Effects of Soaking on Protein, Mineral Loss in Hay

Providing a diet low in nonstructural carbohydrates (NSC), such as sugars and starch, is key to maintaining horses diagnosed with diseases such as laminitis, hyperkalemic periodic paralysis (HYPP), and polysaccharide storage myopathy (PSSM). Soaking hay not only helps reduce dust, but also NSC, making it a popular option for maintaining horses with these health issues.

But could soaking have other undesired effects on hay? To find out, researchers recently investigated the impact of water temperature and soaking duration on protein and mineral concentration in orchardgrass and alfalfa hay.

Previous research has suggested that laminitic horses should consume a diet containing less than 12% NSC and PSSM horses should eat a diet containing less than 10% NSC. In addition, reduced potassium (K) intake is essential for horses affected by the genetic disorder HYPP, and veterinarians recommend a diet containing less than 1.1% K for affected animals. Although soaking hay is thought to reduce both NSC and K concentrations, additional essential nutrients might be lost inadvertently.

In this study, a research team led by Krishona Martinson, PhD, assistant professor and equine extension specialist in the Animal Science Department at the University of Minnesota, tested four different hay types commonly fed to horses in the Midwest:

  • Second cutting, early bud alfalfa;
  • First cutting, flowering alfalfa;
  • Second cutting, vegetative orchardgrass; and
  • First cutting, flowering orchardgrass.

Researchers assigned one flake from each bale type to each treatment group, which consisted of soaking for 15, 30, or 60 minutes in either cold (22°C) or warm (39°C) tap water, and 12 hours in cold tap water. After treatment, the researchers analyzed the hay's carbohydrate fractions, crude protein, calcium, phosphorus, and magnesium concentration. They compared all treatments to a nonsoaked control.

Key findings from the study included:

  • Soaking did not affect crude protein concentrations in alfalfa bud or flowering orchardgrass hay;
  • As soaking time increased, crude protein increased in the vegetative orchardgrass (due to leaching of other nutrients that concentrated crude protein) and decreased in flowering alfalfa;
  • Phosphorus, potassium, and magnesium losses were reported in all hays with longer soaking times;
  • As soaking time increased in alfalfa-bud and vegetative orchardgrass, calcium concentrations decreased;
  • Potassium concentration in the flowering orchardgrass and both alfalfa hays decreased when hay was soaked in warm water; and
  • Warm water soaking lowered magnesium concentration in alfalfa bud soaked for 60 minutes and flowering orchardgrass soaked for 30 minutes.

The team noted that soaking for 15 to 60 minutes did not reduce hay nutrient content below recommended values for a 500 kilogram (about 1,100 pound) horse in light work. However, with increased soaking time, the calcium to phosphorus ratio became elevated due to the reduction in phosphorus concentration.

Martinson and colleagues recommended owners of horses diagnosed with laminitis, HYPP, or PSSM have their forage analyzed to determine the appropriate hay for their horse. When necessary, hay should be soaked for short durations (15-30 minutes) to prevent other nutrient deficiencies, she noted.

The study, "The Effect of Soaking on Protein and Mineral Loss in Orchardgrass and Alfalfa Hay," was published in December in 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.