Soaking Hay : What's The Latest?

Soaking hay before feeding is typically done for two reasons. The first being to reduce airborne dust particles, and the second to reduce water-soluble carbohydrates (WSCs) as a management tool for horses prone to metabolic conditions. However, the ‘optimum,’ length of time that a forage should be soaked for is a subject that is often debated and still does remain unclear. Soaked forages have been associated with a decrease in nutrients, as well as an increase in the bacterial profile, increasing the potential risk of other health issues.

Water-Soluble Carbohydrates

For horses suffering with metabolic conditions, guidelines suggest that the diet as a whole should not exceed more than 10% water-soluble carbohydrates (WSC). It is well known that soaking forage will reduce the WSC content, and so many owners will adopt this practise as a means of reducing their horses daily intakes.

Recent research investigated the effect of soak time on 4 different hay samples at a duration of 0 minutes, 15 minutes, 30 minutes, 60 minutes and 12 hours. These hay samples were soaked in water at 20 degrees, and then allowed to cool at a room temperature of 21 degrees. After just 15 minutes, the WSC content of the forage was reduced by 17%, and this did not decrease further with the longer soak times. As the forage initially had a relatively low WSC content, this decrease was also deemed to be reduced sufficiently enough to be suited to horses with a metabolic condition (10-12% WSC). However, soaking for 15 minutes also reduced the metabolizable energy (ME), crude protein and amino acid content of the hay. Macronutrient and trace element minerals were also lost after soaking the hay for 10-15 minutes, and the overall ADF value of the hay increased, indicating a reduced digestibility. For horses on soaked or restricted rations, feeding a fortified feed will be essential to ensuring nutrient requirements are being met (Bochnia et al, 2021).

By comparison, a further study in the UK went onto soak hay for periods of 20 minutes, 40 minutes, three hours, or 16 hours. The briefest soaking removed an average of about 5% of WSC, while the longest soaking removed 27%. Finally, regardless of soaking time, there was no correlation between the original WSC content in a particular hay and the percentage of reduction after soaking.

For horses who are suffering with a metabolic condition that requires WSC intakes to be restricted, having the forage analysed in the first instance can be a helpful way of determining how suitable the forage is ahead of soaking, so that soak times and potential nutrient losses can be reduced.

Respirable Particles

Another survey investigated the effects of soaking hay as a management for horses with respiratory conditions, such as COPD or RAO. Hay that was found to be immersed in water and fed immediately after led to a 60% reduction in respirable particles in the horses breathing space when compared to dry hay. In addition, soaking for 30 minutes reduced the number of respirable particles by about 90%, but also reduced the Na, K and P content of the hay. Soaking for a longer period, at least up to 12 h, did not give a significant further reduction in number of respirable particles but there was loss of Mg and further losses in Na, K, and P.

Bacterial Changes

The horse is known for having a particularly sensitive gut microbiome which is very sensitive to change. In one study looking at the effect of wetting numerous different hays, the average bacterial contamination across all hay samples increased by up to 5 times when the hays were soaked for 9 hours in water (M Colyer et al, 2014). Further studies have also identified that the ingestion of bacteria on feed stuffs is accompanied by ingestion of significant levels of lipopolysaccharides (LPS) which can potentially elicit a negative immune response in animals. In human studies, increases in LPS have been noted in diseased states, and so increasing ingestion bacteria and consequently LPS, should be avoided. The research results showed increased proteobacteria from 46% on the dry hay to 67% after 12 hours soaking. Feeding long soaked hay may therefore risk ingestion of bacteria greater than the proposed safe upper bacterial limit of 20 μg/g for animals. The study also went on to establish that steaming the hay for 50 minutes following soaking greatly reduced the microbial contamination by up to 90 % (S. Daniels, 2020).

Further research is required to investigate the survival of feed bacteria through the digestive tract, as the acidic environment may destroy certain bacteria populations. However, as horses commonly suffer gastrointestinal upset following changes of hindgut bacteria, it would be reasonable to suggest that bacteria load may have a major impact on gut health.

Need further guidance?

If you are unsure on how much forage your horse or pony should consume on a daily basis or need further assistance, please call our nutritional team on 01622 718487, or take a look at our horse & pony weight chart as a guide.