Small Changes in Hay Have a Big Impact on Your Horse

102_2349 (Small)You just received a new load of hay in to your barn. It smells so good, and looks just like the last load you got from your regular supplier. But is it really the same? While it might be similar, growing and harvesting conditions vary with every single cutting, and that can have an impact on the nutrition contained in that sweet-smelling pile of bales in front of you.

Generally speaking, the differences aren’t going to be very big – but the next time your horse mysteriously starts losing weight, or losing muscle condition over his topline, you might want to question your hay supplier or get your hay tested.

For example – if your hay got rained on after it was cut, the rain can shatter the leaves, which is where much of the highly digestible protein is found in your hay.  And given how much of your horse’s daily diet is made up of hay, a small decrease in protein can have a big impact.  Let’s take a look at the math behind this:

A 1000 lb horse should eat 1.5-2.0% of its body weight per day in forage – that’s 15-20 lbs!

  • Hay A has 10% protein: 20 lbs of hay x 0.10 protein = 2 lbs of protein intake per day
  • Hay B has 8% protein: 20 lbs of hay x 0.08 protein = 1.6 lbs of protein intake per day

In this scenario, you’d have to feed an extra 5 lbs of Hay B per day to be feeding the same total protein as Hay A provides!

But how much difference does this really make, you ask? If your horse’s intake is already on the low end of protein requirements for his size and activity level, then a 2% drop in hay protein would potentially show up in 2 to 6 weeks. Over that time, all else being consistent, a decrease in general muscle tone, and muscling over the topline, will start to appear. Fortunately, it’s pretty easy to combat – in many cases, simply tossing in an extra flake or two of hay per day, or adding a ration balancer or 1 – 2 lbs of grain per day, at feeding time will combat the decreases – and what horse won’t love you for that?

Determining the Value of Rained-On Hay

George eating hay in his paddockRain occurring while cut hay is laying in the field causes both yield and quality losses that reduce the value of the crop as an animal feed and a marketable commodity.

Weather-induced losses are caused by:

  1. Prolonged plant respiration reducing soluble carbohydrates and overall energy content
  2. Leaching of soluble carbohydrates, protein, and certain minerals from the hay
  3. Leaf shattering and loss, removing the highly digestible and high protein portion of the forage
  4. Microbial activity metabolizing soluble carbohydrates and reducing energy content
  5. Color bleaching

How much does rainfall reduce dry matter yield?

Several researchers have studied the effects of rainfall on cut alfalfa. Wisconsin researchers measured dry matter losses of 22% when alfalfa was exposed to 1 inch of rain after 1 day of drying (curing). Similar hay dried without rain damage lost only 6.3% of the initial yield. Losses appear to be greatest after partial drying of the forage has occurred. In this same study, alfalfa exposed to 1.6 inches of rain over several days suffered a 44% loss in dry matter. Michigan researchers conducted several different studies to examine the effects of rainfall on field cured alfalfa. The first study reported maximum dry matter losses of 34%. In a second study, rainfall intensity was kept constant at about 0.7 inches but spread over periods of 1 to 7 hours. Dry matter losses ranged from 4 to 13%, with highest losses occurring when the rain was spread over a longer duration. Overall, dry matter losses were much lower in these experiments even though rainfall amounts were about 2 inches.

Other species have been studies as well. Yields losses of birdsfoot trefoil appear to be less than alfalfa, while red clover shows even less dry matter loss due to rain, and grasses suffer the least amount of dry matter losses. Dry matter losses are most crucial to the person responsible for baling the hay. Dry matter losses usually represent a significant decrease in income since less hay is available for baling, feeding, and selling.

How does rainfall reduce dry matter yield?

Three primary factors are involved in dry matter losses; leaching, respiration, and leaf loss. Leaching is the movement of cell solubles out of the plant. Components of the plant that are very water soluble are leached out of the forage and lost when rain occurs. Unfortunately, most of these compounds are those highly digested by the animal. They include such components as readily available carbohydrates and soluble nitrogen, minerals, and lipids. About one-half of the dry matter leached by rain is soluble carbohydrates.

Unlike other livestock, losses of soluble carbohydrate can be beneficial for some horses. Laminitis is a painful and debilitating disease of the horse hoof. Laminitis typically occurs during periods of increased or rapid intake of water soluble and nonstructural carbohydrates. In order to manage lamintic horses and reduced amounts of carbohydrates in harvested forage, horse owners have resorted to soaking hay. A number of research trials have confirmed removal of carbohydrates from hay by soaking in either 30 minutes of warm or 60 minutes in cold tap water. Soaking hay is a cumbersome, messy, and time consuming process. Purchasing rained-on hay with naturally low levels of carbohydrates is a possible alternative.

Respiration (breakdown of soluble carbohydrates by plant enzymes) occurs at nearly 2% dry matter per hour in fresh forage, and declines almost in proportion to the decrease in moisture content until the plant reaches approximately 60% moisture. Every time the forage is wetted by rain, respiration is either prolonged or begins again in cases where the cured forage was below 60% moisture. In either case, additional dry matter is lost.

There is some disagreement in the research literature regarding the amount of leaf loss that occurs in cut alfalfa as a direct result of rainfall. In Wisconsin studies, leaf loss ranged from 8 to greater than 20% as a percent of the initial forage dry matter when rainfall amounts were from 1 to 2.5 inches. In Michigan studies, direct leaf loss was much lower (0.5 to 4.2%). Perhaps the issue of leaf loss from rainfall is a mute point. Experience and common sense tell us that rain damaged alfalfa is more predisposed to leaf shatter after it dries, and rainfall often means additional raking and more lost leaves.

How does rainfall intensity and forage moisture affect losses?

Research is conclusive on these two points. Given the same amount of total rainfall, a low intensity rain will result in more leaching of soluble compounds than a high intensity rain. Also, as forage moisture content declines, it is more prone to dry matter loss from rain. In Wisconsin rainfall studies, the maximum loss in dry matter (54%) was a treatment where 2.5 inches of rain fell on hay that was nearly dried.

How does rainfall affect forage quality?

Perhaps nothing is more frustrating than to see excellent quality alfalfa turn into unsuitable feed with each passing rain and subsequent raking. Most rainfall studies are in agreement that wetting of field dried alfalfa has little impact on protein concentration. For rained-on hay, it is common to see relatively high protein values in comparison to fiber concentrations, unless significant leaf loss occurs. With the leaching of soluble carbohydrates, structural fibers (acid and neutral detergent fibers) comprise a greater percent of the forage dry matter. Depending on numerous factors, the digestibility of rained-on hay may decline from 6 to 40%. Changes in fiber components are thought to occur by indirect mechanisms, where the respiratory activity of microorganisms has a concentrating effect on fiber components by oxidizing carbohydrate components; additional fiber is not made during the wetting process.


Rained on hay can be a suitable forage, but quality depends on several factors. Forage quality tends to be retained if rain occurs soon after cutting when the forage has had minimal time to dry; the rainfall was a single event compared to a multiple day or drawn-out event; rainfall intensity was higher versus a longer, lower intensity event; and the forage has not been re-wetter numerous times. Rained on hay is actually beneficial for horses prone to laminitis and other metabolic disorders because of its reduced carbohydrate content. Analyzing forage for nutrient content is recommended, but can be especially useful when determining the quality of rained on hay.

This article is reprinted with permission from Dan Undersander, University of Wisconsin and Krishona Martinson, University of Minnesota. This and other horse nutrition articles can be found at

How to Help Your Horse Lose Weight

Is your horse an easy keeper? Or just need to shed a few pounds? This simple, short video gives you the first steps to follow to take weight off your horse.

For specific recommendations on feed selection, or advice on what to do if you’ve already taken the steps outlined in the video, leave your questions in the comments section!

Hauling Horses: Stay Back and Stay Safe!

Truck and Horse TrailerThe following situation comes from Joanna Russell, a Nutrena sales representative, who enjoys riding eventers and show jumpers.

My father grew up on a farm with cattle and horses, he could back a truck and loaded trailer well before he had a driver’s license. My mother was a registered nurse who took a few years off in her career to drive a semi. Driving a truck and horse trailer is a skill I started learning while I was fifteen and still had my learner’s permit. By the time I graduated high school, I didn’t think anything of loading a couple horses up and going to a friends to ride with them. By the time I graduated from college, I was used to driving my horses several hours at a time on both highways and back roads near home. I had even driven straight from Virginia to Kentucky with one of my mares in tow. And by the time I started working for Nutrena, I was a pretty confident driver, in my car or in a truck and trailer.

Then I had that confidence shaken.  Recently I hooked up my trailer to my truck (we call her Roxanne), and loaded up two of our geldings, Ty and Jack, for a clinic. I didn’t think anything of the three hour, all highway drive. There was light traffic, it was actually a very pleasant drive listening to my favorite CD and keeping an eye on my trailer. About an hour down the road traffic got a little heavier, so I was making sure to keep plenty of space between me and the car in front of me. I was being extra alert, thanks to a hands on defensive driving class I had taken through work. And of course, keeping the cardinal rules of hauling in mind: DO NOT slam your brakes and NEVER swerve.

I was in the passing lane as a car passed me on the right aggressively, so I slowed to give them more space. Suddenly, I saw brake lights and heard tires screeching, all the cars in front of me had their brakes locked up. I broke the Rule. I locked up the brakes on Roxanne and my trailer, I heard them both squealing and knew I wasn’t going to be able to get stopped in time. I knew I had an empty space to my right. I broke the second Rule. I swerved. Hard. I missed the cars in front of me by a hair, while I felt the horses scramble, the trailer shake, and felt cold fear and dread in the pit of my stomach.

There was plenty of space in the right lane, and whatever caused the slowdown was gone—traffic was back to normal speed. The shoulder was narrow, and an exit was only a mile up the road from me so I kept driving slowly with my flashers on. This was the longest moment of my life. Were the horses ok? What would I do if one of them had a broken leg? What about a heavily bleeding wound? I had very basic first aid supplies, but nothing like I feared I might need. I finally got to the exit and pulled in a truck stop. I ran back to the trailer, trying to keep from crying in fear until I knew…

One of the worst moments of fear and dread in my life was followed by the greatest sense of relief. Ty had fallen down, but only had a small scrape on his hock and on his cannon bone. Jack didn’t have a single mark. They were both wide eyed and shaking—not as bad as I was, though. I fed them treats until I stopped shaking and was comfortable to drive again. The rest of our drive was uneventful, and would have been pleasant, save the sick feeling lingering in my stomach.

I thought a 7 second following distance was enough. I was wrong. I will do everything in my power to keep a minimum of a 10 second following distance from now on, longer if possible. Always have a way out in mind, and use “what if” thinking (what if a car slams its brakes in front of me? Where do I go?)—it could save you lives and vet bills. You can bet I will be beefing up my equine first aid kit for my trailer! And a big take away for me: Not everyone will notice or care that you take longer to stop and have living creatures as your load, so plan accordingly.

I am thankful that my employer values my safety enough to have put me through driving training that at very least saved me from having to replace my truck, and at most, saved the lives of myself, my horses, and the drivers around me.

Confused by Carbs in Horse Feed?

There are lots of terms, and even more opinions, when it comes to carbohydrates in horse feed. Here, we break it down to the basics so you can have a foundation to understand what’s important to your horse!

understanding starch and sugar levels in horse feed

Click the image to enlarge.

Prebiotics and Probiotics in Horse Feed

Have you ever wondered if you should be using prebiotics or probiotics in your horse feed? The info below helps explain the benefits of both!

the effects of prebiotics and probiotics on horse digestion, prebiotics and probiotics in horse feed

Click the image to be able to zoom in.


Transitioning Your Horse to a New Feed

You may be thinking your horse is in need of a senior diet, or perhaps there is a new feed available that you believe is even better for your horse.  Maybe you are no longer happy with your current feed.  Or, your retailer no longer carries the product you were using.  Whatever the reason, switching your horse to a new feed is a change that requires care and know-how.

It’s important to transition your horse gradually over a 7 day period, gradually increasing the new feed and decreasing the old.  Throughout the process, you’ll want to watch your horse’s body condition and adjust feeding rates as needed.

Mixing with Current Feed – The Ideal Process

If still have some of your current feed, transition as follows:


Current Feed

New Feed

Day 1-2



Day 3-4



Day 5-6



Day 7


No Current Feed Available

Whether you just simply ran out, or your favorite feed has been discontinued or no longer carried by your retailer, sometimes you may not be able to mix their old and new feed slowly.  While not ideal, if no current feed is available, you can still safely transition to the new feed.

Because you don’t have any of the old feed to mix, you’ll want to reduce the total amount you feed your horse and gradually increase it again over 7 days, using the new feed.  It is a good idea to offer some extra hay or pasture-time during this transition, as well.  Feed your horse the new grain as follows:


% of recommend feeding rate of the new feed

Day 1-2


Day 3-4


Day 5-6


Day 7