Thermal Perches as Cooling Devices for Reducing Heat Stress in Caged Laying Hens
Heat stress (HS) is one of the most detrimental environmental stressors that affect poultry. Many egg companies are located in tropical and subtropical areas where HS is a year round problem. Global climate change is causing more hot days and frequent unexpected heat waves. Animal health and welfare status are greatly compromised under high ambient temperatures. In laying hens, HS negatively affects livability, egg production, shell quality, and the internal quality of eggs. Induced molting, used to rejuvenate flocks, is a common managerial practice that extends the productive life of egg laying flocks. Molting brings the flock into a second cycle of lay with improved eggshell quality. Induced molting and elevated temperatures are well-defined stressors. Hens subjected to an induced molting during hot weather may find it difficult to cope with both stressors simultaneously. Enriched colony cages, furnished with perches, a nest box, and scratch pads, are the preferred housing system based on hen health and welfare, egg production parameters, and environmental impact. The perches installed inside cages not only meet the hen’s behavioral desire to roost but also improves skeletal integrity through increased activity. In addition, the key amenity of perch in enriched cages could be modified as a cooling device to improve hen thermal comfort. Our objective was determine if water cooled perches (CP) could ameliorate the detrimental effects of HS on caged laying hens when subjected to daily cyclic heating episodes during egg laying and molt. The provision of CP during 2 daily cyclic heating episodes administered from 21 to 35 and 73 to 80 wk of age ameliorated the negative effects of HS on caged laying hens. Conductive heat was transferred from the hen’s feet and her other body parts to the chilled water in the perch pipe allowing for more effective heat dissipation. Hens with access to CP had improved egg production, body weight, livability, egg weight, and eggshell quality traits without influencing the percentage of dirty and cracked eggs, overall plumage condition, and foot health compared to the other 2 treatments of air perch (AP) or control with no perch (CTRL). The CP hens were also able to maintain their body core temperature more effectively with increased metabolic rate as evidenced by higher triiodothyronine concentrations and triiodothyronine to thyroxin ratio. The stress response in the CP hens was also alleviated as indicated by a reduced heterophil to lymphocyte ratio. Less circulating heat shock protein 70 in the CP hens indicated that denatured-associated protein damage was less problematic under conditions of HS. Hens were subjected to a 28 d molt when they were 85 to 88 wk of age, consuming a diet of 71% wheat middling and 23% corn diet. During molt, they were also exposed to a reduced photoperiod with daily cyclic heat. The provision of CP assisted hens with better adaptation to the stresses of an induced molt during heat exposure, resulting in an optimum regression of the reproductive system and improved post-molt egg production without impairing egg and shell quality. Providing hens with access to CP as compared to AP had little effect on musculoskeletal health or immunological and neurophysiological traits 22 wk after the application of HS and the completion of the molt. Differences among treatments were mainly due to the perch rather than the cooling of the perch as the responses of CP and AP hens were similar. Perches, regardless of whether they were cooled or not, caused greater muscle deposition and wing bone mineralization as well as lower homovanillic acid/dopamine turnover. Intervening with CP access, however, did prevent the heat- and molt-induced reduction in absolute liver and spleen weights as compared to the AP or CTRL hens. In conclusion, CP was an effective cooling method for caged laying hens. They ameliorated the deleterious effects of HS by improving the efficacy of an induced molt under conditions of daily cyclic heat with improved post-molt egg production.
Hester, Purdue University.
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