4.2. Temperature measurements

Ambient temperature (T_a) (I–V), body temperature (T_b) (I–V) and leg temperature (T_leg) (III) were measured with copper-constantan thermoelements and recorded with a Yokogawa 3087 temperature recorder (I, II) or a Hewlett-Packard 34970A Data Acquisition/Switch unit connected to a PC (III, IV, V). Subcutaneous muscle surface temperatures from m. pectoralis were recorded in Japanese quail chicks with 0.7 mm copper-constantan thermoelements (TT-T-40, Omega, USA).

In domestic fowl chicks (Shaver), the development of body temperature and its diurnal rhythm was monitored from hatching for 43 days using 1.2 g XM-FH telemetric radio transmitters (Mini-Mitter Co., Sun River, USA). The transmitter contained an RC oscillator whose impedance and concomitant oscillation frequency was temperature dependent. The output frequencies of the transmitters were recorded using AM-receivers (RA-1000-TH, Mini-Mitter Co.) connected to a PC. The transmitters, sealed in plastic capsules and coated with wax (Elwax) for protection against moisture, were calibrated in water baths at 31.7°C and 38.9°C.

Newly-hatched domestic fowl chicks were anesthetized with an intramuscular injection mixture of ketamine 25 mg·kg^-1 (Ketalar®, Parke-Davis S.A., Barcelona, Spain) and xylatzine 2 mg·kg^-1 (Rompun®, Bayer AG, Leverkusen, Germany). The transmitters were implanted into the abdominal cavity through a small incision in the muscle layers of the abdomen. After implantation, chicks were placed to recover inside cages (60cm 40 cm 50 cm; length, width, height), each chick in a separate cage. Receivers were placed under the plastic floors of the cages. The cages were kept at a room temperature of 22°C. In one corner of each cage, a 150 W infrared lamp ensured a thermoneutral site inside the cage. After 12 h, three other chicks without transmitters were placed in each cage. The infrared lamps were gradually lifted as the chicks grew older. At the age of 21 d, two chicks without transmitters were removed from each cage.