Page 183 - The Welfare of Cattle

160 the WeLfare of CattLe

Gabapentin

Gabapentin is a γ-aminobutyric acid (GABA) analog historically used as an anti-seizure medi-
cation, but it has been recognized for its improvement in chronic, neuropathic pain. Gabapentin
works by decreasing excitatory neurotransmitter release as a result of modulation of voltage-gated
calcium channels. Additionally, analgesic activity is synergistically enhanced when used in con-
17
junction with an NSAID. 18,19

CaStratION

Castration is a common husbandry practice in the United States and Canada to minimize the
danger associated with intact males, unwanted pregnancies in feedlot situations, and improve car-
cass quality. The benefits of castration are widely known and deemed important to the cattle indus-
try. It is known that castration causes pain, distress, and other neuroendocrine changes to the animal
regardless of the technique used and age of animal. 20
The use of sexed semen is a practice to reduce the number of males born, especially in the dairy
industry. The use of sexed semen does come at a higher cost per unit of semen and lower conception
rates, but these cost may be offset by higher milk production in the lactation following carrying a
female calf. 21
The use of an immunocastration vaccine against gonadotropin releasing hormone (GnRH) has
been demonstrated to be an effective alternative for the physical castration of cattle. Although
22
attractive in principle, this technique has not gained widespread adaptation due to the need for
repeated injections, lack of approved products for cattle in the United States, and human health
implications of self-injection of the vaccine antigens. Therefore, physical castration methods are
primarily used for castration of cattle.
Pain and distress caused by castration is widely known, resulting in research looking into ways
to mitigate pain using pharmacologic agents. Commonly used drug classes include local anesthetics
such as lidocaine and NSAIDs such as flunixin meglumine, ketoprofen, and meloxicam.
Local anesthetics are beneficial in reduction of the acute pain associated with castration by
blocking the transmission of pain impulses to the central nervous system. A review of 15 castration
studies evaluating maximal cortisol concentrations indicated a 25.8% reduction of cortisol in cattle
receiving a local anesthetic compared to controls. Local anesthetics alone have minimal effects on
23
the overall feed consumption, average daily gain, and inflammatory mediators. 24–27
Investigations into the analgesic effects of flunixin indicate pain-relief during the initial period
post-castration. Flunixin administration is associated with pain-relief, although, in general, these
reported changes are not reported to persist beyond 8 hours. Cortisol concentrations were lower in
calves treated with flunixin following burdizzo clamp castrations and surgical castration compared
to castrated controls. 28,29 Furthermore, stride length increases when treated with flunixin and a
lidocaine or xylazine epidural. 30,31
In both surgically and non-surgically castrated cattle, preoperatively administered ketopro-
fen demonstrated reduced cortisol concentrations compared with castrated controls. 25–27,32 This
effect was potentiated when combined with a local anesthetic. Additionally, average daily gain is
23
improved by the administration of ketoprofen combined with a lidocaine local anesthetic for surgi-
26
25
cal but not non-surgical castration. Taken together with the cortisol data, when using ketoprofen,
multimodal therapy is needed for maximizing pain-relief during castration.
Calves administered carprofen following non-surgical clamp castration had lower cortical con-
centrations compared to untreated controls. Calves undergoing surgical castration had reductions
28
33
in cortisol concentrations, but these effects were not significant. Meloxicam has also been evalu-
ated in surgically and non-surgically castrated cattle. Administration of meloxicam to cattle before