Going Green: Are Equine Diets Environmentally Friendly?

When most caretakers develop a diet for their horses, the environmental impact of the comestibles once they're passed through the horse's body often isn't the first thing they consider. But a team of researchers recently set out to see which forage-based diet is healthiest for both the horse and the environment.

Protein, a key factor many horse owners consider when choosing a feed, is often inadvertently fed in excess of the horse’s nutritional needs. This can lead to increased nitrogen (a component of protein) in the urine, which can cause ground water contamination and poorer air quality.

The Michigan State University (MSU) research team recently completed a study comparing the protein quality of several commonly fed equine diets and the horse's utilization of the dietary protein. They aimed to determine which diet best met protein requirements without leading to excess nitrogen excretion. 

Nathalie Trottier, MS, PhD, associate professor of monogastric animal nutrition in the MSU Department of Animal Science and principle investigator of the study, explained, “In order to determine nitrogen utilization by the horse, you first need to measure the difference between the amount of nitrogen being consumed and the amount being excreted.”

In the study, researchers fed six mature Arabian geldings in moderate exercise six different diets (each of which they analyzed beforehand to determine protein content) over six 14-day time periods.

The diets included:

  • Full-bloom timothy grass hay (first cutting);
  • Timothy grass hay + 0.2% body weight oats;
  • Timothy grass hay + 0.4% body weight oats;
  • Mid-bloom alfalfa (first cutting);
  • Early-bloom alfalfa (second cutting); and
  • Early-bud alfalfa (third cutting).

During the last three days of each feeding period, the team collected feces and urine and analyzed samples to determine the horses’ daily nitrogen excretion. They drew blood on the final day of each feeding period to determine amino acid concentrations and assess post-gut nitrogen utilization.

Key study findings included:

  • Apparent whole tract nitrogen digestibility was greater for horses fed alfalfa than those fed timothy hay diets;
  • Feeding alfalfa of decreasing maturity (mid-bloom, to early bloom, to early bud) exceeded protein requirement and significantly decreased post-gut nitrogen utilization, leading to increased urine volume and urinary nitrogen excretion;
  • Urinary nitrogen excretion was greater in horses fed alfalfa versus timothy hay diets; and
  • Feeding oats at 0.2% or 0.4% body weight with timothy hay met protein requirement and greatly enhanced apparent nitrogen digestibility without increasing nitrogen excretion relative to feeding second and third cutting alfalfa hay.

Trottier concluded, “When good quality grass hay availability is not limiting, feeding grass hay in combination with oats (if more calories are needed), is more environmentally desirable than feeding legume hay.”

The study, “Protein Quality and Utilization of timothy, oat-supplemented timothy, and alfalfa at differing harvest maturity in exercised Arabian horses,” was published in July 2011 in Journal of Animal Science. The abstract is available online

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