Minerals for Horses: Ca and P: Putting It All Together

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Written By Dr. Kris Hiney


Greetings again fellow horse owners! Hopefully everyone has had a chance over the last few months to start thinking about mineral requirements for horses in mathematical terms. To review, we have discussed the importance of Ca and P, especially in consideration of broodmares and young, growing horses. We have worked on calculating the Ca to P ratio you are providing in your diet, as well as comparing the total amount fed to the animal’s requirements. The suggested daily intake of Ca and P has been provided in tabular form, as well as some common feedstuffs’ concentration of these two minerals. Most importantly, we have worked out the math step-by-step, in order to allow you to really take a close look at your feeding program. This month we will more directly address the idea of feeding young horses properly.

Let’s talk babies!Again, review the last two articles which provided the amount of Ca and P that is needed by young growing horses. Compared to maintenance horses and exercising horses, the amount they need appears relatively small. But remember, their body size is also small, as well as the amount they can consume in one day! I think it is worthwhile to spend some more time specifically on this important class of horses. One of the difficulties in determining your young horse’s requirements is that they are usually listed according to their mature weight. Certainly that is how I presented this material in the last two months. But in order to help you out, the following table provides information on how much your young horse should weigh at various ages. This, of course is still according to their expected mature weight, which is at best an educated guess (See Minerals for Horses: Calcium). It is always important to monitor your foal’s weight gain, and determine if they are gaining excessive body fat. In addition, observe their joints carefully. Swollen and perhaps painful joints may indicate too rapid of a growth rate. For long term soundness, this is important to avoid.Table 1. Expected weights of young horses predicted by their expected mature weight. Note: these values would be typical of foals gaining weight at a moderate rate of growth. 

Mature Weight (lbs) 4 month 6 month 8 month 10 month 12 month 14 month 16 month 18 month 20 month
900 302 392 461 524 578 623 663 697 726
1000 336 432 513 582 642 692 737 775 806
1100 370 475 564 641 706 764 811 853 887
1200 403 571 614 699 771 831 885 930 968
1300 437 560 668 757 836 900 959 1004 1048
How much will Junior eat?Intake in young horses is varied, and certainly will be different due to feed availability, palatability of the feed, and competition between herd members. However, on average, young horses will eat between 2 and 3% of their body weight on a dry matter basis. So let’s assume we are feeding a 4 month old foal who will mature to 1100 lbs 2.5% of its body weight per day. We will feed him a mixed grass and legume hay that contain 1.09% Ca and 0.35% P. Now, let’s see if we are meeting his Ca and P requirements.The foal is currently 370 lbs. If he consumes 2.5% of his body weight that will be 9.25 lbs of hay per day. Let’s convert now to kg, remembering to divide by 2.24. Thus the foal is eating 4.1 kg of hay per day. Calculating by the percentage of Ca and P, this hay will provide 45 grams of Ca per day and 14 grams of P. Need a review? Revisit Part 2 in our series of minerals for horses. Now look at your tables. Our foal is meeting his Ca requirements but is 12 grams short of P. So what should we do? This is a situation where concentrate feeding is clearly warranted. So let’s select a suitable feed for our baby and recalculate. 

We will adjust our feeding scheme to feeding our foal 1.5 % of his body wt as forage and 1% as concentrate. Feeding such a diet that s approximately 65% forage and 35% concentrate is fairly typical for young horses. Previously young horses were believed to need a much higher proportion of grains in the diet, but recent research has shed light on better strategies for feeding young horses. This diet will now provide 2.5 kg of hay and 1.7 kg of concentrate. The feed we select to use is designed for young horses and broodmares. It contains 1% Ca and 0.55% P. When we recalculate, this diet now provides 27 g of Ca and 9 g of P from the hay, and 17 g of Ca and 9 g of P from the concentrate. Added together, the foal is now receiving 44 g of Ca and 18 g of P. He is still a little bit shy in phosphorous, but I don’t want to add more grain to the diet. Alternatively, I could select a feed that provides slightly more P.

I decide to use a select a new feed which contains a higher percentage P at 0.7% while the Ca content remains the same. All figures would remain the same with the exception of the P contribution from the new feed is 12 g of P. We have reached our goal of feeding our new guy a balanced ration (at least in terms of Ca and P)!

Now, for the sake of argument, let’s try to formulate a new ration that relies on slightly less grain for our growing foal. We will feed 2 % of his body weight in hay, 0.5% in concentrate and add a mineral supplement. The mineral supplement I chose has a concentration of 13% Ca and 12% P. It is designed to be fed at the rate of 2-4 oz per day. We will feed our baby 2 oz of the supplement per day.

Hay : 3.3 kg/day (2% of his body wt)
3.3 kg x 1.09% = 36 g Ca
3.3 kg x .35% = 12 g p

Grain: 0.8 kg (0.5% of his body wt)
0.8 kg x 1% = 8 g Ca
0.8 kg x 0.55% = 4.4 g P

Mineral supplement: 2 oz per day
Note: There are 28.35 g per oz. Therefore this colt will receive 56.7 g of supplement
56.7 g x 13% = 7.4 g Ca
56.7 g x 12% = 6.8 g P

All together the diet now provides 51 g of Ca and 23 g of P. This meets both his Ca and P requirements while allowing you to feed a more forage based diet. Now, which should you do? Well, that’s a topic for an entirely new discussion!

Next month we will continue on with minerals, but discuss one of the most confusing, miscalculated minerals there is – selenium. Until then, happy horse feeding!


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