Nigel J. Cook

Review: Minimally invasive sampling media and the measurement of corticosteroids as biomarkers of stress in animals

Cook, N. J. 2012. Review: Minimally invasive sampling media and the measurement of corticosteroids as biomarkers of stress in animals. Can. J. Anim. Sci. 92: 227-259. The measurement of corticosteroid hormones is commonly used as a biomarker of an animals response to stress. The difficulties in obtaining blood samples and the recognition of the stressor effect of blood sampling are primary drivers for the use of minimally invasive sample media. In mammals these include saliva, feces, urine, hair, and milk. In birds, samples include excreta, feathers, egg yolk and albumin. In fish, corticosteroids have been measured in excreta and swim-water. Each of these sample media incorporate corticosteroids in accordance with the processes by which they are formed, and this in turn dictates the periods of adrenocortical activity that each sample type represents. Cortisol in saliva represents a time-frame of minutes, whereas the production of feces may be hours to days depending on the species. The longest time-integrations are for hair and feathers which could be over a period of many weeks. The sample media also determines the structural changes that may occur via processes of conjugation to glucuronides and sulfides, metabolic conversion via enzymatic action, and bacterial breakdown. Structural changes determine the optimum methodologies used to measure corticosteroid hormones. In most sample media, measurement of a specific corticosteroid is a requirement depending on the species, e.g., cortisol in most mammals, or corticosterone in birds. However, in samples involving products of excretion, methodologies that measure a broad range of structurally related compounds are probably optimal. The utility of minimally invasive sample media as biomarkers of stress responses depends on the degree to which the corticosteroid content of the sample represents adrenocortical activity. Commonly, this involves comparisons between corticosteroid concentrations in blood plasma with concentrations in the alternative sample media. This review focuses on the methodological and biological validation of corticosteroid measurements in minimally invasive samples as biomarkers of adrenocortical responses to stress.

Infrared thermography detects febrile and behavioural responses to vaccination of weaned piglets

An automated, non-invasive system for monitoring of thermoregulation has the potential to mitigate swine diseases through earlier detection. Measurement of radiated temperature of groups of animals by infrared thermography (IRT) is an essential component of such a system. This study reports on the feasibility of monitoring the radiated temperature of groups of animals as a biomarker of immune response using vaccination as a model for febrile disease. In Study A, weaned pigs were either treated with an intramuscular vaccine (FarrowSure Gold), a sham injection of 0.9% saline or left as untreated controls. An infrared thermal camera (FLIR A320) was fixed to the ceiling directly above the pen of animals, and recorded infrared images of the treatment groups at 5 min intervals. The effect on temperature of the spatial distribution of pigs within the pen was significant, with higher temperatures recorded when pigs were grouped together into a single cluster. A higher frequency of clustering behaviour was observed in vaccinated animals compared with controls during a period of the afternoon ~4 to 7 h post-vaccination. The daily mean of the maximum image temperature was significantly higher in vaccinated animals compared with control and sham-treated animals. In the vaccination treated group, the 24 h mean of the maximum temperature was significantly higher during the post-vaccination period compared with the 24 h period before vaccination. Increased temperature in the vaccinated animals occurred from ~3 h, peaked at ~10 h, and remained elevated for up to 20 h post-vaccination. In Study B, the effect of prevalence was tested in terms of the difference in maximum temperature between control and vaccination days. A thermal response to vaccination was detected in a pen of 24 to 26 animals when <10% of the animals were vaccinated. The results support the concept of radiated temperature measurements of groups of animals by IRT as a screening tool for febrile diseases in pig barns.

Dexamethasone reduces transport-induced weight losses in beef calves

Dexamethasone was administered intramuscularly at two dose levels (Trial 1 = 0.088 mg kg-1; Trial 2 = 10 mg per calf) to beef calves (Trial 1, n = 60; Trial 2, n = 58) prior to transport by road for 10 and 8 h, to test the effect on transport-induced weight losses. Calves lost significant weight over the transport periods (P < 0.001) but dexamethasone-treated calves lost significantly less weight than control animals (P < 0.004). The relationship between salivary dexamethasone concentrations and weight losses in Trial 1 exhibited a significant trend (r = 0.47, P < 0.06). The correlation of administered dose of dexamethasone (mg kg-1) with weight losses in Trial 2 was significant (r = 0.5, P < 0.006). Dexamethasone administration prior to long-haul transport reduced transport-induced weight losses, and may be an effective method of mitigating transport stress.Key words: Transport, beef calves, dexamethasone, weight losses, salivary cortisol, salivary dexamethasone

Minimally-invasive assessments of the behavioural and physiological effects of enriched colony cages on laying hens

The well-being of laying hens in cages of 5, 10, 20 and 40-birds/cage, and enrichment with perches, nest boxes and scratch pads, was assessed using behavioral and physiological parameters. Laying hens were Lohmann Brown (n = 360) and White Leghorns (n = 360), housed from 17 to 65 weeks of age. Behavioral parameters were; the percentage of birds per cage roosting on perches, claw length (n = 288), and the percentage of eggs laid within nest boxes. Physiological parameters were; the assessment of feather cover from measurements of radiated temperatures by infrared thermography (IRT), bone mineral content of the humerus and femur by quantitative computer tomography (QCT) scans, and adrenocor- tical function as a marker of chronic stress by measurements of corticosterone concentrations in egg yolk and albumin. The majority of eggs (72.7 %) in furnished cages were laid in nest boxes. Nest use was highest in Brown hens (P 80 %, but significantly less in the 10-bird cages (P < 0.0012) due to a shorter perch length. Claws were shorter on birds in cages with scratch pads (P < 0.0001). Feather insulation declined from 35 to 60 weeks of age for breast and back areas (P < 0.0001). White birds exhibited superior breast feather insulation compared to Brown birds. Egg albu- min corticosterone levels declined between 35 and 60 weeks of age (P < 0.011). There were no indications of an affect of colony size or cage enrichment on measurements of bone mineral content. The findings indicated a preference for the use of nest boxes, perches and scratch pads. Significant losses in feather insulation occur with time. A reduction in egg albu- min corticosterone levels over time may be a marker of chronic stress in caged laying hens.

The collection of multiple saliva samples from pigs and the effect on adrenocortical activity

Cook, N. J., Hayne, S. M., Rioja-Lang, F. C., Schaefer, A. L. and Gonyou, H. W. 2013. The collection of multiple saliva samples from pigs and the effect on adrenocortical activity. Can. J. Anim. Sci. 93: 329-333. The validity of collecting multiple saliva samples for the measurement of cortisol was tested in two sampling regimes in two weight classes of grower pigs (50 and 100 kg). The sampling regimes were a high-frequency, short-duration (HFSD) protocol involving collection of multiple samples within approximately 2 min of each other over a period 30 min. The second regime was a low-frequency, long-duration (LFLD) protocol in which samples were collected every 30 min for 3 h. Both sampling regimes were applied to individually housed pigs. The effect of repeated sampling of a focal pig on its cohorts in a group-housed pen was tested using the LFLD regime. There was no evidence of an effect of either of the sampling protocols on salivary cortisol concentrations in individually housed or group-housed pigs. There was some evidence that higher concentrations of salivary cortisol were associated with longer individual sampling durations in the HFSD regime for animals in the 50-kg weight class but not in the 100-kg weight class. The evidence from these experiments indicates that the collection of multiple saliva samples does not affect salivary cortisol concentrations in grower pigs, but that collection of individual samples in as short a time as possible would be prudent to avoid sampling effects in younger animals.

The automated analysis of clustering behaviour of piglets from thermal images in response to immune challenge by vaccination

An automated method of estimating the spatial distribution of piglets within a pen was used to assess huddling behaviour under normal conditions and during a febrile response to vaccination. The automated method was compared with a manual assessment of clustering activity. Huddling behaviour was partly related to environmental conditions and clock time such that more huddling occurred during the night and at lower ambient air temperatures. There were no positive relationships between maximum pig temperatures and environmental conditions, suggesting that the narrow range of air temperatures in this study was not a significant factor for pig temperature. Spatial distribution affected radiated pig temperature measurements by IR thermography. Higher temperatures were recorded in groups of animals displaying huddling behaviour. Huddling behaviour was affected by febrile responses to vaccination with increased huddling occurring 3 to 8 h post-vaccination. The automated method of assessing spatial distribution from an IR image successfully identified periods of huddling associated with a febrile response, and to changing environmental temperatures. Infrared imaging could be used to quantify temperature and behaviour from the same images.

Assessing Consistency in Radiated Thermal Output of Beef Steers by Infrared Thermography

Measurements of radiated thermal output are claimed to reflect the metabolic efficiency of mammals. This is important in food-producing animals because a measure of metabolic efficiency may translate to desirable characteristics, such as growth efficiency or residual feed intake, and permit the grouping of animals by metabolic characteristics that can be more precisely managed. This study addresses the question of whether radiated thermal parameters are characteristic of individual animals under normal and metabolically-challenging conditions. Consistency in radiated thermal output was demonstrated over a period of four weeks on condition that a sufficiently representative sample of measurements could be made on individual animals. The study provided evidence that infrared thermography could be used as an automated, rapid, and reliable tool for assessing thermoregulatory processes.