Grass is similar in nutritional content to hay, except it contains 80% water.

The major difference between feeds suggested for use in broodmares and those for other classes of horses is a higher protein level. For broodmares, 14 to 16% is the usual, while 10 to 12% protein is the norm for other feeds. Pregnant and lactating mares do need a lot more protein but, frankly, even this level might not get the job done well enough.

The difference between a 10% and 16% feed in terms of protein is only 27.2 grams/lb., while an 1,100-lb. mare in heavy lactation needs about 770 grams more protein in her daily diet. Look at what happens with a 1,100-lb. mare on a hay, then hay and grain pregnancy diet, when switched to a broodmare feed after she foals.

Pregnancy: 22 lbs./day of 8% protein hay =  800 grams of protein/day (adequate through the ninth month of pregnancy); 20 lbs./day of 8% protein hay + 2.2 lbs./day of 10% protein feed = 871 grams of protein/day (adequate up to foaling)

Lactating: 25 lbs./day of 8% protein hay + 6 lbs. 16% protein feed = 1,345 grams of protein/day (about 80 grams short). Since many of the grass hays fall below 8% protein, this could be even worse.

Put It To Use

Even 16% protein in feeds may leave the mare short of protein during lactation. Adding 1 lb./day of 50:50 alfalfa pellets and soybean meal to her diet will bridge the gap. Other options are ½ lb./day of soybean meal or sunflower meal. Feeds labeled for performance horses may do just as good a job as those for broodmares. Check your labels. For lactating broodmares being fed at the lower end of feeding recommendations (about 6 lbs./day of grain), choose a feed with 16% protein, 0.75% lysine, minimums of 0.75% calcium, 0.5% phosphorus, 50 ppm copper, 150 ppm zinc, 120 ppm manganese. Additional vitamin E, selenium and iodine (iodized table salt a good source) will often be needed. Don’t combine high potency supplements with fortified grains if you are feeding at least the minimum recommended amount (usually 6 lbs./day).

Fortunately, nature provides a natural protein boost in the form of young pastures, where 20% protein is common. However, for the mare with little or no pasture access, you’ll need to feed more protein.

Since the grains have a calorie value at least twice as high as most hays, it won’t do any good to feed more grain because you would have to cut back the hay and 2 lbs. of an 8% protein hay has the same protein content as 1 lb. of a 16% protein grain.

Possible solutions:

Provide 1 to 2 lbs./day of a 30% protein supplement. This will cover the protein needs, but since these products are highly mineral-supplemented you’ll end up overdoing it on the mineral front.

You could solve the problem by adding a ½ lb./day of soybean (Calcium:phosphorus = 1:2.46) or sunflower (Ca:P = 1:2.24) seed meal, or Uckele’s Amino Fac 41 (Ca:P = 1:2.25), but this could upset your mineral balances.

Another option would be a 50:50 mix of alfalfa pellets and soybean meal. This will have 31.5 to 35% protein on the average and about 50% more calories than average grass hays, so you can feed more and will provide more energy in the form of digestible fiber than with high-starch grains. 1 lb./day of the 50:50 soybean meal and alfalfa pellets has a balanced calcium:phophorus ratio, makes up the protein deficit without overdoing other minerals and costs considerably less.

Next to consider is lysine intake. Lysine is an essential amino acid that is the most essential for normal growth and development, and the only one for which precise requirements are known. A mare in the last trimester of pregnancy, who was on an adequately balanced maintenance diet before pregnancy with at least 0.3% lysine has a relatively small requirement for additional lysine. This can be easily met by feeding her 1 to 1.5 lbs./day minimum of any commercial feed with a guaranteed lysine content of at least 0.6%.

As our feed chart on page 16 shows, even “regular” feeds like Triple Crown 10 or Nutrena Compete have sufficient lysine so there’s no point in switching to a mare feed.

The lactating mare has a more sizeable deficit, even when increasing her feed by 70% and starting from a good base maintenance diet as just described. If you feed this mare 6 lbs./day of a 0.6% lysine mare feed, she’ll still be a little short. You’ll need a feed with 0.7 to 0.75% lysine to provide enough. The 50:50 soybean meal and alfalfa mixture is also rich in lysine, about 1.8%.

Protein Amounts In Feeds
10% protein = 45.4 grams/lb. 12% protein =  54.5 grams/lb. 14% protein =  63.5 grams/lb. 16% protein =  72.6 grams/lb. Soybean meal = 204 grams/lb. Sunflower seed meal (no hulls) = 204 grams/lb. Alfalfa = 63.5 to 80 grams/lb. Flaxseed meal = 90 grams/lb.

What About Minerals?
Minerals are where we really count on the mare feeds to get the job done. Any feed, whether labeled specifically for mares or not, will  meet the trace mineral requirements if it contains at least 50 ppm of copper, 150 ppm zinc and 120 ppm manganese, when fed at 6 lbs./day with 25 lbs. of hay that has been appropriately balanced. It’s much more difficult to say with certainty if they are adequate for calcium and phosphorus.

For calcium for example, grass hays may be as low as 0.3% calcium, or as high as 0.6%. Phosphorus also has a wide range. Six pounds of a 0.6% calcium feed provides 16 grams of calcium compared to a requirement during lactation of 56 grams, which could leave the mare a bit short in calcium during lactation. The mare in late pregnancy could also need more calcium than that provided by a small amount of a 0.6% calcium feed. We’d recommend making sure the calcium level in a feed being used for pregnant or lactating mares be at least 0.75% calcium, 0.5% phosphorus. 

At 0.6 ppm selenium, 6 lbs. will provide 1.6 mg of selenium. This too may be a little light, so consider adding an addition 1 mg/day, or having the mare’s selenium blood level checked and supplementing accordingly. Many of these feeds also contain vitamin E, but it may not be stable for long in a feed. Supplementing pregnant and lactating mares with a separate vitamin E supplement is advisable. 

Bottom Line
If your hay has 8% or less protein, low end for calcium (i.e., around 0.3%), and you’re going to be feeding the usually recommended low-end 6 lbs./day of feed (about 2 lbs./day in late pregnancy), you’ll need a feed that contains the minimal upper ends of nutrients:

16% protein

0.75% lysine

0.75% calcium

0.5% phosphorus

50 ppm copper

150 ppm zinc

120 ppm manganese.

Nutrena Youth, Nutrena Develop, Buckeye GrassPlus Developer and TDI 16 meet those high-end requirements, and we especially like that the TDI 16 specified manganese content. When fed at the 6 lbs./day level, even these feeds could stand a bit of a protein and lysine boost from a pound or so of a 50:50 mixture of soybean meal and alfalfa.

For hay with 8% protein or higher, calcium at least 0.5%,  you can get good results with either a 14% or 16% protein feed with a calcium minimum of  0.6%. Note that many of the feeds listed here that are normally thought of as performance horse feeds will work just as well as a mare feed. If you go with a 14% protein feed and have a 8% protein hay, you’ll need another 54 grams of protein on top of the 80 already mentioned when feeding 6 lbs/day of this feed.

Warning: The recommendations used in this article refer to an 1,100-lb. mare, whose base diet (both hay and grain) when not pregnant was known to be balanced and to meet the minimum National Reseach Council (NRC) requirements for protein, vitamins and minerals. If the base diet is not balanced or adequate, that will change her requirements.