Study of Shearing Effect on Performance and Some Physiological and Metabolic Parameters in Dalagh Lambs under Ambient Heat Stress

Abstract
The aim of the study was to investigate the effect of shearing on performance and some metabolic and physiologic parameters in fattening lambs under heat stress. Sixteen male, fattening Dalagh lambs (3.5±0.5 months of age) were divided into two groups and maintained individually for adaptation. One group was completely shorn and another left unshorn. Duration of the study was four consecutive weeks after the shearing. Weight changes were recorded weekly and feed intake was measured three times a week. Rectal temperature, heart rate and respiratory rate were weekly measured. Blood samples were collected and used for blood metabolites and hormones' determinations. Results showed that shearing had no significant effects on feed intake and weight gain over the study. Feed conversion ratio was improved (P<0.05) by the shearing (10.70 vs. 13.26). Shearing caused a non-significant decline in rectal temperature (P>0.05). Heart rate was not affected by the shearing, but respiratory rate was significantly decreased (P<0.05) in shorn lambs (137.59 vs. 159.50 breaths/min). Blood glucose, urea and total protein levels were not affected by the shearing. Blood cortisol level was not significantly different between groups, but the shearing resulted in a marked decline in blood thyroxine level (P<0.05). The marked decline in respiratory rate and relative decline in rectal temperature by the shearing indicate a lowered response to heat stress. Furthermore, the decrease in blood thyroxin level is due to the lower body’s heat production that generally indicates an increase in energy retention in the body.