Close this window to return to IVIS www.ivis.org Proceeding of the NAVC North American Veterinary Conference Jan. 13-27, 2007, Orlando, Florida www.tnavc.org Reprinted in the IVIS website with the permission of the NAVC http://www.ivis.org/
The North American Veterinary Conference 2007 SMALL RUMINANT TIPS FOR SMALL ANIMAL PRACTITIONERS Joseph Hoyt Snyder, DVM Myrtle Veterinary Hospital Myrtle Point, OR A SMALL RUMINANT IS A RUMINANT! For those used to working with small animals and equines, it is important to remember sheep, goats, llamas, alpacas, and deer have some fundamental differences in their anatomy and physiology by virtue of the fact that they are ruminants. From the abomasum on, they function much like other mammalian species; but prior to the abomasum is that formidable forestomach complex. The rumen system allows ruminants to eat what other mammals can't: plant fiber and cellulose. Microflora in the rumen break down these materials and the ruminant is nourished by the leftovers of microfloral digestion or by digesting the micro organisms after they die. This has allowed small ruminants to survive in climates and on diets that other animals would find totally inhospitable. Goats and camelids, in particular, are amazingly able to live on material that would not sustain other species, as well as preserve nitrogen and water extremely well. When such animals are fed highly concentrated diets, in both energy and protein, it may actually be detrimental to their health, rather than beneficial as is often perceived by the owner. When devising a feeding program for a small ruminant, it is essential to realize that we are actually feeding a colony of micro-organisms which, in turn, are feeding the ruminant. The rumen contains numerous species of microorganisms, few of which have been identified and even fewer characterized. They can do amazing things from metabolizing pyrolizidine alkaloids to breaking down petroleum. But for all its diversity, the rumen is a critically balanced environment. Anyone who has brewed beer or made wine knows how finicky those cultures can be, and the rumen is not unlike that, only far more complex. Its complexity gives it some buffering capacity, but when it fails it can fail abruptly and catastrophically. Sudden changes in diet are often disastrous for small ruminants, especially when they involve increasing the amount of concentrate in the diet, or changing the nature or a concentrate that forms a major portion of the diet. Dietary changes should always be made slowly. A good questioning about diet and changes therein is a critical part of history taking for a sick small ruminant. Small ruminants are perfectly capable of living on hay and forage alone for routine maintenance; and will be healthier on that diet than one rich in concentrates. Many, many of the diseases that plague these animals are due all or in part to diet for which these animals are not acclimated. Any medication given orally to a ruminant has to pass through the rumen. It is necessary to consider both the effect of the medication on the rumen and the effect of the rumen on the medication. Very few antibiotics, for 664 example, can make it through the rumen intact and have any systemic effect on an infectious disease. A common mistake is to give oral trimethoprim sulfa combinations to small ruminants, a practice often justified because the product is used in horses, which are monogastrics. In fact, trimethoprim is completely inactivated in the rumen and cannot be found in the blood stream after oral administration. Although sulfonamides in general escape rumen degradation, there is so little sulfa in the combination products that it is of no therapeutic use. Tetracycline and sulfonamides can be given orally to small ruminants, but not much else in the way of antibiotics. In counterpoint, some compounds given orally can have negative effects on rumen flora, causing further problems in an already compromised animal. Small ruminants are born without a developed forestomach system, and can be treated as monogastrics up to approximately 3 weeks of age. Evaluation of rumen function should be part of every small ruminant physical exam. This is a simple as listening to the left paralumbar fossa with a stethoscope. Strong primary rumen contractions should be heard, and felt, every two or three minutes, with two or three secondary contractions between. Slow, weak, or absent rumen contractions suggest weakness, dietary problems, or severe metabolic disease. Gassy or bubbly borborygmi such as one hears in a horse are not normal sounds for a rumen and should be cause for concern. In addition, the rumen can be balloted with a fist. Normal rumen has a solid, doughy consistency. Splashy contents are bad, and may suggest grain overload. ANALGESIA AND PAIN MANAGEMENT Because small ruminants are relatively small, easily intimidated prey species, it is not difficult to restrain them physically for painful or stressful procedures. Historically, this has led to a cavalier approach to analgesia and pain management when working with them. We need to remember that they are just as susceptible to pain and suffering as those species with which we more closely identify, and treat them accordingly. There has been much concern expressed about the potential for toxicity from use of lidocaine in small ruminants, especially goats. Please do not deny your patients adequate anesthesia because of this concern. The recommended limit, 6 mg/kg of lidocaine is very conservative. It has been calculated as high as 13 mg/kg. Six mg/kg comes to 12 ml of 2% lidocaine in a 40 kg (88 lb) goat. That is easily enough to block for a dehorning, castration, or cesarean section. Lidocaine may also be diluted to 1% or ½% to allow for infusion of larger volumes, especially in very small animals. Dilution will not reduce efficacy of the block, but may shorten the duration of anesthesia. Because general anesthetic agents such as isoflurane and ketamine provide little or no analgesia, it is advisable to use local anesthetic agents even when general anesthesia has been induced. Common techniques with local anesthesia include cornual blocks for dehorning, epidural anesthesia, paralumbar blocks for abdominal surgery, and distal limb (Bier) blocks. It also should be used for
Small Animal Miscellaneous suturing lacerations, lancing abscesses, or removing lumps and tumors, including testicles. Bupivacaine may also be used. It provides anesthesia of much longer duration, but also takes much longer to take effect, which limits its usefulness. A conservative maximum dose for bupivacaine is 2 mg/kg. Lidocaine as manufactured has a very low ph, which makes it painful on injection. Adding a small amount of sodium bicarbonate to the lidocaine just before injection will create a more neutral ph and much less painful injection. This effect is most noticeable in goats, with their tendency to vocalize readily and loudly when subjected to painful procedures. It should not be ignored in other species which are less vocal about noxious stimuli. Suggestions range from 1:5 to 1:9 for dilution. Our experience suggests that one part 8.4% bicarbonate to 9 parts lidocaine is adequate. The solution will become cloudy, but it seems to function just fine in the tissues. The alpha-2 agonist sedative analgesics are excellent tools for procedures that require restraint and protection from pain. They are best used in cocktails with an opiod. Xylazine is the most used drug and has the most history. It is important to remember that sheep and goats are very sensitive to the effects of alpha-2 agonists. Doses are very small and animals should be monitored closely. Recommended concurrent use of an opiod will reduce the dose by about half, making measurement even more critical, but also reducing potential for adverse consequences. Intravenous injection results in rapid sedation and quicker recovery. Intramuscular injection requires more drug and has a slower onset, but my practitioners find the sedation smoother with IM induction. Availability of effective reversing agents has made use of these drugs much safer. A reversing agent should be on hand whenever an alpha-2 agonist is used. These include atipamezole, tolazoline, and yohimbine. Reversing the sedative properties of an alpha-2 agonist also reverses the analgesic properties. Opiods, either alone or in combination with alpha-2 agonists are a potent tool for pain management. The most commonly used agent is the agonist/antagonist butorphanol, available as a 10 mg/ml injectable. It has minor sedative effect and considerable analgesic effect. Analgesia is rather short lived, especially by IV injection, but can be prolonged by using intramuscularly or subcutaneously. Ten mg of butorphanol IM is often used by itself in llamas or alpacas for sedation for minor procedures. While not producing many outward signs of sedation, it makes them stand much more quietly and tolerantly for shearing, dental work, foot work, etc. Buprenorphine and morphine may also be used if more profound pain relief is required. Fentanyl patches have been used in small ruminants, but we have little data to suggest how well the drug is absorbed and how reliably. Furthermore establishing drug withdrawal would be problematical. Nonsteroidal antiinflammatory drugs (NSAIDs) are not available with small ruminant labels either, but have a place in management of pain. Aspirin has been used by sheep and goat producers for decades with greater or lesser degree of success. Flunixin may be given intravenously at doses extrapolated from the bovine. Intramuscular administration of flunixin should be avoided as the solution is very irritating and may cause serious injection site reactions. There have also been issues with violative flunixin residues after IM injection. Nevertheless, flunixin is the only NSAID available in the US with a food animal label of any kind. Phenylbutazone has been used in small ruminants. At this time, phenylbutazone is prohibited from use in lactating dairy cows and wisdom would suggest we extend that ban to milking goats and sheep as well. If used in other situations, a very long withdrawal should be established. Other NSAIDs have been used in small ruminants empirically, but good data are not available. Meloxicam is available in other countries as an injectable product for cattle at a dose of 0.5 mg/kg single dose IV or subcutaneous injection with withdrawal of 15 days for meat and 5 days for milk. Since most NSAIDs seem to be reasonably well absorbed by oral administration in ruminants, it would be reasonable to believe that oral use of meloxicam would also be affective. This would provide a manageable option for maintaining some ongoing level of pain management Consultation with FARAD would be helpful in establishing adequate withdrawal. SURGERY AND ANESTHETIC CONSIDERATIONS Euthanasia Euthanasia of small ruminants can be problematic. There are few, if any, places that will receive sheep or goats that have died for any reason. Cremation is acceptable for disposal but may be unavailable or prohibitively expensive. Deep burial is also acceptable. Pentobarbital euthanasia solutions may be used, but such animals must be protected from consumption by carrion eaters because of toxicity issues. While usual mammalian doses of pentobarbital are effective in most cases, some animals, notably sheep approaching circulatory failure, may require much larger doses than expected. Euthanasia by well placed gun shot from a trained operator is considered acceptably humane, with the emphasis on well placed and trained. Animals so euthanatized do not present a risk to those consuming their flesh. Work is being done on developing euthanasia cocktails for humane euthanasia without leaving toxic residues. One such would involve sedation with xylazine followed by anesthesia with thiopental followed by intravenous concentrated potassium chloride until cardiac arrest. Others have suggested use of ketamine to induce anesthesia, although some have questions about complete loss of consciousness under ketamine. Using such a protocol, humane considerations require that a deep level of anesthesia be induced before administration of potassium chloride. 665
The North American Veterinary Conference 2007 Table 1. Drug Regimens for Sedation and General Anesthesia in Small Ruminants LLAMAS (mg/kg) ALPACAS (mg/kg) SEDATION Butorphanol 10 mg IM 10 mg IM Xylazine 0.2 0.3 IV 0.4 0.6 IM 0.3 0.4 IV 0.6 0.8 IM Butorphanol/Xylazine to X (0.4) + B 0.1 IV recumbency IV/IM Ketamine Stun Xylazine, ketamine butorphanol X (0.2 0.3) + K (0.2 0.3) + B (0.07 0.1) IV X (0.2-0.5) + K (0.2 0.5) IV BKX Ketamine 1g + 100 mg xylazine + 10 mg butorphanol + B (0.05 0.1) IM 1.0 2.0 ml of mixture IV 0.5 1.5 mlof mixture IV Reversal: Tolazoline 1.1 mg/kg (0.5 mg/lb) slow IV GENERAL ANESTHESIA IM BKX X 0.3 + K 3.7 + B 0.037 (or) 1 ml/50 lb + 1 ml Xylazine & ketamine IV X 0.2 0.55 IV (or) 1.1 IM when sedation is profound give K 2.2 IV Telazol 4.7 6.0 IM GOATS (mg/kg) X 0.4 + K 4.6 + B 0.04 (or) 1 ml/40 lb + 1 ml SHEEP (mg/kg) SEDATION Xylazine & butorphanol Medetomidine X 0.1 0.2 IV B 0.01 0.02 IV deep sedation for 60 min 0.001 0.007 IV 0.01 0.04 IM Reversal: Tolazoline 2.2 mg/kg (1 mg/lb) slow IV Same as goats X 0.1 0.2 IV B 0.01 0.02 IV deep sedation for 60 min 0.001 0.007 IV 0.01 0.04 IM GENERAL ANESTHESIA Ketamine & Detomidine Xylazine & Ketamine Telazol K 0.1 ml/10 lb + D 0.01 ml/10 lb IV add butorphanol 0.4 IV for added analgesia. Reversal: ½ dose of D as Atipamezole IM X 0.22 IM wait 10 min then K 11 IM (have also given1/2 dose IV T 2 5 IV + butorphanol 0.1 IV for additional time X 0.22 IM wait 10 min then K 10 15 IM T 2 4 IV + butorphanol 0.1 IV for additional time PREVENTIVE MEDICINE Vaccination programs for production small ruminants can be a bit complex. For the pet or small flock population that small animal practitioners see, very little is necessary. In most parts of the country, an annual combination clostridial vaccine including tetanus is advised. The most used in small ruminants is Covexin 8 now marketed by Schering-Plough. In areas where blackleg and liver disease are not seen, especially in 666 goats, an annual vaccination with C. perfringens types C and D plus tetanus is adequate. Boehringer Ingelheim's BarVac CDT is the product of choice. A word of warning about clostridial vaccines: They are rather reactive by nature and frequently cause lumps or sterile abscesses at injection sites when given subcutaneously. These cannot be entirely avoided although sterile technique and massaging of injection sites will help. Clients should be forewarned of this eventuality. Some clients prefer
Small Animal Miscellaneous intramuscular injection of these products, but it should be discouraged. Reactions will still occur. They are just out of sight in the muscle; but more of a problem there than under the skin. Other vaccines are used for contagious abscesses, soremouth, abortion diseases, footrot, and respiratory disease. These products should be used with caution and only when a need is established based on diagnosis and history in the flock. Sheep and goats are susceptible to contagious foot rot, which is subject of an entire presentation in itself. Most pet and small flock animals do not get sufficient exercise on hard surfaces to maintain good hoof health, so a regular foot trimming program should be established. If foot rot is not a problem in a small flock, then strict quarantine should be required for all new additions, as foot rot is a devastating introduction. If footrot is present in a flock, it can be eliminated through aggressive trimming, soaking, and culling of chronically infected animals. If elimination is not possible due to management limitations, regular trimming and foot soaking in zinc sulfate with help control the problem Footrot vaccine is available, but is not considered curative on a flock level. It is even more reactive than clostridial vaccine and should be used with care. Llama and alpaca feet also require regular trimming in most environments. How frequently trimming is required in any species is dependent on climate, activity level, and substrate. Parasite control is critical in all small ruminant species, as they tend to be more sensitive to severe internal parasite infestation than cattle. Resistance to available anthelmintics in commercial flocks is becoming a severe problem and can be brought to small flocks through purchases or developed on site by poor deworming practices. Although a less than perfect tool, fecal flotation is out best means to evaluate parasite levels and recommend treatment programs. Fecal exams should be quantitative, either centrifuged sugar flotations or modified McMaster technique. Under warm, humid conditions, a generation of parasites can cycle through a small ruminant in as little as three weeks, so contamination can reach serious levels really rapidly. In order effectively to control parasites while maintaining efficacy of our products, the following rules apply. Parasites should be monitored and aggressively treated during periods of peak transmission, ie, warm humid seasons. A good rule of thumb is: if the grass is growing rapidly, the parasites are multiplying rapidly. During periods of dry, very hot, or very cold weather, parasites are not well transmitted and less control is necessary. It is advisable to treat animals prior to the onset of adverse weather. In much of North America treatment in the late fall, after cold weather has arrived, will keep animals relatively parasite free through the winter. In parts of the South, it may be more advisable to deworm at the beginning of the very hot or dry summer season. Avoid use of injectable or pour-on dewormers in small ruminants, concentrating instead on orally administered products. Injectables have been shown to increase the rate at which parasites develop resistance to a product. APPROPRIATE USE OF MEDICATIONS Because almost all drugs used in small ruminants are used in an extra label manner; and because small ruminants are considered to be food animals; veterinarians who work with them should be very familiar with and follow AMDUCA regulations concerning food animals. There are a few drugs that are banned from extra label use in food animals under any circumstances. Those of interest to us include the fluoroquinolones, including enrofloxacin; nitrofurans; chloramphenicol; and nitroimidazoles, including metronidazole. In addition, phenylbutazone and sulfonamides other than sulfadimethoxine are banned from use in lactating dairy cattle, which suggests that use in goats or sheep used for milk production should also be avoided. Although not specifically prohibited by law, the AVMA, AABP, and AASRP have all passed resolutions against the use of gentamycin in food animals because of the difficulty in establishing any withdrawal time. Establishment of reasonable withdrawal time should always be considered before a drug is given to a food animal. 667