Most people when asked what they feed their horses will give you the brand name of a bagged feed and the percent protein it contains. They may or may not know what type of hay they feed. Some even believe hay is nothing more than a fibrous filler.
Certainly very few people consider that hay is an important protein source. If a pregnant mare is being fed a moderate quality hay with 0.8 Mcal/lb calories and 8% protein, will she be getting less protein than a mare who gets her calories from both hay and 5 pounds/day of a 14% mare and foal feed? You may think the mare supplemented with the high protein feed would get more protein, but that’s not correct.
The reason is calories. If this mare needs 24 Mcal (megacalories) per day, she would require 30 pounds of hay. At 8%, that’s 2.4 pounds of protein. The mare and foal feed has 14% and 5 pounds of it would yield 0.7 lbs of protein. However, the calories are likely 3 times higher so she’s getting 12 Mcal from that 5 pounds, leaving only 12 more to come from the hay. At 0.8 Mcal/lb, that’s 15 pounds of hay which provides 1.2 pounds of protein for a total of 1.9 compared to the 2.4 she would get on a hay only diet. Even if you allow for the protein in the grain to be 20% more digestible, the total still won’t be as high on a hay only diet.
– By Dr. Eleanor Kellon, VMD and Staff Veterinary Specialist for Uckele Health & Nutrition