Postsurgical Pain Relief
It is difficult to assess pain in goats, especially if the animals are not habituated to contact with people. Goats are famous for screaming when subjected to nothing more than manual restraint, and yet do not always vocalize or show restless behavior or struggling after surgery that might be expected to cause pain.
Inappetence and depression are possible indicators of pain (Hendrickson et al. 1996), as are trembling and bruxism. Analgesics are most effective if administered before pain actually develops (preemptive analgesia).Morphine has been used as an epidural for pain relief after abdominal or limb surgery (Pablo 1993; Clarke et al. 2014). Morphine binds to opiate receptors in the central and peripheral nervous system and inhibits the release of pain-related neurotransmitters. Preservative-free morphine is diluted in saline and administered at 0.1 mg/kg in the lumbosacral space, using aseptic technique and a spinal needle. Duration of action is variable, but may be as long as 24 hours. Epidural bupivacaine at 1.5 mg/kg affords some pain relief but causes prolonged recumbency (Hendrickson et al. 1996). Lower doses of bupivacaine are mixed with morphine to provide surgical analgesia and postoperative pain relief.
IM opioids are not great for analgesia but have also been used, including butorphanol at 0.05-0.2 mg/kg every six hours and pethidine at 2-4 mg/kg (Hall et al. 2001; Riebold 2015) and morphine at 0.2-0.5 mg/kg (Clarke et al. 2014). Buprenorphine (at 0.02 mg/kg IM or IV) does not appear to be suitable for postsurgical pain relief, because it causes agitation and inhibits rumination (Ingvast-Larsson et al. 2007).
Fentanyl is a synthetic opioid agonist that has a short duration of action when given IV (Kyles 1998; Carroll et al. 1999). Transdermal fentanyl can be administered via a commercially available patch to provide more prolonged blood concentrations.
Hair is clipped on the side of the neck and a 50 pg/hr patch is applied to the skin of an adult goat, under a protective bandage. The patch should be placed 12 (Burke et al. 2017) to 24 hours before surgery for best effect. Because goats show variable and inconsistent absorption of fentanyl from the patch (Carroll et al. 1999), they need to be monitored closely in case additional analgesia is required. Caution should be taken when the goat is on heat support, as heat applied to the patch can significantly increase absorption rate.A variety of non-steroidal anti-inflammatory drugs have been administered to goats, often extrapolating from pharmacokinetic and pharmacodynamic data collected for other species (Lees et al. 2004) and with the assumption that pain relief is also supplied. Salicylates are poorly absorbed from the rumen (Davis and Westfall 1972) and thus aspirin is unlikely to be very effective, even at doses as high as 100 mg/kg. Oral ibuprofen is well absorbed and an appropriate caprine dose may be similar to human doses on a mg/kg basis (DeGraves et al. 1993); however, this drug is not approved for food-producing animals in the United States. Flunixin meglumine is an irritating drug that is best given IV, but is also well absorbed orally (Konigsson et al. 2003) and has frequently been given by the SC route. This is the preferred non-steroidal drug for use in goats in the United States, because it is approved for other food animals (cattle and swine). A typical dose is 1.1-2.2 mg/kg once or twice a day. The extralabel use of non-steroidal anti-inflammatory drugs in cattle in the United States has been reviewed recently (Smith et al. 2008) and the same decision-making processes for drug selection are applicable for goats.
Preliminary studies for meloxicam in goats suggested a dose of 0.5 mg/kg IV repeated perhaps every 12 hours, because goats clear the drug rapidly (Hodgkinson and Dawson 2007; Shukla et al. 2007). However, this drug has become very popular for oral extralabel use in small ruminants in the United States in recent years.
One study found approximately 80% bioavailability by this route (Ingvast-Larsson et al. 2010). An oral dose of 1 mg/kg/day has been recommended for sheep (Stock et al. 2013). Because goats clear the drug more quickly than sheep, an oral loading dose of 2 mg/kg is followed by 1 mg/kg/day and then tapered if pain remains well controlled. In an acute case, a subcutaneous injection will provide a more rapid plasma peak than oral administration (Karademir et al. 2016).In other countries, preference might be given to IV or IM ketoprofen at 3 mg/kg daily (Arifah et al. 2003) or oral carprofen. The extralabel withdrawal times suggested by FARAD when ketoprofen is given to goats are 24 hours for milk and 7 days for meat (Damian et al. 1997). Carprofen has been used in England at an anecdotal dose of 50 mg once daily for dairy goats and at 20 mg daily for Pygmy goats. Another suggested carprofen dose is 1.4 mg/kg SC or IV, repeated once after 48-72 hours (Hodgkinson and Dawson 2007; Matthews 2016).