Seasonal changes in physiological responses and energy expenditure of sheep maintained on semi-arid pasture

Abstract

A study on the energy expenditure of sheep was carried out at the Central Sheep and Wool Research Institute, India during August 1995 to July 1996 by conducting two experiments: one on tracheal cannulated rams maintained on stall-feeding in autumn 1995 (Expt 1) followed by year-round grazing on silvipasture (Cenchrus ciliaris pasture interspersed with fodder trees) over three seasons: monsoon, winter and summer, 1995/96 (Expt 2). Physiological responses and energy expenditure measurement of housed and grazing sheep were recorded at 06.00, 14.00 and 22.00 h for 5 consecutive days in each season. Tracheostomized sheep harness with meteorological balloon were used for collection of expired air and measurement of energy expenditure. Rectal temperature (RT) of sheep at 06.00 h was similar in all the seasons except for a significant (P<0·05) lower value in monsoon. The rise of RT from 06.00 to 14.00 h in grazing animals was 1·6 °C, higher than that in housed sheep (0·9 °C). Skin temperature (ST) was least in winter and highest at 14.00 h in the monsoon and autumn seasons. Respiration rate (RR) showed a marked rise at 14.00 h in all the seasons. The heart rate (HR) of grazing sheep was higher, irrespective of season, at 14.00 h. At 06.00 and 22.00 h, the heart rate was higher in winter and summer than in the monsoon season. Overall energy expenditure (EE) was 4·85 MJ/24 h during winter which increased to 5·85 MJ/24 h in summer and 6·70 MJ/24 h in the monsoon. The mean rise in energy expenditure per °C rectal temperature in all the seasons was 338 kJ/kg W0·75. Comparable mean values per 10 °C ambient temperature and 10 °C black globe temperature were 404 and 173. The increase in energy expenditure of grazing compared to housed sheep in monsoon, winter and summer was 78, 15 and 33 % respectively. The mean value was +43%.