Why Feed More Than Hay? Part II: Vitamins and Minerals

Another common reason to supply your horse with more than pasture and/or hay is to enrich their diet with vitamins and minerals. Most, if not all, forages lack proper levels of certain trace minerals, so every single horse owner should find a way to offer these to their horse(s). There are many ways to do so- read on...

If you have not already read "Why Feed More Than Hay Part 1: Calories", HERE IS THE LINK.

At no time is vitamin and mineral nutrition more important than in pregnant mares and growing foals! In this article, we're going to explore how a local grass mix does or does not meet the vitamin and mineral requirements of this little guy- an adorable, 6 month old Paint weanling named Zephyr. Zephyr's owner contacted me before she had even brought him home wanting to know how to best meet his nutrient needs. She was new to baby horses and new to the temperate region of Montana. By taking steps to understand the local grass hay and pasture, she is now providing Zephyr with the right levels of critical nutrients for long term immune health, skeletal soundness, muscle development and more!

Zephyr was weaned in the late summer of 2021 and moved to his new home in Montana where he has companionship, plenty of fresh water, lots of room to run, and excellent nutrition provided by one simple product.

Understanding Zephyr's Primary Forage

Zephyr's owner, in an excellent move to take the guesswork out of his diet, sampled two lots of hay that she had acquired for the winter- a local 1st and 2nd cutting mixed meadow grass hay. This forage is perfectly meeting his caloric needs, so we can move immediately to the second most common reason to feed more than hay- vitamins and minerals. You're going to see the results of those forage tests below, and I will point out some of the mineral results. Instead of breaking down every single nutrient that Zephyr is known to require, I'm going to focus on the most important basics. For most young horses without unique special needs, covering these basics well will be more than adequate for ensuring good growth and health long term.

#1: The Calcium and Phosphorus Ratios

As we all know, the major minerals calcium and phosphorus are principle components of bone which is growing quickly in young horses. What you might not know is that the body requires a ratio of these minerals for proper assimilation; more phosphorus than calcium can cause disease and vice versa. A mature adult horse can handle ratios of calcium to phosphorus anywhere between 1.5:1 to 8:1, but it is thought that this window narrows in the young horse- ideally closer to 2:1 or 3:1.

First and foremost, we need to ensure that there is ALWAYS more calcium than phosphorus in the young horse diet. Therefore, one of the very first things that I check on a forage test is this ratio. As you can see below, the first cutting grass mix has a ratio of about 1.5:1. This is definitely borderline, so it's very important that we do not add any high phosphorus ingredients to Zephyr's diet such as beet pulp, grains, or rice bran. An easy way to balance this ratio better is to offer a small amount of alfalfa hay as part of the forage balance since alfalfa hays always have very high calcium to phosphorus ratios. We could also provide a ration balancer with added calcium.

1st Cutting Local Grass Hay Mix- Check calcium and phosphorus ratios

#2: Trace Minerals

The next thing to check for on this forage test are the levels of 3 VERY critical trace minerals; zinc, copper and selenium. Every horse owner needs to memorize these three trace minerals and ensure that they are being provided in the supplemental diet, because I have yet to come across a forage result that was adequate in all three. These three trace minerals are extremely important for the parts of the horse that we see- the skin, coat, and hooves. They are also very important for the systems that we can not see such as immunity and reproductive health.

I've provided a chart below that shows what 10 pounds of 2nd cutting grass hay is providing Zephry (roughly 2.2% of his current body weight in hay). *We are also assuming that he is getting a couple pounds per day from the pasture. Compared to his 6 month of age requirement (assuming 1,100 lb mature body weight) the hay is NOT providing anywhere near his zinc, copper or selenium levels. Therefore, it is absolutely critical that we provide him a daily supplement that provides these trace minerals. There are many ways to do this for Zephyr or any mature adult horse for that matter- jump past the chart and forage result to find out your options.

Note: Though selenium was not actively measured in this forage test, we can assume due to location and regional averages that there is little to no selenium. This may not be the case is in parts of Central USA and other hot spots of selenium around the country. Find out more at U.S. Geological Survey website.

Trace Mineral

Requirement in Milligrams (6 mn; mature weight of 1,100 lbs)

Contained in 10 lbs of 2nd Cutting Tested Grass Hay (mg)

Difference (mg)




146 mg (32% of req't)




34 mg (37% of req't)



Unknown- assumed zero

-0.54 mg

#3: Protein

A quick note about this forage test result. At 8.7% and 10.4% crude protein, I believe these forages to be inadequate for a young growing horse. A crude protein report is just that- CRUDE. We do not know the individual amino acid content and quality, but with relatively low crude protein levels, low digestibility of first cutting, and Zephyr's future in mind, I would highly suggest a ration balancer for this young horse (any brand). In my opinion, a simple vitamin and mineral product will not suffice.

2nd Cutting Local Grass Hay Mix- Check Trace Mineral & Protein Levels


There are several ways to meet a horse's trace mineral requirements. What you choose will depend on your horse's requirement, management situation, your budget, and product availability more than anything else. There is a TREMENDOUS amount of diversity out on the marketplace too including various nutrient levels, sources of nutrients (i.e. organic vs inorganic compounds), and serving sizes. If you need help weeding through all t