Horses Can Smell Spring
/By Michael Hipp
The grass is growing. Can you smell it?
Your horse can.
Well, it seems like they can. I’ve always believed so and there are many scientific articles out this past year that are supporting that belief. But I digress. The fact is that the grass, as of February 17 in most of Snohomish County, has begun to grow, so if your horse is looking longingly at your pasture and salivating, that is the reason why.
You may be wondering how we can tell when exactly the grass begins growing, and that is a very good question. The T-SUM calculation was developed to determine the time when nitrogen can first be applied in the spring to assist crops and grasses to produce their best yields. This was done through experiments in both The Netherlands and The United Kingdom which were then validated in western British Columbia in the late 1980’s1. The calculation is a fairly simple one that just requires good data-keeping. It begins by measuring the average daily temperature in Celsius – meaning adding the high and the low that day and dividing by 2. For example, if the high for the day was 4 C and the low was 2 C then the average would be 4 + 2 = 6 / 2 = 3 C. There is one additional rule: if the average for a day is a negative (such as -2) then that will be counted as 0. You do this calculation every day starting January 1 and keep track of the result for every day. The T-SUM is all of the days’ numbers added together, and when that summation reaches 200 then the soil temperature is considered to be at the point where grass can begin to grow and, in the original intent of the T-SUM, nitrogen can be applied. You can use this calculation to plan and anticipate from year to year when your grass will begin to grow and when the best time to apply fertilizer is – as long as the soil can take the weight of your tractor, of course.
Typically in Snohomish County we reach T-SUM 200 by mid-February. I’ve seen dates as early as February 2 and as late as February 24. Now that you know that this time of year the grass is beginning to grow and calls out to your horse like the Sirens to the Argonauts, you may be a little more forgiving of their behavior. But for how long do you have to endure their pathetic cries for green pasture? That is another, and very important, good question. To answer that we must expand our focus from the grass itself to both the soil and the horse in order to avoid hurting either or both.
The time when you can turn your horse out to pasture after winter confinement will vary, sometimes greatly, depending on things like soil type, weather, drainage on your particular landscape, and such, but the primary focus is on soil moisture. When a soil is too moist or saturated it is at the greatest danger for compaction. That is because an overabundance of moisture in the soil weakens soil structure, and when weight is put on it, especially the weight of a horse, that soil will give way and collapse onto itself. This collapse, or compaction, will destroy all the small air pockets within the soil, suffocating the microbes and other biological creatures that the plants need to help break down and transport nutrients to their roots. This compaction will also suffocate the roots of the plants and slowly kill them off, despite any green parts it may have above the compacted surface. It is for this reason that I strongly encourage following the practice of walking out to your pasture and checking it before you turn horses out. Look down as you walk and if you leave footprints, especially footprints with water in them, it is too early. Only when you can walk across a pasture without that is it a good time to turn out.
Another thing to make sure of before turning your horse out for the first time is that the grass is the right height. Make sure the grass is between 8 to 10 inches in height before turning out your horse. Then make sure to remove them from the pasture when the grass height is about 3 inches, in order to preserve the health of the grass and its root system. Keeping the grass between 3 and 10 inches during the grazing period not only protects the grass but it also makes sure that the grass can filter any manure left behind and protect the soil from erosion. Another thing you can do to protect the natural resources around the pasture from manure and sediment runoff is to make sure your fences are a good distance away from any creeks or “seasonal streams” you may have, and that the area between the fence and those waterways is planted with native plants to act as a buffer for any runoff from the pasture.
Once you have determined the soil is safe for the horses to walk on and the grass is the right height for grazing, we need to focus on that which I’m sure you have the most invested in – your horse. Remember that over the winter your horse has had good hay, but no fresh grass. Introducing fresh grass to your horse has to be done slowly because when a horse eats too much fresh grass too early in the spring, especially after a winter confinement diet of hay only, colic and laminitis will most likely occur. If you’ve never had colic or laminitis happen in your horse trust me – you don’t want either one.
So what is the big danger in the spring grass? It is a simple sugar that is prevalent in our cool season grasses here called fructan. The products of photosynthesis are simple sugars and starch. When more sugars are produced that the plant needs for growth the excess is stored, or reserved, as carbohydrates for later use by the plant. This commonly occurs in the rapid growth early in the spring. These reserve carbohydrates contain high amounts of the sugar fructan, stored in the stem until needed by the plant. It has been proven that administering high concentrations of fructan to horses results in laminitis and is generally known to contribute to colic as well.
So how do you protect your horse from this? There are many methods, all of which are focused on reducing the amount of grass intake by the horse until their system is adapted to it, and the grass has gone through its early growth cycle and has reduced its fructans to a horse-safe level. One method is to use a grazing muzzle. Another method, and the one I prefer and have used, is to limit their time on the pasture in the first month or so. Start by turning them out only for 15 minutes on the first day, then add 15 minutes a day until you reach 4 to 5 hours of consecutive grazing. This ensures that not only will the health of the pasture be protected, your horse’s health will be protected too.
1. Kowalenko, C.G., S. Freyman, D.L. Bates, and N.E. Holbek. “An evaluation of the T-Sum method for efficient timing of spring nitrogen applications on forage production in south coastal British Columbia.” Can. J. Plant Sci. 69:1179-1192 (Oct. 1989)
This project has been funded wholly or in part by the United States Environmental Protection Agency under assistance agreements PC-01J18101 to the WA State Dept. of Ecology. The contents of this document do not necessarily reflect the views and policies of the Environmental Protection Agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use.
