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Worm Control News
April 2013

In This Issue
stool test
What does eggs per gram of feces really mean?
blade of grass with dew drop
One high-shedder horse can drop 6+ billion eggs that have the potential to become infective larvae in a pasture over a year's time. Each dew drop has a high concentration of larvae.
texting
What matters more, a friend's recommendation or an ad? Text it, tell it, post it, say it---to just one horse-owner friend---test before you deworm.
Doc Byrd
Price Increase Coming May 1
Hooved Animal Humane Society; Woodstock, Illinois; April 8
Dr. Byrd spoke at the Illinois Horse Fair in March.


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egg_distributionStrongyle Egg Distribution in Pastures

stool testWhat 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.

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 X 460 gms X 1000 (eggs per gm) = 18,400,000 eggs per day.
That's 6+ billion per year (18,400,000 eggs per day X 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 X 44000 = 418 eggs per day per square foot
  • 7 days X 418 eggs = 2926 eggs per week per square foot
  • 30 days X 418 eggs = 12,540 eggs per month per square foot
  • 365 days X 418 eggs = 152,570 eggs per year per square foot
  • 152,570 eggs per year X 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

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.

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billion
A Billion Reasons to Manage Your Pastures

blade of grass with dew drop One high-shedder horse can drop 6+ billion eggs that have the potential to become infective larvae in a pasture over a year's time. One low-shedder horse can drop 1.5+ billion eggs that have the potential to become infective larvae in a pasture over a year's time. All other shedders fall somewhere in between. Managing parasites in one horse starts with managing the parasite load of the herd, and managing the parasite load in the herd means managing the pastures.

How the Horse Gets Infected

Understanding how horses become infected is critical to understanding why and how pastures must be managed.

  • Most horses do not graze pastures evenly. Rather, they have areas where they eat the grass very short (lawns) and areas where they pass most of their feces (roughs). Consequently, the eggs are going to be concentrated in the roughs.
  • Most horses seem to avoid grazing in the roughs, allowing the grass to grow very lush and green in these areas because of the added nitrogen fertilizer.
  • Horses that are tempted to take just a few bites of this lush green grass while on their way to and from the bathroom area are likely to pick up large numbers of infective larvae, while other horses that resist the temptation do not become as heavily infected. This is one explanation as to why some horses on a pasture have very high egg count while others on the same pasture have very low egg count.
  • An infective larva generally travels no more 1.5 feet from the pile where it is passed as an egg by the horse, so there is a high concentration of eggs (potentially infective larvae) in the "rough" areas.
  • Infective larvae actually climb up the blades of grass (but generally no more than 3 inches high) when it is warm and moist in order to make themselves much more available to an unsuspecting horse passing by. Grass in a pasture that is not taller than 3 inches results in a very high concentration of infective larvae at the tips of the blades of grass. See a close-up photo that shows the infective larvae in a dew drop.
  • Horses grazing on a short pasture are more likely to be exposed to more infective larvae because the larvae crawl up the blade of grass only about 3 inches.

Other Factors Affecting Egg Distribution in Pastures

Two other factors that affect the distribution of worm eggs in a pasture are nature and man.

  • When it rains, eggs and larvae can be washed by the water over the pasture and be much more evenly distributed, thereby making it more difficult for horses to avoid them. We cannot control the rain but we may be able to control the drainage, thereby controlling the distribution.
  • The best practice for dragging or mowing of pastures is to first remove the piles of manure from the roughs once a week. Then drag or mow the pasture when the weather is hot and dry. Ideally, horses should be kept off freshly-mowed or dragged pastures for five days. Larvae need moisture to survive, and exposing them to the heat causes them to use up more of their stored energy and die. Infective-stage larvae cannot eat because of a special coating and must rely on energy stored from eating bacteria during the previous stage while in the pile of manure.

Recommended Reading

Understanding parasites, their life cycles, how they affect your horse and your pasture, and how to manage everything parasite-related can be challenging--there is a lot to learn. An excellent resource for anyone who owns or manages horses is the recently published Handbook of Equine Parasite Control by Craig R. Reinemeyer and Martin K. Nielsen. The book provides basic biology, general principles of parasite control, assessment tools, case studies and advice. It is available from several sources including Amazon and Barnes & Noble, in both print and e-book versions.

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recommendation
Your Recommendation Matters

textingThink about how much we rely on opinions and recommendations from our friends. We consider them more reliable than random ads that float across our screens. So it is with deworming. Share your opinion about the importance of testing before deworming. Recommend to your friends that they, too, should follow the new protocol of selective deworming---testing first and deworming only when necessary. The new protocol saves the aggravation of deworming an unwilling horse, minimizes exposure to unnecessary chemicals, and goes a long way toward helping to reduce the development of resistance parasites. Text it, tell it, post it, say it---spreading the word friend to friend is the most effective way of communicating and getting the word out.

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wordbyrd
Dr. John ByrdA Word from Dr. Byrd
Price Increase

Thank you for your loyal support over the years, we look forward to continuing to help you evaluate your horses' worm control program. However, due to the increases in labor, materials, and postage we must increase our prices. On May 1, 2013 the price will increase by $2 per sample. Any samples purchased before May 1 will be processed for the fee prior to May 1.

  • 1 sample: $20
  • 2-5 samples: $17/sample
  • 6 or more samples: $15/sample
Out and About

Spreading the word about testing before deworming, and educating horse owners about the growing resistance in parasites is a high priority for Horsemen's Laboratory.  Dr. Byrd enjoys meeting with groups and organizations to present "Are the Worms Winning?"--a discussion of the development of resistance in equine internal parasites. Meetings are  opportunities for Dr. Byrd to meet clients and horse owners face to face, and to answer any questions related to testing and deworming.  You can also contact Dr. Byrd if your organization is interested in hearing Dr. Byrd speak. Recent gatherings include:  

  • Hooved Animal Humane Society, Woodstock, Illinois on April 8
  • Illinois Horse Fair on March 1 and 2

 

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