Horses affected by equine asthma can benefit from being fed soaked hay, but researchers have sounded a note of caution.
It should be fed out immediately, they say, due to increases in yeasts, and typical bacteria and mold over the 24 hours after soaking.
Steamed hay showed more stability over a similar time period, Maren Glatter and her fellow researchers at Martin Luther University Halle-Wittenberg in Germany reported.
The study team, writing in the journal Animals, said horses suffering from equine asthma must consume low-dust forage, with soaking and steaming both considered suitable methods of hay treatment. Both treatment methods can rinse off dust and reduce the viability of micro-organisms.
However, the impacts of this treated hay’s subsequent storage and their effects on the horses’ chewing activity are largely unknown.
In their research, six healthy Warmblood mares were fed either dry, soaked or steamed hay in a crossover study design. The horses were fitted with a modified halter fitted with a pressure sensor and data logger to monitor chewing.
The soaked hay in each case had been immersed in water at 10–15 degrees Celsius for 15 minutes. The steamed hay was subjected to 100-degree temperatures for an hour.
Microbial counts were determined by culture before and after soaking or steaming, and subsequent storage at 10 degrees and 25 degrees for 6, 12 and 24 hours.
Both treatment methods reduced counts of typical bacteria, they reported.
Typical fungi species were detected in the dry hay, but within recommended benchmark levels. Soaking reduces the presence of fungi species initially, but they increased during subsequent storage. In contrast, no typical fungi were detected in the hay samples direct out of the steamer.
Typical fungi increased exclusively in the soaked hay in the following 24 hours, particularly at the higher storage temperature.
The soaked hay also had high yeast counts, although still within the recommended benchmark. These levels increased with storage time and with increasing storage temperature. In the steamed hay, no spoilage fungi or yeast were found, and only one typical mold was detected.
Overall, steaming reduced typical molds and yeasts better than soaking, but storing soaked hay elevated levels of micro-organisims.
Both the steamed hay and soaked hay were eaten slower than the conventional dry hay.
The steamed hay was chewed the most intensely, with 3537 chewing cycles per kilogram of dry matter for the steamed hay, 2622 chewing cycles for the dry hay, and 2521 chewing cycles for the soaked hay.
“Steaming particularly improves the hygienic quality of hay,” they said.
Steamed hay, they said, was “almost stable” during storage during the 24 hours that followed, but soaked hay was not, with increases in yeasts, and typical bacteria and mold.
“The feeding of soaked hay is recommended directly after treatment, to avoid hygienic problems.” It should not be left to dry out, they added.
The study team noted that the intake of soaked hay was characterized by a particularly low rate of consumption rate and high chewing intensity. While this may have a positive impact on the dental and gastrointestinal health of the horse, it may have been driven by reduced palatability.
In conclusion, the authors said high-quality hay is recommended feed for horses and it generally does not need to be treated.
However, if only hygienically poor hay is available, or the horse may be prone to conditions such as asthma, then soaking or steaming might be helpful.
“This, however, needs to be considered in the context of any subsequent storage. Soaking hay reduces microbial cell counts, but a long storage duration in combination with warm temperatures amplifies the proliferation of spoilage-indicating molds and yeasts in the soaked hay.
“Steaming is very effective concerning the improvement in hygienic quality, and steamed hay is less susceptible to spoilage during storage.”
Soaking, they noted, led to a higher reduction in water-soluble nutrients than steaming, which can be positive or negative, depending on the kind of nutrient and the health precondition of the horse in question.
Dietary adjustments, balancing energy, amino acids, and minerals, might be required when feeding soaked and, to a lesser extent, when steamed hay are fed, but this would be difficult to implement in practice, they said.
The study team comprised Glatter, Mandy Bochnia, Monika Wensch-Dorendorf and Annette Zeyner, all with Martin Luther University Halle-Wittenberg; and Jörg Michael Greef, with the Federal Research Center for Cultivated Plants, Crop and Soil Science, at the Julius Kuehn Institute in Germany.
Glatter, M.; Bochnia, M.; Wensch-Dorendorf, M.; Greef, J.M.; Zeyner, A. Feed Intake Parameters of Horses Fed Soaked or Steamed Hay and Hygienic Quality of Hay Stored following Treatment. Animals 2021, 11, 2729. https://doi.org/10.3390/ani11092729