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Feasibility and reliability of pressure algometry for mechanical nociceptive threshold quantification in lambs in a
Charlotte Helen Johnston1, Danila Marini2,3, Stefan T Musolino1,4
1School of Biomedicine, Faculty of Health and Medical Sciences, University of Adelaide, Australia, Adelaide, SA, Australia.
Objective:
To validate a modified algometer method for assessing mechanical nociceptive threshold (MNT) in lambs before and after husbandry procedures (marking) under field conditions by testing the precision, intra-operator reliability and agreement, and minimal detectable change (MDC).
Animals:
Forty-six randomly allocated Merino lambs: 6 control (sham handled), 13 hot knife tail docked, 13 rubber ring tail docked, 7 hot knife tail docked and rubber ring castrated, and 7 rubber ring tail docked and castrated.
Methods:
MNT (mean triplicate measurements at each replicate) was assessed at the tail base, using three replicate measurements before, and three hours after marking to assess precision, reliability, agreement, and MDC. A single operator performed all testing, with lambs restrained by one of three handlers (randomly) for each replicate. Within-animal/-occasion (pre- or post-marking) relative and absolute precision were evaluated using the coefficient of variation (CV) and a combination of standard deviation (SD) and dispersion modelling, respectively. Agreement was assessed using Bland-Altman plots, and linear mixed effects regression was used to determine the intra-class correlation coefficient (ICC) for intra-operator reliability, and any systematic effects of replicate order or handler. MDC was calculated from the standard error of measurement. Responsiveness to marking was analyzed by comparing MNT change from pre- to post-marking using linear mixed effects regression.
Results:
The overall median MNT was 3.07 kgf (IQR = 2.00-3.84, range = 1.23-5.00). Greater body weight was associated with significantly higher absolute imprecision (p = 7 × 10-5). Median CV was 12.5% (IQR = 7.29-18.16, range = 1.5-55.4) and was significantly higher post-marking (p = 0.0003), likely related to lower post-marking MNT. The agreement between replicates was good with small mean differences (0.02-0.26 kgf), although there were wide Bland-Altman limits of agreement (2.27-3.51 kgf). There was good intra-operator reliability [ICC (95% CI) = 0.83 (0.81-0.94)]. The minimum detectable change was 1.38 kgf. There was a significant reduction in MNT after marking for all marking groups (p < 0.01).
Conclusions:
Modified algometer MNT measurement in lambs around the time of marking was feasible with sufficient precision and responsiveness to demonstrate a reduction in nociceptive threshold following husbandry procedures.
