly to pasture for an additional three days. During the entire study period, the team collected fecal samples daily for pH analysis and every second day for bacterial population.

Researchers found that although the horses' diets were changed rapidly from solely pasture to hay and concentrate and back again, fecal pH levels did not decrease significantly during each dietary change. Van den Berg also noted that the team observed a negative linear effect of fecal pH and increased concentrate to forage ratio, even with the noted increase in Streptococcus and Lactobacillus populations in the fecal samples. This indicated that conditions in the hindgut were acidic, which puts them at risk for hindgut acidosis.

The team also found that, although the fillies were receiving a high enough level of concentrates to be at risk for hindgut acidosis, no such complications were observed. Van den Berg believes this is because the team mixed chaff with the concentrate, which slowed the fermentation rate in the hindgut and increased fecal pH.

The team cautioned that the study was performed during the spring when pasture was high in water soluble carbohydrates and low in fiber, which likely led to a lower fecal pH. Additionally, the horses in this study were previously exposed to concentrates in their diets, which could have allowed them to cope easier with the abrupt diet change.

Van den Berg and colleagues stressed that microbial hindgut populations can be adversely affected by a change in diet from pasture to concentrate and hay, which can lead to digestive upset. They recommended that owners make any dietary changes gradually to prevent potential digestive and metabolic disorders in their horses.

The study, "Fecal pH and Microbial Populations in Thoroughbred Horses during Transition from Pasture to Concentrate Feeding," will appear in an upcoming issue of the Journal of Equine Veterinary Science. The abstract is available online.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.