The differences between Hay and Haylage: The Production Process

Written by Briony Witherow MSc RNutr. FHEA

As grass growth is seasonal, and our horses’ needs are not, we need to have a way of preserving grass to ensure a constant year-round supply.

There are two main methods of forage conservation: controlled fermentation where the pH is reduced to a level where growth of bacteria stops, or dehydration, where moisture content is decreased to reduce microbial activity. Hay is an example of forage that is conserved using dehydration. The main challenge with preserving forage in this way being that it requires a longer period of dry weather to produce, whereas haylage is an example of grass preserved using controlled fermentation (along with silage).

As a rule of thumb, when considering the digestibility of a forage, as grass maturity and yield increase, digestibility decreases (containing more lignin). So, while very young grass in a growing state is much more digestible (picture lush pasture), if hay or haylage were to be made at this point, yields would be very low (imagine mowing your lawn). There is, however, a point in between these two stages where a balance can be struck between digestibility and yield.

Conservation Method

While both hay and haylage are made of the same ingredient, grass, they are persevered using different methods. This has a direct impact on their key features as a product: hay being preserved through dehydration has a much higher dry matter (lower moisture content) at over 80%, compared to a typical haylage with a dry matter of between 40 and 60%.

The Production Process

Many of the differences between hay and haylage can be attributed to the conservation process, the first distinction of which is timing. Hay is typically harvested from the end of May to the end of July, cutting dates for more natural swards (meadow hay for example) likely to be later still. Haylage on the other hand tends to be cut earlier in the season (typically before mid-June). For haylage, it is essential that there is sufficient moisture content to facilitate complete fermentation, making later (more lignified and drier) cuts challenging. For hay and haylage, harvest time is also heavily dependent on location (altitude, aspect, climate); forage at higher altitudes being cut later than those at lower levels.

Forage is often described by ‘the cut’ – early or late, first or second – and being able to understand the potential implications of this is essential when making buying decisions. In the crudest sense, late or early cut refers to whether the grass is cut earlier, in a more vegetative (growing) state which is typically more digestible, or later, in a more mature state which tends to be more fibrous and less digestible.

The first or second (or even third) cut refers to whether it is the first crop taken or a subsequent cut from a particular field. This tends to refer to more intensively grown hay or haylage crops which are cut once (usually very early in May), then left for 30-45 days and what is regrown is then cut again (July time). While the cut of hay or haylage can impact its nutritional properties, the maturity of the grass that is the most influential nutritional factor when selecting forage.

Hay requires a minimum curing period of 3 days (in optimum conditions, ~30 hours of sunshine), while haylage requires only 1-2 days. In the UK the reality is that most hay is in the field curing for a week or more which carries with it risk of losses (nutritional and hygiene). It is estimated that the average number of suitable hay drying periods in Southern England is two to three opportunities per year – emphasising why it can be so difficult to source high quality hay.

Hay is baled when it contains 65-80% dry matter in comparison to haylage at 45-50% dry matter, and the dry matter level when baled can also vary depending on the size and shape of the bales.

Once haylage is baled it needs to be wrapped within 4-6 hours and it is key that the seal achieved is airtight (typically 6-8 layers of plastic) – if air can penetrate the bale, mould will be able to grow. The absence of air (anaerobic environment) is crucial to pause microbial activity and therefore preserve the grass for feeding.

The process where forage is preserved using fermentation is called ensiling. During this process lactic acid bacteria ferment water soluble carbohydrates (WSC) to organic acids under anaerobic conditions. During this process, the pH decreases from around 6 to around 4 which stops detrimental anaerobes, stabi6lising the product, and in doing so preserving the forage. The WSC and moisture content are therefore essential to the ensiling process, a lack of either causing potential for incomplete fermentation. The ensiling process is considered complete after ~3-6 weeks, where fermentation of WSC has ceased (either due to a low pH or lack of sugars), at this stage the temperature drops to ambient, and the product is considered stable.

While traditionally hay is left to cure for a few weeks before feeding, if moisture content allows (dry matter more than 86%), it can be fed straight off the field. In the UK, as conditions often may not allow for moisture content to be reduced sufficiently before baling, it is best to wait 4-6 weeks prior to feeding to ensure any residual microbial activity has ceased. If hay is stored properly then it can be fed after several years, but it won't be as nutritious as it was when it was first made. It may also be dusty and if so should be soaked (10-20 minutes) or steamed before feeding. Poorly stored hay is often unsuitable to feed to horses.

Haylage needs to ferment, so it should not be fed straight after being baled and wrapped. The amount of time it takes to 'cure' is variable depending on the moisture and WSC content of the grass when it was wrapped, but a good guide is 6 weeks. Sealing the haylage simply pauses microbiological activity so bales should always be checked for damage prior to opening and once opened must be used within 3-6 days (depending on the type of haylage and time of year).  It is worth noting that high temperature steaming can help to extend this ‘shelf-life’.