Strongyle egg distribution in pastures: What does eggs per gram of feces really mean? That’s a question we are often asked here at Horsemen’s Laboratory.
When we say a horse is passing 1000 strongyle eggs/gm of feces a day, that gives us an estimate of how quickly and thoroughly a horse is contaminating its environment—the pasture in this case—with eggs that could become infective larvae for pasture mates.
Horse pastures: Source of infective larvae
The sheer number of strongyle eggs that could become infective has serious implications for horse pasture management whether a boarding barn or private barn with pasture turnout.
Do the Math: The best way to explain how infective a pasture could become is with an example. The setting for this example is based on one horse (a high shedder) on one acre (44,000 sq. ft.) of pasture 24 hours a day and passing a conservative amount of stool (40 lbs.) containing 1000 strongyle eggs/gm. of feces per day.
We’ll use the numbers below in our formulas:
1 lb = (approximately) 460 gm
1 acre = 44,000 square feet (sq. ft.)
1 sq. ft. = 144 square inches (sq. in.)
1 square inch is slightly larger than a postage stamp
The Impact of Just One Horse on a Pasture
So, from one high-shedder horse there could be:
40 lbs ´ 460 gms ´ 1000 (eggs per gm) = 18,400,000 eggs per day.
That’s 6+ billion per year (18,400,000 eggs per day ´ 365)
Combine those numbers with pasture area to see how heavily infested a pasture could become from just one high-shedder horse over the course of a year.
- 18,400,000 ¸ 44000 = 418 eggs per day per square foot
- 7 days ´ 418 eggs = 2926 eggs per week per square foot
- 30 days ´ 418 eggs = 12,540 eggs per month per square foot
- 365 days ´ 418 eggs = 152,570 eggs per year per square foot
- 152,570 eggs per year ¸ 144 (square inches per square foot) = 1060 eggs per square inch per year—an area just slightly larger than a postage stamp
Shedding classification is as follows and will affect the number of eggs in the formulas above.
- Low shedders: 0–200 eggs/gm
- Medium shedders: 200–500 eggs/gm
- High shedders: 500 or more eggs/gm resulting in 0000 eggs per square inch per year
No matter how you look at it, that’s an astounding number of eggs per horse—even when you take into consideration shedding status. The sheer number of eggs that could become infective has serious implications for pasture management whether you are a boarding barn or private barn and offer pasture turnout.
Horsemen’s Laboratory owner Dr. John Byrd has extensive experience with racing and breeding horses and oversees Westbrook Boarding Stable. He created Horsemen's Laboratory in 1992 so that horse owners could better evaluate their worm control programs and make informed decisions about deworming their horses. Dr. Byrd is a member of:
- American Association of Equine Practitioners (AAEP)
- American Veterinary Association
- American Association of Veterinary Parasitologists
- ·American Quarter Horse Association
Learn more about Horsemen’s Laboratory and parasites, to sign up for the monthly newsletter, and to order testing kits. You can also order kits by calling 1-800-544-0599.
Learn more about Horse Parasites