الخلاصة

This study was conducted in ruminant Farm at the Department of Animal Production, Faculty of Agriculture, University of Kufa, Najaf, Iraq. Twenty four of Iraqi lambs (4-5 month of age) in a completely randomized design with a factorial arrangement of treatment: 2 breed (Arabi vs. Awassi) ×2 levels of addition of commercial Saccharomyces cerevisiae (SC) (0 vs. 5gSC/head/day) were used to study the effect of breed and level of SC addition on growth performance. All lambs were fed concentrate diet at rate 3% of live body weight and free choice to the roughage mixture (20% alfalfa hay+ 10% rice straw) for 56 days. The results revealed that no significant difference between Arabi and Awassi lambs in final body weight P>0.05).Average daily gain was higher (P<0.01) with Arabi lambs than Awassi. Arabi lambs fed diet with 5 g SC/head/day had higher (P<0.01) total gain and average daily gain than those fed without SC .It can be concluded that the addition of commercial yeast to the diet had positive effect on final body weight of both bred (Awassi and Arabi lambs), and the best increased in total and daily weight gain was achieved with Arabi lambs.