Effect of Hay Soaking on Nutrient Content

As detailed in the article, I have never liked soaking hay for horses with equine asthma as there are much better ways to handle the problem. Here is one reason to find alternatives.
DrO

Effect of Hay Soaking Duration on Metabolizable Energy, Total and Prececal Digestible Crude Protein and Amino Acids, Non-Starch Carbohydrates, Macronutrients and Trace Elements
J Equine Vet Sci. 2021 Jun;101:103452.
Authors
M Bochnia 1 , C Pietsch 1 , M Wensch-Dorendorf 2 , M Greef 3 , A Zeyner 4
Affiliations

1 Martin Luther University Halle-Wittenberg, Institute of Agricultural and Nutritional Sciences, Group Animal Nutrition, 06112 Halle (Saale), Germany.
2 Martin Luther University Halle-Wittenberg, Institute of Agricultural and Nutritional Sciences, Biometrics and Informatics in Agriculture Group, 06112 Halle (Saale), Germany.
3 Julius Kuehn Institute, Federal Research Center for Cultivated Plants, Crop and Soil Science, 38116 Braunschweig, Germany.
4 Martin Luther University Halle-Wittenberg, Institute of Agricultural and Nutritional Sciences, Group Animal Nutrition, 06112 Halle (Saale), Germany. Electronic address: annette.zeyner@landw.uni-halle.de.

Soaking hay before feeding has been documented to reduce airborn respirable particles and water-soluble carbohydrate (WSC) content which may have positive benefits for horses suffering from Equine Asthma (EA) or Equine Metabolic Syndrome (EMS). Prolonged soaking also leaches minerals, but to-date no measurement of the loss of small intestine digestible crude protein has been documented. One aim of this study was to investigate various soaking durations on nutrient contents of hay, WSC, macronutrients, and trace elements levels. Another objective was to determine the prececal digestible crude protein (pcd CP) and amino acid (pcd AA) fraction contents and prececal digestibility (pcD). Four different batches of meadow hay were soaked in water (20° C during preparation) for 0 minutes, 15 minutes, 30 minutes, 60 minutes, and 12 hours and drained for 20 minutes. A 15 minutes soaking duration significantly reduced the levels of nearly all investigated nutrients (e.g. for fructans, and WSC, macronutrients and trace elements). However, the crude fiber, acid detergent fiber (ADF), and acid detergent lignin content increased. Metabolizable energy (ME) contents decreased by 5-15 %, pcd CP and pcd AA fell by 35 %, and the pcD declined by up to 49 %. In contrast, the pcD was 56 % before soaking. Longer soaking durations did not enhance the wash-out effect. Horse owners should be aware that soaking hay, regardless of reason, may negatively alter the nutritional value. The wide range of wash-out effects may pose risks in calculating the correct dry matter portion to prevent weight loss and maintain ME, pcd CP and pcd AA requirements, especially for horses with EMS and EA.

Keywords: Hay; Nutrient composition; Prececal digestible crude protein; Soaking, Water soluble carbohydrates.