The effects of elevated temperature and humidity on rectal temperature and respiration rate in the New Zealand white rabbit

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Abstract
In 2 replicated factorial experiments, 7-h climate chamber exposures were used to study the responses of adult NZW rabbits to a range of elevated temperatures and humidities. At 18 mm Hg water vapour pressure, 23.8° C was well tolerated, rectal temperature (RT) and respiration rate (RR) averaging 38.6±0.3° C and 82.9±15.5 breaths/min, respectively. Both parameters were elevated (PP<0.05). Thereafter both parameters increased progressively, but with no significant differences between successive recording periods, until RR reached 550.3±88.8/min at 41.7° C RT. Humidities of 25, 29 and 33 mm Hg water vapour pressure were, on the other hand, classified as “wet” and were tolerated for only 92±22, 81±16 and 119±50 min, respectively. RR at the times that RT reached 41.7° C at these 3 humidities was 732±26, 789±30 and 764±23/min, respectively. The results point to the likelihood that thermal stress will adversely affect the productivity and welfare of NZW rabbits in the tropics unless adequate housing environments are provided. Significant between-individual phenotypic differences in heat tolerance suggest the need for genetic studies of the possibility of selecting for improved heat tolerance.