How to Grow Worms (or Not)
Dr. Steve Hart
Extension Goat Specialist
Not only will rotation grazing help with worms, it will increase forage production
and utilization, enabling the producer to run more animals per acre.
This month’s timely topic is about planning grazing as part of your parasite control program for the year. With proper planning, you can reduce worm problems and losses from worms. Most of the management to prevent worms revolves around grazing management.
If you live in a humid area (greater than 25” of rain per year) you cannot effectively control worms unless you have multiple pastures. Somehow, you need to divide your pasture up to multiple grazing areas. Six is the minimum, more pastures are better. Some research has shown that having 4 pastures and spending a week in each one does not help with parasite problems over grazing one large pasture. Not only will rotation grazing help with worms, it will increase forage production and utilization, enabling the producer to run more animals per acre.
Pastures may be divided up economically by electric fence. Properly managed electric fence will work for sheep and goats and is more economic than permanent fence, but electric fence does not work for all managers. Divide your pastures up into smaller pastures. Your local natural Resources Conservation Service agency can help you design a fence layout to divide pastures and in some cases pay part of the cost of fencing.
Ideally, animals can graze a pasture until infective larvae appear and then animals need to be moved to the next pasture. The length of time for infective larvae to appear depends on temperature and moisture. Ideal hatch temperature for most larva species is somewhere around 85 degrees. Hotter than this may increase hatch rate, but decrease hatch percentage. Cooler than this will increase the time for worm eggs to hatch and develop to infective larvae. However, larvae will not escape from the fecal pellet unless you have several days of heavy dew or rain to soften the crust on the fecal pellet to enable the larvae to float out of the pellet and up on forage.
You can safely graze animals until it rains if no rain has occurred in the last two weeks. The time to develop to an infective larvae may be 4 days in the tropics, 5-6 days in the southern US and two to three weeks in the northern US. If you only graze pastures a day less than this and move them to the next pasture, your animals should avoid being exposed to infective larvae.
Another important grazing factor is the length of residual: how tall the grass is when you finish grazing an area. Infective larvae are concentrated in the lower 3-4 inches of forage. Leave a pasture residue of about 4 to 5 inches long so animals avoid picking up infective larvae while grazing the pasture. Checking FAMACHA© scores regularly and deworming as needed will reduce pasture contamination with infective larvae since those animals with high fecal egg counts will be dewormed and produce only a low level of fecal eggs (if your dewormer was effective).
OK. The next problem is how long before the infective larvae on pasture die and animals can safely graze these pastures again? It depends, mostly on temperature. The infective larvae cannot eat and must live on the “fat” on their back. When the fat runs out, they die of starvation. How long does the fat last? It depends on temperature. The larvae, being cold blooded; their metabolism is slow when it is cool and fast when it is hot.
In the tropics, one study showed that infective larvae only survive on pasture about 30 days. In the southern US, survival is probably about 42 days; 60 days or longer in Northern US. If you have native grasses or browse, you can rest the pasture for 60 days without a reduction in forage quality. If you have improved grasses (such as bermudagrass, Orchardgrass, Timothy, or Fescue), forage quality will deteriorate after about three to five weeks growth.
What options are available? One option is to make hay, which cleans the pastures up. However, most small ruminant producers are too small of scale to do this. Another option is to graze another species of animals, such as cattle or horses which do not share the same parasites as small ruminants. They act as giant vacuum cleaners, consuming forage with the infective larvae which die in their manure. If you don’t have these other species, sometimes, you can work out an agreement with a neighbor who will loan you these species to clean your pasture up.
Another option may be to mow the pasture as recommended by Cornell University. The recommendation is to mow pastures closely a few days after grazing when it is going to be a sunny, hot day. This will expose the larvae to sunlight and hasten their death. It will also slow the pasture growth enabling it to remain in a vegetative stage of growth despite a long rest period while waiting for the larvae to die.
Browse and tannin-containing species also help to control worms. With browse, animals are not eating close to the ground and therefore pick up fewer infective larvae. In addition, browse often has a high protein and mineral content which helps to support the immune response. Some tannins such as those in Sericea lespedeza, sainfoin and chickory have been shown to reduce fecal egg counts and egg hatch and larval development. Grazing pastures with some of these forage species can be beneficial to controlling worms.
Doing fecal egg counts at two to four week intervals from a few animals will provide feedback on how well your pasture management is going. Knowing the biology of the parasite will enable you to make changes to your grazing plan for the next year.