Some physiological responses of imported dorset sheep as observed in the shade

S. Abdul Wahid

Abstract

Ewes of purebred Dorset Horn (DH) and Polled Dorset (PD) (both imported from New Zealand), and indigenous sheep of Malaysia (ISM), five of each breed, were used to study the adaptation of the imported Dorset breeds to the Malaysian tropical climate. After ten days of initial adjustment in the shade, rectal temperature, respiration rate and pulse rate were recorded at 0800 hours and 1400 hours daily for three days. Environmental air temperature and relative humidity were also recorded. The results showed that the morning and afternoon rectal temperatures of PD, DH and ISM were 39.23±0.32⁰C and 39.57±0.40⁰C, 38.94±0.25⁰C and 39.27±0.27⁰C, and 38.7±0.45⁰C and 39.27±0.31⁰C which were within the normal range of 39.0±1.5' Celsius. The rectal temperature increased with the increase in environmental air temperature in the afternoon. This was followed by an increase in respiration rate which was a sign of high heat load, particularly in exotic breeds. The pulse rate of PD increased significantly (P <0.05) and the increase was highly significant( P<0.01) in DH and ISM sheep. In the afternoon, the values of Benezra's index of adaptability (BIA) were higher in both imported breeds as compared with that of ISM (6.70 and 6.79 vs 3.85) while the Rhoad's coefficients of heat tolerance (RCHT) for PD (89.80) and ISM (94.00) were lower than that of DH (95.20) which indicated that PD had lower capability than DH in adapting to local environment even under the shade.

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