Adoption of immobility by shackled broiler chickens: effects of light intensity and diverse hooding devices

• Published in: Applied animal behaviour science Vol. 55; no. 3; pp. 327 - 335
• Main Authors: Jones, R.Bryan, Hagedorn, Teresa K., Satterlee, Daniel G.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 1998
• Subjects: BEHAVIOUR; BROILER CHICKENS; Chicken-welfare; COMPORTAMIENTO; COMPORTEMENT; ESTRES; Hoods; LIGHT; Light intensity; LUMIERE; LUZ; Patterned vision; POLLO DE ENGORDE; POULET DE CHAIR; STRESS; Struggling; Tactile contact; VISION; Visual input; Patterned vision; Chicken-welfare; Visual input; Struggling; Light intensity; Tactile contact; Hoods
• ISSN: 0168-1591; 1872-9045
• DOI: 10.1016/S0168-1591(97)00048-8

Chickens often struggle violently and injure themselves when they are suspended from shackles, a practice which is commonly used when farmers or veterinarians need to examine representative birds from the flock. Covering the heads of restrained chickens and other birds with a hood is thought to strengthen immobility reactions but the influential variables were poorly understood. The present study measured struggling, vocalization and respiration in broiler chickens which were inverted and suspended from shackles in one of a number of test situations. In Experiment 1, 42-day-old, non-hooded broiler chickens were shackled individually at one of four light intensities (< 2, 5, 50 or 200 lux). This allowed us to determine if low light levels per se were sufficient to minimize struggling. In Experiment 2, 45-day-old broilers were shackled in daylight (250–300 lux) following the application of an opaque cotton hood, a transparent nylon net hood, or a simple drawstring fastened around the neck. Non-hooded birds served as controls in Experiment 2. The studies yielded four main findings. Firstly, neither the vocal nor the struggling responses of non-hooded, shackled broilers were influenced by substantial variations in ambient light intensity. Secondly, struggling and vocalization were virtually eliminated if the birds' heads were covered with an opaque hood before shackling; these findings confirmed our previous observations. Thirdly, although the opaque hood was the most potent device, both a transparent hood and a drawstring fitted around the neck also promoted the adoption of silence and immobility. Fourthly, there were no detectable treatment effects on respiration rate and, hence, presumably, on the ease of breathing. Collectively, the present findings suggest that both the tactile properties of hoods and their components as well as their ability to impair patterned vision contributed to the adoption of immobility by shackled broiler chickens, but that the latter variable was the most influential. The strategic relevance of the present findings is discussed in terms of the welfare, not only of chickens shackled at the farm for examination, but also of the staff at processing plants.