Marked for Success?
The US Department of Agriculture Livestock Behavior Research Unit's Dr. Heng-Wei Cheng and graduate researchers Rachel L. Dennis and Alan G. Fahey study the impact of identification on poultry welfare.
Artificial marking and tagging for identification purposes is integral to animal research, including the utilization of animals as models for biomedical, agricultural and wildlife experimentation. A variety of identification systems is available, and researchers often choose a method based on experimental design or convenience. Examples include tags containing data about the individual or marks that can be seen from a distance, with little known of their effects on the animals or experimental results. Our research group investigated the potential side effects of four popular identification systems used in poultry research. The birds' behavioral and physiological changes associated with leg bands, wing bands, neck tags and livestock marker applied to tail feathers were examined in comparison with birds bearing no identification. The study was supported by funding from an Animal Welfare Institute Refinement Award.
Laying hens were marked with one of the four identification systems, and each bird was housed with an unmarked cage-mate. Unmarked birds were paired for one hour a day with birds of each marking or tagging treatment, to create every possible pairing. During one-hour tests, the birds' behaviors were recorded and analyzed for aggression and feather pecking. None of these markings had any effect on aggressive behaviors given or received by the bearers. Interestingly, the frequency of feather pecking increased in wing-banded birds, which may suggest that wing banding birds raises social stress levels.
Two days after the completion of behavior testing, physiological measures were taken. One measurement was for fluctuating asymmetry, which is the degree of asymmetry of an ideally symmetric trait. Birds (and other animals) can become more asymmetric because of multiple factors, including social or environmental stress. By examining the fluctuating asymmetry of the birds' shank lengths and widths, we found leg- and wing-banded birds were more asymmetric than unmarked birds, which could be due to increased social stress. Leg-banded birds also had a reduced growth rate over the testing period compared with birds bearing all other identification marks. A slower growth rate may be a result of monopolization of resources by more dominant birds, an increased metabolism, or decreased appetite due to elevated stress.
The "stress hormone" corticosterone is released from the adrenal gland in response to various stimuli. One of its main functions is to maintain physiological homeostasis, or stability in response to stress. Results showed that corticosterone levels were similar in all birds, except for wing-banded birds, who had a much lower level. This could be related to chronic social stress, resulting in the reduced reactivity of their adrenal glands. On the other hand, compared to other birds, immune function was suppressed in leg-banded birds, as demonstrated by a reduced concentration of heterophils—a type of white blood cell that provides protection against infection. Our findings show that wing and leg banding systems have a greater impact on certain stress parameters.
These results have important implications for poultry and other animal research. Wing and leg bands are identification systems used commonly in research and are often thought to be less visually conspicuous than tag or marking systems since they are difficult for a human observer to see from a distance. However, our findings suggest that these marking systems may be more conspicuous to birds and other animals. Wing and leg band systems may also have an effect on movement or comfort of the marked birds, as these systems utilize a heavier metal base that may irritate skin and hinder movement, since they are located near a commonly used limb joint.
Without consideration of how these systems alter birds' physiology and behavior, these identification systems could lead to misinterpretation of experimental results and have a negative impact on the integrity of animal research. Although the cellular mechanisms are not yet clear as far as which identification systems alter birds' physiological and behavioral parameters, our findings suggest a species-specific approach to marking is required.