A: Kudos to you for wanting to feed your horses in a way that aligns more closely with their digestive anatomy and physiology. It can be a little scary to watch your horses gorge day after day. The majority of horses do self-regulate after several weeks. Some do so more quickly and some take longer. Of course, there are always the exceptions to the rule who just do not self-regulate.
It is important to pay attention to your horse’s body condition and weight. I would recommend performing a condition score and weight estimate on your horses every two weeks so that you can determine objectively if any are gaining weight. Some horses might be gorging and yet their weight might not change. Excessive weight gain, especially in breeds at risk of metabolic disorders, is always a concern no matter how hay is fed. Pay particular attention to the formation of neck crest fat.
Some things that might help this transition include:
Consider hay quality and getting it tested
Ideally when free feeding hay you want a hay with low in nonstructural carbohydrates (NSC, or starch and water soluble carbohydrates less than 12% on a dry matter basis) and on the lower end for calories (under 1 Mcal per pound better yet closer to 0.8 to 0.9 Mcal/lb). This means that, despite having free access to the hay, the hay being fed has less nutritional value than a forage with higher NSC and calorie content. This will help prevent your horses from gaining weight while eating free choice.
The acid detergent content (ADF) will help indicate the amount of the hay that’s indigestible. Generally staying with an ADF between 35-40% tends to be good options for horses eating free choice. A lower ADF is preferable for competition horses and breeding/young stock. Be careful not to get hay that is so indigestible that there’s a risk that it might cause impaction colic due to poor digestibility. If testing hay is not feasible look for bales that have a lower leaf to stem ratio, because hay with more stem generally the hay is lower in NSC and calories.
Typically alfalfa is not recommended as a hay for free feeding due to its higher calorie content. As long as you do not experience weight gain I think it is fine to continue the alfalfa. However, if weight gain starts to creep in consider dropping the alfalfa hay or at least reducing the amount fed. If you’d like to feed some alfalfa for example as a source of higher quality protein or to mitigate ulcer risk, then perhaps switch to pellets that can be more carefully weighed out.
Understanding that horses might appear “fat” when they aren’t
Increased forage consumption leads to greater gut fill and more indigestible fiber throughout the digestive tract. This can lead to an increase in the horse’s barrel and can be misinterpreted as the horse getting fat when fat levels have not changed. Additionally, fiber encourages water consumption and holds more water in the digestive tract, adding the appearance of bulk. If in doubt use a weight tape and body score condition your horse every other week to keep track of any weight fluctuations. Again I would be particularly concerned a horse experienced an increase of crest fat, which could indicate metabolic function issues.
If you are currently feeding hay completely loose as well as free choice, using a slow feeder might be a good idea. These come in many forms from rigid plastic feeders to small holed nets. The benefit of these systems is that they help slow consumption and regulate intake. They also save on a great amount of waste. Another benefit of utilizing some kind of slow feeder, especially nets, is that you can place them strategically around the horse’s living space encouraging movement. The more the horses move the more calories they burn and movement is good for encouraging the passage of feed through the digestive tract. Nets that you can fit an entire bale in are available but smaller nets make for easier distribution.
Ensure the hay does not run out
Initially the rapid consumption of hay when fed free choice is due to the habit of meal feeding. If feed runs out once switched to free feeding the horse is going to experience the lack of hay as a break down in the feeding system and could become stressed and as a result go back to rapid consumption. Therefore it’s vital, especially for the first weeks, to ensure that hay does not run out day or night. When using nets I like to see a soccer ball sized amount of hay left in the net when I next come to feed. This tells me that the horse had access to hay that could have been consumed if desired but that the choice was made not to eat it. You mention that they are pigging out during the day. Does this mean that they do not have free access to hay at night? If so, then the gap in hay availability might be why they have not yet self-regulated their intake.
Pay attention to behavior
Take note of your horse’s behavior at feeding time. Are they waiting for you to come and feed and eager to get eating or are they pretty nonchalant about feed arrival? The latter typically suggests that they are moving towards regulation of intake. They are realizing that hay is always available so there is no reason to stand anxiously awaiting the next meal arrival. I have had clients also report horses that used to be banging at the stable door each morning become far more relaxed around feed time and interestingly they also observed changes in personality under saddle. A greater willingness to work and the sense that the horse was less tense and on edge. While anecdotal it does make sense that being generally more relaxed about life could impact behavior when ridden.
Make sure that you have plenty of fresh clean water available. Increased forage intake increases water consumption, so it’s very important to make a constant supply of fresh clean water available at all times.
To ease your mind weigh what they are eating—If you’re using smaller nets this is pretty easy. Weigh the nets when full and then even if not empty weigh them again before refilling and calculate the difference to determine how much was consumed. If there are multiple horses eating from the same nets average the consumption across the number of horses to estimate intake per horse. Then compare this to the average weight of the horses. I’ve had clients do this and what has been interesting is that the horses have all consumed about 2% of their body weight per day. This is right around the amount of voluntary forage consumed by the horses in numerous grazing studies quoted in the National Research Council nutrient requirements of horses.
Be sure to provide necessary micronutrients—As you would when feeding limited forage you need to ensure a quality course of additional trace minerals and vitamins. When feeding the hay with a slightly lower nutritional value as recommended above insuring a source of quality protein in the ration is a good idea. This is because the more mature hays that have the lower NSC and calorie levels also tend to have lower crude protein contents. For this reason I recommend feeding a high-protein ration balancer as a way of not only meeting the mineral and vitamin requirements but also of providing the necessary quality protein.
In summary I would focus attention less on the actual act of hay consumption and rather on the body condition and weight of the horses. Some moderate weight gain is to be expected initially; however, if weight gain continues unchecked this would be an indicator that free choice hay is not a viable option for that particular horse.