Validation of an intramuscularly-implanted microchip and a surface infrared thermometer to estimate core body temperature in broiler chickens exposed to heat stress

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Heat stress in poultry is associated with an increased core body temperature (CBT) which can be fatal. Methods of estimating CBT range from the minimally invasive method of inserting a digital thermometer into the cloaca of the bird, to the implantation of a temperature recording device (e.g. a data logger) in the peritoneal cavity, a method which gives the most accurate measure of CBT but may be considered invasive. To validate the use of less invasive alternatives to assess CBT in broiler (meat type) chickens using injectable devices, 12 birds were subject to surgery to implant a data logger deep in the body cavity and a microchip in the breast muscle. The birds were then placed in floor pens with an additional 36 birds and subsequently subjected to one of four simulated heat stress conditions over a 3-day period. Measurements of body temperature were collected at intervals from the data logger and microchip (CBT and IM-chip, respectively) along with taken under the wing, feet, comb and cloaca using an infrared thermometer. Changes in body temperature were calculated as the ΔT between pre heat stress and end of 3h heat stress each day. There was no relationship between CBT and IM-chip, but there was a significant correlation between ΔCBT and ΔIM-chip (R=0.71, P<0.05) during the heat stress. SBT measured under the wing correlated with CBT (R=0.71, P<0.05). Collectively these data confirm the suitability of intramuscularly-implanted microchip and strategically-positioned infrared thermometers to monitor CBT in birds exposed to heat stress, thereby replacing the invasive surgery and associated side-effects of deep body-implanted data loggers for the benefit of animal welfare.