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Ask the Nutritionist: Dr. Getty's Forum for Equine Nutrition

   Welcome to my forum. 

Here you will find more than 6 years of questions and my answers. It is searchable and offers a great deal of information. 

Currently, I am discontinuing new questions. This may change in the future, but in the meantime, please know that It has been a true pleasure serving you. 

Take a look at my Nutrition Library and Tips of the Month for a variety of answers on selected topics. Be sure to sign up for my monthly e-newsletter, Forage for Thought

I also have a growing number of recordings on "Teleseminars on Nutrition Topics that Concern You" as well as the new, Spotlight on Equine Nutrition Series -- printed versions of favorite teleseminars.

And finally, look for my articles in a variety of local publications and online newsletters, as well as the Horse Journal, where I am the Contributing Nutrition Editor.  

 

All the best,

 Dr. Getty 

 



Ask the Nutritionist: Dr. Getty's Forum for Equine Nutrition
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Re: Phosphorus and pregnant mare

A tag along question: Since this post I have been trying to educate myself about the relationships among minerals. I just read where excess calcium can interfere with the absorption of zinc. If this is true, should I be concerned with the excess calcium in this mare's diet? Thank you.

Where are you from? North Florida

Re: Phosphorus and pregnant mare

Sorry to keep adding to this post, but the mare is about to enter her 9th month, and according to NRC, Ca and P requirements are going to change. She still will be getting enough calcium. But phosphorus requirements are now 21g x 150%= 31.5 grams, or 12.5 grams more than she is getting in her diet. Appears to me like a phosphorus supplement is now needed.

What do you suggest, wheat/rice bran or a commercial supplement?

Thanks

Where are you from? North Florida

Re: Phosphorus and pregnant mare

Hi Billy,

Thank you for your patience during the holiday season.

Exact balancing of calcium and phosphorus is tricky since not all of the calcium in the diet is well absorbed. Young horses may absorb around 70% but as horses age, their calcium absorption rate declines (see page 71 of Nutrient Requirements of Horses, 6th edition).

In addition to age, the amount of phytate (found in forages) and oxalates in the diet can further decrease calcium absorption.

And additionally, as phosphorus increases, calcium absorption decreases.

For this reason, I am hesitant to supplement phosphorus. The risk of adding too much phophorus in relation to the actual amount of Calcium reaching the cells, is too high.

During the last three months of gestation, calcium requirements increase, as you mentioned. Use an absorption efficiency of 50% when doing your calculations. According to the NRC, the optimal dietary calcium concentration is 0.55% of the diet. You can mix grass and legume hays together to come up with an amount close to this percentage.

Regarding phosphorus, it, too, is poorly absorbed. But, as long as it is adequate in relation to calcium, your mare will be fine. The goal, as you know, is for phosphorus to not exceed calcium. Adding rice bran, for example, can be done, but I would opt for a calcium to phosphorus ratio between 2.5 and 3.0 to 1. Take into consideration all of the grain she is getting, as well, since cereal grains are high in phosphorus.

Regarding interactions with zinc... yes, too much calcium can interfere with zinc absorption, and vice versa. This is why I prefer to feed whole feedstuffs, rather than supplement individual minerals.

Bottom line... I would improve the phosphorus content through bran and/or grain supplementation only to the extent that the requirement is met. As long as phosphorus is adequate, your mare can safely tolerate 5 or even 6 times more calcium.

Happy Foaling! And a very Happy New Year,

Dr. Getty
Author of Feed Your Horse Like A Horse

Billy Blackman
Sorry to keep adding to this post, but the mare is about to enter her 9th month, and according to NRC, Ca and P requirements are going to change. She still will be getting enough calcium. But phosphorus requirements are now 21g x 150%= 31.5 grams, or 12.5 grams more than she is getting in her diet. Appears to me like a phosphorus supplement is now needed.

What do you suggest, wheat/rice bran or a commercial supplement?

Thanks

Where are you from? Bayfield, CO