Blood parameters and fattening performance comparison of Zel and Dallagh male lambs breeds and their crossbred with Romanov breed in different thermal-humidity conditions

This research was conducted in order to compare the blood parameters and fattening performance of Zel and Dalagh breeds male lambs (three to four months old), and their crossbred with Romanov in different thermal-humidity conditions. Fattening trial was conducted in Gonbad kavous with four treatments and six replicates for 84 days from mid-August to early November. Based on the temperature-humiity index (THI), the lambs were under very severe and severe of heat stress up to 8th weeks of trial, followed by non-stress conditions (THI index of 25.6 and above that, 23.3 up to less than 25.6 and less than 22.2 respectively). In the very severe heat stress condition, the performance of treatments was the same. In the severe heat stress, the performance of Dallagh lambs and their crossbred with Romanov was better than Zel and Zel-Romanov crossbred (P<0.05). In un-stress conditions, performance traits in Zel Romanov crossbred was lower than other treatments (P<0.05). Glucose and cholesterol concentration were lower when the lambs were in heat stress condition than normal time (P<0.05). Unlike, blood urea concentration in heat stress condition was higher than lack of stress time (P<0.05). Concentrations of nonstratified fatty acids (NEFA) in the middle period of experiment, during severe heat stress, were higher than those of very severe and nonstress periods. In whole of fattening trial period, all of the breeds had lower performance than expected, indicating the effects of heat stress on them. Totally, Dalagh breed lams had better fattening performance than Zel and their crossbred with Romanov, especially under very severe heat stress condition.