Short CommunicationOnset, duration and efficacy of four methods of local anesthesia of the horn bud in calves
Introduction
Dehorning is a routine practice in cattle production. Previous studies have shown that dehorning is painful and that local anesthesia mitigates acute pain (Morisse et al. 1995; Grøndahl-Nielsen et al. 1999; Stafford & Mellor 2005; Stewart et al. 2009; Graf & Senn 1999). The cornual nerve block is currently the accepted technique to anesthetize cattle horn prior to removal (Grøndahl-Nielsen et al. 1999). Some studies have combined the cornual block with a ring block to increase the probability of effective anesthesia (Faulkner & Weary 2000). To our knowledge, the efficacy, onset and duration of action of the cornual nerve block has not specifically been evaluated.
Recent advances in drug delivery technology have resulted in needle-free techniques (JET) for intradermal and subcutaneous drug delivery. JET uses a high-velocity stream of fluid to pierce the skin and deliver drugs into the intradermal, subcutaneous or intramuscular spaces (Schramm Baxter & Mitragotri 2004). JET has many potential advantages over needle injections including decreased; pain on delivery, biohazardous waste, tissue trauma and risk of infection.
An eutectic mixture of local anesthetics (EMLA) is used as a topical anesthetic in people undergoing minor medical procedures (Buckley & Benfield 1993). EMLA (Astra-Zeneca Canada Inc., Ontario, Canada) cream contains 2.5% lidocaine and 2.5% prilocaine and application 1–5 hours before a procedure is recommended. EMLA cream could provide a simple, safe method of anesthesia of the horn bud in calves.
The objective of this study was to examine four local anesthetic techniques: cornual nerve block, ring block, percutaneous jet injection and topical EMLA cream, for anesthesia of the horn bud in calves. Efficacy, onset time and the duration of anesthesia were evaluated.
Section snippets
Study design
Eight, 2 month-old male Holstein Friesian calves (65–90 kg) were used in a randomized crossover study. One the first day of the study, calves were randomly assigned to receive one treatment (1–4). On subsequent weeks, calves would receive the next numbered treatment so that each calf received all four treatments with 7 days ‘washout’ between treatments. Calves were purchased from two local farms and individually housed for 2 weeks before the study. The calves had free access to water, calf
Anesthetic treatments
On each treatment day, calves received one of four treatments:
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Cornual nerve block (C) – 5 mL lidocaine 2% with epinephrine (0.01 mg mL−1) (Lido-2; Rafter 8 Products, Alberta, Canada) was injected under the skin midway between the horn bud and the lateral canthus of the eye, ventral to the frontal crest, using a 20-gauge 2.5 cm needle. Four mL was injected at this location, after ensuring the needle was not in a blood vessel, and the remainder was infiltrated through the tissues on withdrawal
Results
The median baseline positive avoidance response to stimulation was level 6 for all treatment groups. Seven C calves (87.5%), eight R calves (100%), and three JET calves (37.5%) developed cutaneous anesthesia of the horn bud. Topical EMLA cream failed in all calves. In the calf with the failed block in treatment C, cutaneous sensation was mapped using needle prick around the horn bud. This calf had a localized area of sensation at the caudolateral aspect of the horn bud. 6/8 C, 5/8 R and 2/3 JET
Discussion
Two novel techniques of anesthesia, JET and EMLA, of the horn bud were evaluated in this study, and neither was found to be effective. Failure of the JET injection was likely due to poor anesthetic penetration or inadequate drug concentrations around the cornual nerve. Some injections failed to inject all the lidocaine through the skin. In people, ‘wet’ injections can result from a characteristic in the design of the device, use of the device, variations in skin morphology, or some interaction
Acknowledgement
This research project was funded through the Margaret Gunn Endowment Fund.
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