Small ruminant parasite control (Proceedings)

The most common reason for anemia in the small ruminant is internal parasitism. Hemonchus contortus (the barber pole worm) is a voracious bloodsucker that typically resides in the abomasum. The condition may occur in both young stock and adults alike. With the ever increasing issue of parasite resistance, practitioners will be faced with the severely anemic small ruminant. Providing that there are no other serious disease conditions, these cases can have successful outcomes.

The clinically parasitized individual

The case presentation is quite typical. The animal is weak and often down. Mucous membranes are pale pink to white. The mucous membranes of the eye provide the most consistent coloring although mucous membranes of the oral cavity and vagina may also be examined. The heart and respiratory rates are usually elevated. Diarrhea may or may not be present. Often times, there is a history of deworming, even recent deworming.

If the client is bringing the animal into your clinic and it is coming as a probable anemia, the client should bring a healthy blood donor. Have the client make sure that the donor's mucous membranes are bright pink to red. It is important to not stress or excite the patient in that this could lead to collapse and possibly death due to anoxia. Most cases, that we have dealt with in Tennessee, are too weak to get excessively stressed. A pack cell volume (PCV), total protein (TP), and fecal floatation help to confirm the diagnosis of anemia due to internal parasitism. A blood transfusion is the treatment of choice if the PCV is 10 or less. The lowest PCV seen by the author at least a couple of times was 4. These cases were transfused successfully and sent home. Animals' PCVs as low as 9 or 10 can recover without blood transfusions if treated with effective anthelmintics but blood transfusions help ensure recovery and recovery will be faster. An animal with a PCV of 11-15 may benefit from a transfusion but this is not always necessary for a successful outcome. The TP is usually low as well and fecal floatation should demonstrate numerous parasite eggs. About 50% of the time, the case is complicated by coccidia.

Steps in performing a blood transfusion

     1. Place a temporary jugular catheter in the anemic animal.

     2. Make sure the blood donor is healthy by checking mucous membrane color and running a PCV. The PCV should preferably be above 30 but we have used donors with PCVs between 20 and 30 without incident.

     3. Place a jugular catheter in the donor animal (a needle may be used as well as long as there is good restraint).

     4. Collect blood from the donor; 10-20 ml/kg can be collected from a healthy donor. We typically collect 10-15 ml/kg which equates to 500 to 750 ml from a 50 kg goat. Blood can be collected in sterile IV bags that have had sodium citrate added as an anticoagulant. One hundred ml of a 4% Na citrate solution should be added to a 1 liter bag (extrapolate with smaller bags). The bag should be agitated during collection to prevent clotting.

     5. Transfuse donor blood into patient. Infuse at a slow drip for the first 15 minutes, if no reactions occur, the rest of the volume may be transfused at a rapid drip. Reactions are quite rare in small ruminants during the first transfusion. Reactions will likely become more frequent if subsequent (days to weeks later) transfusions are necessary. Epinephrine is the drug of choice if a reaction occurs. If a serious reaction does occur, blood may be transfused very slowly or another donor should

Post-transfusion, the patient will often be noticeably stronger and will eat. We typically keep the animals overnight and monitor the PCV and TP the next day. You can expect a 5-10 point rise in the PCV....should at least be in the teens. Iron injections are often not necessary but should be considered for animals that repeatedly become anemic over a short time period.

It is also acknowledged that certain parts of the United States have a greater problem with internal parasites other than H. contortus. These cases usually present with ill thrift, diarrhea, bottle jaw, and low serum protein. Blood transfusion is not usually necessary and deworming with an effective anthelmintic is the treatment of choice. However blood transfusions will help to elevate the protein levels and might be considered in special cases. Some of the authors own sheep (dewormed prior to lambing only with ivermectin) developed muzzle edema and bottle jaw. Three older ewes, 2 yearling ewe lambs, and 4 young lambs were placed on a ½ acre lot to allow the primary pasture to grow and be cut for hay. The sheep were on the small pasture for 1.5 months and had eaten the pasture down to about an inch in height. Only the older ewes developed signs of parasitism. The ewes were not anemic but had low total proteins and extreme muzzle edema and bottle jaw. The older ewe were dewormed with moxidectin and signs of edema were gone within 2 days.

Herd Management and the Internal Parasite Control Program

When animals become anemic or hypoproteinemic due to internal parasitism, the veterinarian should examine the client's parasite control program. The means of controlling internal parasites has changed drastically over the last 10 years and the "best" method of control will vary depending on the region of the country. Even though the idea that internal parasite resistance was developing to anthelmintics, routine deworming, more frequent deworming, using higher dosages and multiple products at the same time was commonly done. All of these methods just increased internal parasite resistance. The following internal parasite control primarily pertains to flocks and herds in which Hemonchus contortus is the main problem.

Control Strategies

     #1 Deworm only when necessary on an individual animal basis. Don't deworm animals with bright pink to red mucous membranes. One can use FAMACHA to determine which animals need to be dewormed. If the mucous membranes are pale pink to white, deworming is necessary. Animals with mucous membranes somewhere between red and white may or may not be dewormed based on client/veterinarian decisions on which way to err. These animals should be reevaluated in a couple of weeks.

     #2 Document that the dewormer is effective. Fecal egg counts should be conducted on a portion of the herd. Collect and run fecal egg counts, deworm, wait 10-14 days and run fecals again. Fecal egg counts should be reduced by > 90% if resistance is minimal. If fecal egg counts are not reduced to an acceptable level, repeat the procedure with the next anthelmintic. An anthelmintic can still be beneficial as long as the egg count reduction is greater than 50%.

     #3 Don't overstock. An anemic llama was presented for a blood transfusion. It had come from a farm that had 30 llamas on 2.5 acres. The owners indicated that they had no short term solution to the stocking rate. Internal parasite problems will continue to be problems in these situations. Worm larvae do not migrate more than 12 inches from a manure pile but when stocking density is high there will be fewer grazing areas that aren't within 12 inches of manure.

     #4 Provide access to browse. Worm larvae only migrate up to 3 inches on plants. Allowing longer length pasture and brush access will decrease the number of parasites ingested.

     #5 Graze horses or cattle with small ruminants. Sheep, goats, and camelids all share internal parasites, however horses or cattle will consume small ruminant parasites and vice versa with little detrimental effect. When cattle or horses cannot be grazed with small ruminants, try rotational grazing such as cattle on pasture for 1 month then sheep on pasture for 1 month.

     #6 Save moxidectin for special cases. Moxidectin is considered the last line dewormer and should be reserved for cases in which all other dewormers have failed or cases that may die if an effective dewormer is not used. This dewormer should not ever be the routine dewormer.

     #7 Administer avermectins orally only. One of the reasons that resistance developed to avermectins is that the product could be administered subcutaneously. This used to be considered a good thing in the product could last up to 21 days. The problem with this is that the level of product available decreased over those 21 days which exposed potentially susceptible parasites to ineffective levels and leading to resistance.

     #8 Routinely deworm 2 weeks prior to parturition. Because the stress of parturition results in increased shedding of internal parasite eggs, this is one of the few times that routine deworming can be recommended. One other instance in which routine deworming might be advised for neonates is at the time of weaning. Deworm with oral products only.

     #9 Realize that some small ruminants simply cannot tolerate worms (need to be culled). It has been said that 80% of the pasture parasite load comes from 20% of the animals on the pasture. Conversely, there are some animals that may never need to be dewormed. These are the keepers; the ones that you want offspring from.

     #10 Some eggs are expected and the # of eggs does not necessarily indicate the need to deworm. If a small ruminant is demonstrating signs of parasitism, deworming is important. However, most small ruminants will have some eggs...sometimes many eggs but if signs of parasitism are absent, deworming is not recommended.

     #11 Use the proper dose and route of administration. It is better to overdose than underdose as underdosing is more likely to lead to resistance. When possible, weigh each animal prior to deworming. Most of the dewormers are approved for sheep and the dosages suggested should be followed. Few dewormers are approved for goats so as a general rule, the sheep or cattle dosage should be doubled for goats for all products except for levamisole which should be dosed at 1.5 times the sheep dose. The reason for the increased dosage in goats is due to a proportionately larger liver (more rapid metabolism) and more rapid gut transit time. Oral administration is highly preferred and it is important to deposit avermectin products over the base of the tongue which allows the product to enter the rumen rather than the abomasum. This allows longer contact time in the gut. In addition, withholding feed for 12 hours prior to dewormer administration and for 12 hours after leads to slower gut transit time and longer dewormer contact with internal parasites.

Successful management of the severely parasitized small ruminant can be performed both easily and economically. However, the parasitized individual is just the tip of the iceberg. Controlling internal parasites in small ruminant herds or flocks requires a judicious deworming strategy, an effective dewomer, and pasture management.