عنوان مقاله [English]
نویسندگان [English]چکیده [English]
This study was carried out to determine the effects of different levels of protein and probiotic (Protexin) on performance, and immune response in Ross (308) broiler exposed to heat stress. Five hundred and forty one-day old broilers were employed in a compeletly randomized design (3×3 factorial arrangement) of 3 replicates for each treatment. The diets were formulated according to NRC (1994) recommendation with protein levels (90, 100 and 110% of NRC recommendations) along with probiotic (0, 200 and 400 ppm, containing 2×109 cfu/g of spores). The birds were exposed to heat stress (34±3?C) for 8 hours/day (10:00 to 18:00). The results indicated that, the body weight gain in broilers fed NRC plus %110 NRC protein was significantly higher than that in those fed %90 NRC protein (P<0.05). Feed conversion ratio in chicks fed diets containing 100 and %110 NRC protein were significantly improved in comparison with %90 NRC protein diet, within 0-42 days (P<0.05). The addition of 200 ppm probiotic to diets significantly increased body weight gain compared to control during the 0-42 days of age (P<0.05). The treatment containing %110 NRC protein +200 ppm Probiotic, significantly decreased feed conversion ratio as compared with treatments of %90 NRC+probiotic (0 and 400 ppm) in 0-42 day periods (P<0.05). Feeding of %110 NRC versus %90 NRC, along with a feeding of 200 ppm probiotic as against control (0 ppm probiotic), significantly increaseed total protein concentration in broiler's blood serum at its 42 days of age (P<0.05). Serum cholesterol concentration, was significantly lower in broilers fed 200 and 400 ppm probiotic, in comparison with those receiving no probiotic containing diet (P<0.05). Supplementing diet with 200 and 400 ppm probiotic significantly increased WBC count while decreasing H/L as compared with control group (P<0.05). In total, this research indicated that increase in protien level upto %110 of NRC (1994) in diets along with an addition of 200 ppm probiotic would improved the broilers' performance plus their immune response to heat stress, and which could be employed as a measure for diminishing the effects of heat stress.