An investigation of pressure algometry and thermal sensitivity tests for assessing pain associated with a sow lameness model and calf disbudding
The first objective for this thesis was to examine mechanical, including pressure algometry (PA) and von Frey filaments (VF), and thermal sensitivity (TS) nociceptive tests as objective non-invasive measures of pain in swine and cattle. The second objective of this study was to examine novel pain mitigation agents to alleviate pain in swine and cattle.
The first research study assessed the validity of mechanical and thermal nociceptive tests by analyzing differences in nociceptive threshold in cull sows when sound, for baseline values, and when induced-lame in one hind leg. This lameness study also assessed sodium salicylate and flunixin meglumine (Banamine ®) as analgesic treatments for pain associated with lameness. Results from this study indicate that PA is a valid non-invasive method to objectively quantify the mechanical nociceptive threshold (MNT) prior to lameness induction, as well as when sows were induced-lame in one hind leg. This test was valid because no differences were detected between the sound and designated lame hind leg prior to induction, and reduced MNTs were observed on the induced lame limb post induction. No improvement was detected with either analgesic treatment as assessed with PA. Due to the high variability in TS latencies from sound to lame leg at all trial days, TS was not a valid pain assessment tool in this sow lameness pain model.
Objectives for the calf disbudding research were to evaluate VF and TS for assessing disbudding pain in calves relative to PA, which has been previously validated as an objective pain test in a cautery disbudding pain model. Pressure algometry was also utilized to objectively determine the effectiveness of ethanol or a depot formation of lidocaine for extended analgesia during disbudding relative to a control lidocaine cornual nerve block. In this experimental design, neither VF nor TS pain tests were practical pain assessment tools. Results from PA indicated that the ethanol anesthetized calves displayed elevated MNTs relative to the control calves, and depot-treated calves tolerated reduced MNTs relative to the control from +1 hour post-disbudding through +83 hours post-disbudding, which indicates that ethanol provided extended anesthetic relief, and that this depot formation of lidocaine is not a suitable anesthetic treatment for cautery disbudding calves.
In conclusion, this research has validated the use of PA as an objective pain assessment tool for both a transient-induced sow lameness and a cautery disbudding pain model. Results from these studies provide promising evidence as to the range of research capabilities offered by PA. In both experimental models, TS was not an appropriate measure of nociception. Further research and refinement is required for this TS test to be applicable in a transient-induced sow lameness and calf cautery disbudding pain model.