Winter hay to spring grass: Tips for a smooth transition

As winter winds down and soil temperatures start to rise, spring grass pops up all over. Our equine partners eagerly start seeking out this lush, soft, green grass. However, many owners worry about this sudden transition from a rather bland winter hay ration to green spring pasture. On the other hand, when hay resources are running low, it may be tempting to just let them be — especially given the scarcity of hay this year!

In this post, we’ll explore the challenges of managing grazing horses in this season and provide practical tips for a smooth and safe transition to spring grass.

Understanding the issue: Winter hay vs. spring grass

As grass matures throughout the growing season, the protein content decreases, while the fiber fraction and dry matter content increase, resulting in an overall decrease in digestibility and digestible energy.

It therefore makes sense for early spring grass to be higher in protein, and higher in easily fermentable carbohydrate content, than the grass used to make hay, which was allowed to grow later into the season before being cut. Of course, hay will be much lower in moisture compared to fresh grass as well.

The combination of these factors sets the stage for potential digestive upset when there is an abrupt switch from hay to spring pasture. That’s a big problem, given the overall importance of gut health for horses.

Why, you ask? Well, let’s do a quick calculation.

Depending on the variety of the grass, early spring grass can be as high as 20% or more in protein. That same grass, cut later for hay, may test around 10% to 14%. We know that the majority of the average horse’s nutrients will be supplied by their forage. So, as an example, let’s say there is a 6% protein difference between our hay and our spring grass. An increase in forage protein content of 6% equates to just over a pound of additional protein consumed by the horse each day. That seemingly small change in protein content alone can almost cover the protein requirements of the average horse. Consider that the horse is now consuming that in addition to what they were getting from the hay alone.

The same goes for other nutrients passing through the digestive tract. When combined with the higher digestibility of spring grass due to its rapidly fermentable fibers, it all represents a large and potentially abrupt change in the influx of nutrients into the hindgut. This change in nutrient influx can disrupt the delicate balance of gut microbial organisms. The highly specialized and sensitive hindgut microbial population requires time to adapt to feeding changes to avoid metabolic issues. And so, as with all nutritional changes in a horse’s diet, a gradual change is ideal when moving from hay to fresh grass.

Strategies for a successful transition

Spring grass often sprouts and grows rapidly, making it difficult to accurately determine how much horses are really consuming when they have full access to pasture — but with good management, you can help to keep the transition gradual. Here are some different approaches to gradual transitions that may suit your management situation and personal preferences:

1. Keep some hay in the pasture: Start by making hay available in the pasture for the first couple of weeks, regardless of access to fresh grass. The fresh grass is lower in fiber, so horses can manage their fiber needs by going back and forth between the two forage sources.
2. Manage turn-out time: If your horse is stalled, consider reducing the amount of time they are turned out on grass and then gradually increasing it as spring progresses. This is an easier option for those who have dry lots or other areas, to make sure horses spend enough time turned out while also restricting access to grass.
3. Consider a grazing muzzle: Horses that are exclusively kept out on pasture can also be managed with a grazing muzzle. Another option, for horses kept out on large pastures, is the use of temporary fencing to restrict access, but be aware that the fencing will need to be moved frequently.

Some horses require careful oversight

Horses diagnosed with equine metabolic syndrome (EMS) conditions, a history of pasture-associated laminitis, foundering, and so forth, present a different set of challenges. They require particularly careful management during this time, should some access to a dry lot, or careful restriction practices such as muzzles or time-of-day turnout, not be possible. Depending on the individual horse’s condition, turnout on spring pasture may not be desirable regardless of the restrictions implemented.

Some horses may lose a little weight in the early days of spring, specifically the picky ones that prefer soft new grass over hay. That weight should be gained back rapidly as pasture growth rate accelerates and you can give them free access. Keep in mind, though, that mares in late pregnancy or lactation need to be monitored more closely. They have higher nutrient requirements and benefit from the more nutritious grass.

The magic number is two … or perhaps three?

For the best support of horse health throughout, the hay-to-grass transition is implemented over a two-week period. This allows those hindgut microbial communities to adjust without deleterious effects. If your horse has been fed only hay over the winter, with absolutely no access to pasture, start out more conservatively, extending the adaptation period to three weeks if needed.

Keep in mind that the area you live in will dictate when and how quickly your spring grass arrives, and this will influence your transition plans. Some areas have sparse pastures as compared to more lush areas such as Central Kentucky. Regular evaluation of your horse’s condition and your forage quality and quantity during this period are crucial to making informed adjustments to the transition plan.

Keeping these principles of equine nutrition in mind will empower you to plan for and oversee a healthy transition from winter hay to spring grass. By embracing a gradual approach and tailoring strategies to your horse’s needs, you can ensure a smooth and healthy transition, allowing them to fully enjoy spring pasture.

About the author: 

Originally from South Africa, Dr. Mieke Holder is a senior research scientist at Alltech. Her research focuses on equine nutrition and the use of Alltech technologies to improve feed and nutrient utilization, horse health and environmental sustainability. Prior to joining Alltech, Dr. Holder was a faculty member at the University of Kentucky, focusing on the environmental impact of grazing livestock. She earned her bachelor’s degree and master’s degree in animal sciences from the University of Pretoria, South Africa, followed by a Ph.D. in equine nutrition from the University of Kentucky.

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