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 g