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Cold-induced inhibition of thermal panting in shorn sheep 3. Effect of previous habituation to cold

  • J. Slee (a1)

Summary

1. Twenty-six shorn Scottish Blackface sheep received nine daily cold shocks (down to −10°C) each lasting 1 hr. This treatment reduced the metabolic response to cold (lower heart rates) and caused passive body cooling—defined as habituation. Eight selected sheep showing maximum habituation and 16 untreated controls then received blocking treatment (re-shorn and cooled for 2 hr at 18°C or 8°C) before being heat-stressed (at 42°C) to elicit panting.

2. Thermal panting, delayed as expected by blocking treatment, was further delayed by previous cold habituation. Habituated sheep blocked at 18°C panted 30 min later than blocked controls. In habituated sheep blocked at 8°C, panting was completely inhibited even after 90 min heat stress; their final mean respiration rate was 19/min v. 220/min in blocked controls and 250/min in unblocked controls. Rectal temperatures of habituated sheep were lower than controls during blocking treatment.

3. Habituation, by restraining the normal metabolic response to cold, increased the heat debt during blocking treatment and lessened the heat load during subsequent heat stress. This apparently reduced the drive for panting. Habituation may also have favoured a direct inhibitory effect of cold on the respiratory centres.

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References

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Bligh, J. 1963. Inhibition of thermal polypnoea in the closely shorn sheep. J. Physiol. 168: 764781.
Slee, J. 1972. Habituation and acclimatization of sheep to cold following exposures of varying length and severity. J. Physiol. 227: 5170.
Slee, J. 1973a. Cold-induced inhibition of thermal panting in shorn sheep. 1. Effect of intensity of cold exposure. Anim. Prod. 16: 271283.
Slee, J. 1973b. Cold-induced inhibition of thermal panting in shorn sheep. 2. Effect of previous acclimatization to cold. Anim. Prod. 17: 919.
Slee, J. and Sykes, A. R. 1967. Acclimatization of Scottish Blackface sheep to cold. 1. Rectal temperature responses. Anim. Prod. 9: 333347.
Sykes, A. R. and Slee, J. 1968. Acclimatization of Scottish Blackface sheep to cold. 2. Skin temperature, heart rate, respiration rate, shivering intensity and skinfold thickness. Anim. Prod. 10: 1735.
Sykes, A. R. and Slee, J. 1969. Cold exposure of Southdown and Welsh Mountain sheep. 2. Effects of breed, plane of nutrition and previous acclimatization to cold upon skin temperature, heart rate, shivering and respiration rate. Anim. Prod. 11: 7789.

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