Deworming Your Flock
Some herdsmen have a regular deworming program for their sheep even though Blackbelly's have a certain amount of parasitic resistance.
I'd like to first remark that EVERY flock has parasites. The most common parasite is the coccidia (cock-sid-ee-uh) protozoa and although an outbreak is something a new shepherd should be on the look for, there are some common things you should be doing in order to keep your flock healthy and reduce the chance of ever having an outbreak. This picture shows the Coccidia oocysts (egg sack of sorts) found in the feces of infected sheep (NADIS Photo) .
It's particularly nice to have this breed of sheep because this problem is rather forgiving for new shepherds. What I speak of is the fact that Barbados Blackbelly and American Blackbelly are fairly resistant to parasite infestation - it's in the genes.
Many books and veterinarians will INSIST on some sort of regular de-worming program for your flock. But after you ask the obvious question, "Why?" and get the obvious answer "Because you have worms and they can hurt your sheep," the very next question you should ask and insist on proof is "How do you know they're hurting my sheep?"
Blackbelly do in fact have worms like many other sheep. But a certain amount of worms is acceptable so long the parasites don't take so much blood that they make your sheep anemic (meaning that they are short on blood and become weak). The real surprise is that the number of worms a Blackbelly can handle is far more than the standard sheep.
How Do You Know if You're Sheep is Anemic? (FAMACHA)
This is something I'll give a brief detail on, but look at the links provided and learn more about it by reading and researching it. The technique is called "FAMACHA" and was developed in S. Africa. The essence of the technique is that as parasitic worms infest the sheep or goat host they begin to draw blood from the animal as food. As the numbers of these blood suckers increases the amount of usable blood for the host decreases.
Make sense so far? Good.
When an animal (like you) has plenty of blood, it flows freely to all parts of the body. But when there isn't enough blood, your body puts it where it needs it most or else your blood pressure drops when the anemia becomes severe. In a way, it's like your hands getting cold and circulation cut off to your fingers and toes when the trunk of your body starts to go into hypothermia from the cold. The body is placing blood where it needs it most to stay warm - the vital organs needed to sustain life.
In sheep and goat the tissue around the eyes (under the eyelids) becomes white when the animal is becoming anemic. There is a color "spectrum", from pink to white, that correlates very well with the number of parasites infecting the host and the animals ability to tolerate the worm burden.
Please read more about it;
ATTRA - Managing Internal Parasites in Sheep and Goats (look at page 5)
SCSRPC - Southern Consortium for Small Ruminant Parasite Control
International Kiko Goat Association - FAMACHA EVALUATION
Before you decide that a pesticide for parasitic worms (a parasiticide) is needed, investigate this method and try everything BEFORE using these chemicals. It may be that you're wasting your money and creating resistant worms that you won't be able to kill when you need to.
What do parasites do to a sheep and how do they spread?
In very basic terms, the protozoa or worms eat the inside lining of the sheep intestine to steel nutrients (blood usually). As a result, the sheep can be damaged internally and bleed, absorb nutrients less efficiently as it ages and the organs are damaged, or have diarrhea (scours) all of which may lead to poor nutrition, slow growth, damage to vital organs, and allows for other organisms to take advantage of the weakened animal. If left unchecked, the sheep may be unable to defend against a significant viral or bacterial infection. Some of these parasites can infest the heart, liver, stomach, intestines, and bloodstream.
The things you should be looking for are:
a) Diarrhea that contains mucus or blood
b) No weight gain or even weight loss with normal eating
c) Dehydration
d) Fever
e) Anemia (due to blood loss)
f) Loss of appetite
g) Low energy, lethargic
And though many of these symptoms are common to many health issues in sheep, the good shepherd will take preventative measures, such as good nutrition, sanitation, and preventative medication to reduce the possibility of serious "flock" infestation.
Coccidia are the most common protozoa found in sheep and are spread through sheep orally. The oocyst of a protozoa is discarded in the feces of an infected sheep and deposited on grass, feeding areas, or in the drinking water shared by other sheep where it is taken up into an uninfected host/sheep when grazing or laying on infected ground (and for lambs where transmission is through feces contamination on the ewe's utters). The oocyst germinates in the stomach where the protozoa multiply and the life cycle begins again with the production of more oocysts being deposited in the feces and discharged.
In adult sheep a certain amount of immunity exists because of prior exposure, however in younger lambs where immunity is not yet present the protozoa can quickly multiply and overwhelm a small and growing lamb. This is especially true under conditions of extreme stress such as changing feed conditions (being weaned for example) or rapid changes in the type of environment (being moved to a new pasture or pen, new people, being transported). It's highly suggested that a medicated food containing decoquinate be administered to pregnant ewes starting 1 week before expected lambing and continued for at least 28 days. While this will not cure a coccidia infection it will prevent its spread to the newborn lamb until it has had time gain weight and an immune response.
With worms, the spread is primarily through the foraged pasture where the larva grow and cling to vegetation, and later are consumed by the host that is foraging on that vegetation. High sheep density (a crowded pasture) and not allowing for sufficient time for land to rest maintains and encourages the parasite's life cycle.
Risk Reduction -
As the old wives tales go, "An ounce of prevention is worth a pound of cure" -- a wise person will heed this even though Barbados Blackbelly and American Blackbelly seem to have better than average control over parasites.
First consider what type of herdsman you are. If you're the type that free-ranges their sheep into the pasture, then you're style of flock management is call "Extensive" and some refer to it as "Range" if your sheep only see that pasture once a year and moves on to other pastures. On the other hand, if you keep your sheep indoors, or in closed pens, and reduce their access to forage then your style of flock management is called "Intensive."
Intensive Management -
Intensive management will give the shepherd close control over circulation of the protozoa among other animals if multiple pens are used where contact with other flocks is reduced. However, an outbreak in one pen can quickly become a problem if left unchecked and improper care is given. The opposite is true for most worms in this situation being that they need a pasture to mature from the larval state to a mature organism. This is something to consider since wet grasses help spread parasitic worms and by keeping your sheep penned up until the grass is dry that can reduce some of the exposure.
The best prevention for coccidia outbreaks is frequently changing bedding and litter, decontamination of the pens, keeping the pens dry, decreased sheep density within the confined pen, regular high protein diets (because healthy sheep are better able to fight an attack), periodic fecal testing to ensure low numbers of the protozoa are present (perhaps quarterly checks) and a proper response, and implementing regular preventative medication of the flock/s.
Extensive Management -
Free ranging sheep, or sheep that are partially supplemented with feed and share common sources of water and feed bunks/bins/troughs are likely to spread coccidia oocysts in unkept areas such as shelters used in bad weather, poorly designed mineral feeders, or by feces being swept into drinking water or feed areas.
Unfortunately there are not a lot of people want to take the time to look into parasite problems so it's easy to overlook issues if you don't investigate. I've read in at least one book where the author suggested that common areas only be cleaned at 6-month intervals so that less work was performed and greater amounts of manure could be collected (for sale). The area was also associated with a nearby common food source for the flock. Because of the increased contact with the feed and the greater density of sheep this was really poor advice because it became an area where it was an excellent opportunity for quickly spreading all kinds of parasites to the rest of their flock, especially coccidia.
Another advantage offered by extensive flock management is the possibility of pasture rotation. Pasture rotation requires letting a large segment of your land rest for a period of time so that sunlight and dryness can kill a large number of the organism before returning your flock to that pasture.
It's been found that if land does not rest for more than 60 - 70 days there may be an even greater chance for spread of some parasites because herdsmen tend to graze these pastures with higher populations; higher density of sheep acts to increase the problem and spread. Since 80% of the parasites reside in the first 2 inches of forage, a short rotation doesn't allow plants to mature in the pasture and combined with a high density of animals the combination can work against your fight.
And just like intensive flock management, a regular program of preventative medication is suggested even if you are clean and you have pasture rotation.
Worms in General -
Since there are so many varieties of possible parasitic worms, protozoa, and their associated life cycles that it's impossible to cover all of these without having a degree in Parasitology (Yes, this is a real discipline). Making this short and sweet, if you feel that you're not able to rotate your flock through the pasture so as to naturally rest it and reduce the number of parasites in your grazing land, then you'll probably need exercise some form of medication as much as quarterly to keep a potential problem under control. Consult your local large animal veterinarian in your area since this problem varies significantly in different parts of the country.
What kind of medication? How often do I treat my flock?
As you start to investigate this topic more realize that the various groups providing expert information are experts in their own "Climate". There are big differences in the kinds of parasites between vastly different types of humidity, heat, vegetation, other animals (like deer), and multi-species pasture lands. If you're new to this (like all beginners are) then the first thing you'll need to do is fecal testing to determine the types of parasites in your sheep. This is something you should consult your local veterinarian about BEFORE starting a deworming program. It may be that you need to deworm quarterly (or even every two weeks) or that you may not need to do it all since we have a special breed.
Deworming Products (just to give you a variety to look at and ask about).
Each have their own specification for dosage and application and since I'm not a veterinarian (and neither are you) I recommend consulting the experts 
before purchasing one of these willy nilly.
According to many sources the best time to de-worm is 2-4 weeks prior to lambing. This gives the lamb the best chance to nurse without being infected by the mother. Know the medications affect on pregnant ewes and the duration of time it takes to leave the sheep before slaughter (This is often called "Withdrawal").
20 cc Drench Syringe Used for Medicines and Dewormers
Coccidia:
Decoquinate, Deccox - This drug is always mixed with feed is mainly for "Prevention" and not cure of Coccidiosis in ruminants. It's generally used as when animals are being taken to show or administered to ewes just prior to lambing to help prevent contamination during feeding.
Corid, amprolium - This product treats for coccidiosis. Available in drench or powder this must be used for 5 days and can be added to drinking water for control and treatment.
Worms:Consult your large animal veterinarian for your area. Some have suggested that a rotation of these parasiticides be used every time you use one to help prevent parasite tolerance/resistance. These are the most popular names being used today.
Ivermectin, Ivomec Sheep Drench - Works to kill or quickly expel nematode parasites, this also works as a type of insecticide and kills mites. This is available in a paste or drench.
Fenbendazole, Safe-guard, Panacur - These products is not approved for use in sheep, although many producers use it in young animals to control lungworms, stomach worms and intestinal worms. The product will also control tapeworms when the dosage is doubled.
Valbazen - Effective in the removal and control of liver flukes, tape worms, stomach worms, intestinal worms and lungworms. Available as a drench.
Levamisol, Levasole, or Prohibit - Effective against nematode worms that infect the abomasum of ruminants (Haemonchus, Ostertagia, Trichostrongylus colubriformis). This includes the barber pole worm. This is available in a drench (Syringe tube into the throat/stomach) as well as in large pills (Bolus).
Cydectin - Used for control of external parasites and lungworm. This is an injectable solution made subcutaneously (under the skin) at a dose of 3.4 - 5.7 mL per 100 lbs body weight (4 mL is commonly used with good results).