Research/PIC Project 192
From Poultry Hub
Project title: Non-invasive tests of stress in laying hens. (Canadian Poultry Magazine November 2008)
Project Leader: Dr. Nigel Cook
Organisation: Alberta Agriculture and Rural Development
Contents |
Project overview
Issues of animal welfare and assurance of care are areas of growing public interest. Assessment of laying hen welfare is often based on behavioural observations or physical indications of abnormal behaviour such as feather loss due to feather pecking. It is well recognized that the assessment of animal welfare should involve, as far as possible, a comprehensive approach that includes physiological measures of biomarkers indicative of stress. Having such comprehensive assessment strategies in place can aid the industry in making objective decisions about the welfare of poultry in any given system. A commonly used biomarker of stress in all species is the measurement of corticosteroid hormones. In avian species, the hormone measured is usually corticosterone. This is difficult to measure via blood sampling, however, since the sampling itself requires handling the birds, which stresses them. It is difficult to validate corticosterone levels in alternative sample media such as feces or eggs for the same reason, since these must be compared to circulating levels in the blood to determine if they are accurately reflect circulating corticosterone levels. To date, the appropriateness of eggs and excreta to assess stress levels in birds has not been fully validated. Read full report
The Research
To overcome this problem of acute stress during blood sampling in order to validate these measures, Dr. Nigel Cook at Alberta Agriculture and Rural Development, and his research team, utilized a method to collect blood without handling the birds. They inserted a catheter which allowed for blood collection from birds that are able to move freely within their cages, undisturbed. In order to determine how much maternal corticosterone is transferred to the egg albumin, yolk and excreta, radioactively tagged corticosterone was incorporated into these components in a time-dependent manner. The amount of hormone transferred to egg albumin and yolk was very small (<1%) compared to the amounts in excreta. In a second experiment, stimulated increases in blood corticosterone levels were manifested in increased total daily excreta corticoid concentrations in same-day samples. However, no significant relationships were found between the measures of plasma responses to stimulation and total daily excreta levels of corticoid metabolites. Total daily excreta corticoid levels were more closely associated with plasma baseline adrenocortical activity than to stimulated levels. Excreta levels are related to clearance rates and therefore may negatively correlate with acute responses in blood. Caution should be used in the interpretation of excreta measurements of corticosteroids in relation to acute stress responses. This relationship may provide a tool for studying responses to chronic stress. However, it should be recognised that measurement of excreta corticoids as a biomarker of adrenocortical activity has severe limitations. Most notably, the timing of sample collection is crucial to capturing acute adrenocortical responses, and the confounding effect of variations in clearance rates among individual birds could lead to misinterpretation of excreta corticoid concentrations. These studies demonstrated transfer of endogenous maternal corticosterone to egg albumin and yolk. However, there was no evidence of a relationship to a stimulated increase in blood levels of corticosterone. There was a significant correlation between albumin and yolk levels within individual eggs. The concept of an increasing gradient in yolk corticosterone levels from the centre to the outer layers of the yolk was demonstrated.However, these studies do not support the measurement of albumin or whole yolk corticosterone concentrations as biomarkers of acute adrenocortical responses to stimulation, or maternal stress responses. Read full report
The Bottom Line
The relationships between egg albumin, yolk and excreta measurements to unstimulated plasma corticosterone levels suggests that these measures may reflect adrenocortical responses to longer term, chronic stress, but further research and validation of this concept would be required. Read full report
Source
Poultry Industry Council
- 483 Arkell Road, Guelph, Ontario,Canada, N1H 6H8.
- pic@poultryindustrycouncil.ca
- http://www.poultryindustrycouncil.ca
