How many goats can I stock per acre of pasture? I’ve increased my pasture rotation to 30 days, how much will this reduce the parasite problem with my sheep?
These are a couple of questions that I have been asked recently and each can be used to illustrate some basic differences in pasture management with small ruminants as compared to cattle.
If stocking rate was the primary consideration in determining animal numbers for a small ruminant enterprise I might say that five to six head can be stocked per acre on a average to better than average pasture.
However, pasture quality is not the primary consideration in determining the stocking rate for small ruminants, or at least it isn’t if the owner is planning on being in business for the long term.
No, it is not pasture quality, but rather internal parasites that determine the answer.
The parasite of concern is the Haemonchus contortus, better known as the barber pole worm. The barber pole worm is a blood sucking parasite with an extremely high reproductive rate, a quick life cycle and an ability to survive on pasture paddocks for a long period of time.
Under ideal conditions of moderate to high temperatures and moisture, the entire life cycle can be completed in as little as 23 days. We often have those ideal conditions from late June through August in Ohio.
Ohio research: Over 103 million eggs were being deposited on pasture daily; that figures out to about 2.25 million eggs shed per sheep per day.
Thousands of eggs
The adult Haemonchus contortus parasite can lay up to 5,000 eggs per day, which in a grazing operation are shed on to the pasture where the sheep or goats are grazing. Research and farm trials in Ohio have demonstrated the tremendous reproductive capacity of this parasite.
I know of one Ohio study that estimated total egg output per day for a flock of 46 sheep. Over 103 million eggs were being deposited on pasture daily, that figures out to about 2.25 million eggs shed per sheep per day!
After the eggs are shed in the feces on to the pastures, the eggs hatch and pass through an L1 and L2 non-infective larvae stage. Once the larva develops into an L3 stage, it begins to move up and down grass blades each day in a film of moisture.
Our summer dews provide all the moisture that is needed. L3 larvae on grass blades are consumed by grazing sheep. Once inside the sheep, the larvae continue to develop to an L4 stage and then on to the adult stage that attaches to the small intestine. Adults start sucking blood and laying eggs.
Under optimum conditions, the period between the egg being deposited on the pasture and development into the infective L3 larvae may be as quick as four days.
The reality is that summer pastures contain about 95 percent of the total Haemonchus contortus parasite numbers, with only about 5 percent of the total carried inside the animal.
Pastures can quickly become contaminated to the point where every mouthful of grass ingested by a sheep or goat contains hundreds or thousands of infective larvae.
Small ruminant survival depends upon some combination of factors that include an immune system response that allows animals to resist the parasites and greatly decrease or stop egg laying, resilience or the ability to tolerate a relatively high parasite number, and/or effective anthelmintics, which are chemicals either synthetic or botanical in nature that kill off the parasites inside the animal.
The bad news for graziers is that lactating ewes and does have a suppressed immune system and are susceptible to Haemonchus contortus infections, and young lambs and kids do not begin to develop any immune response until about six-eight months of age so they are extremely susceptible and vulnerable to Haemonchus contortus infections.
That leaves anthelmintics. This used to be the standard protocol to protect lactating ewes and does as well as young lambs and kids from parasite infections. Administer an anthelmintic, usually a chemical dewormer.
The recommendation generally was to de-worm about every 21 to 23 days. This strategy works as long as the chemical de-wormer is effective.
The bad news continues as there is documented proof of widespread Haemonchus contortus resistance to every class of chemical de-wormer on the market. There does not appear to be a new, effective chemical market ready in the near future.
What small ruminant livestock owners are left with, if they want to be pasture based, is learning how to co-exist with the Haemonchus contortus parasite.
Large part of management
Pasture management is a large part of parasite management. Unfortunately, on farm research here in Ohio has proven that the L3 larvae are able to survive on pastures for at least 90 days and quite probably longer, during the growing season. There is also evidence that larvae can survive Ohio winters and be waiting to infect grazing animals the next spring.
So, standard rotational grazing system management will not be effective in allowing the grazier to avoid or decrease parasite burdens.
At this point you may be on the verge of throwing your hands up in the air in surrender, but the good news is that research and on-farm studies in Ohio and other states have helped to identify some management strategies for small ruminant animals.
For instance, on-farm studies in Ohio have consistently shown that about 20 percent of the animals in a flock or herd are responsible for 60 to 80 percent of the eggs being shed.
Identifying and then selectively treating only these animals with an effective de-wormer can result in better animal health, less pasture contamination and will minimize the development of parasite resistance to the de-wormer.
On-farm studies have shown that removing the stress of lactation from ewes and does allows their immune system to recover, the number of eggs being shed drops to very low levels and they are able to handle re-grazing pastures where parasite eggs were shed in a previous grazing pass.
Therefore, early weaning where lambs and kids move to safe pastures and ewes and does re-visit previously grazed pastures might become a management strategy.
In August, results of on-farm sheep and parasite control options research in Ohio over the past several years will be presented in a series of three web-ex meetings and one Saturday field day.
Save the dates
Pasture management will be a key component of the discussions. The web ex technology will allow the viewing of these meetings throughout the state, with opportunities to ask questions of the presenters from any viewing location. Extension offices throughout the state will be able to log in and host the meetings.
At this point save the evenings of Aug. 4, 18 and 25 from 7 p.m. to 9 p.m. for the web ex meetings and Aug. 27 for the field day in the Wooster area. Specific details will be available by late June.
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