Effects Of Yeast Culture On Performance And Its Mechanism In Brioler Chicks

The study was conducted to evaluate the effect of supplemental yeast culture in brioler diets on performance,carcass characters,nutrient digestibility,blood physiochemical index,intestinal microorganisms and immunomodulatory functions.Ond-d-old AA chicks(n=960)were randmly assigned to 4 treatments based on corn and soybean meal and containing 0,2.5,5.0 and 7.5g/kg of YC in the diet for 42 d.Each treatment consisted of 12 replicates of 20 broilers.Experiment one:At the 21 and 42-old day,record feed intake and average daily gain, calculate the ratio of diet to meat.Nutrient digestibility was determined on d 15 and 35 by total fecal collection.On d 42,randomly taking one broiler out from each repeat to evaluate carcass characters,and separated left breast and drumstick muscle from body to analyze the protein contents.The results show that(1)on d 21,it has no significantly effect on the daily gain and the average daily gain,and reduce the day feed intake and the ratio of diet to meat of broilers in diets supplied the different levels of YC significantly(P＜0.05).At the 42-old day,It could very significantly improved the average daily gains,reduce the day feed intake and the ratio of diet to meat of broilers by supplied 2.5g/kgYC(P＜0.05).From the whole it could remarkably improve the daily gain and the average daily gain of broilers by supplied 2.5 and 5.0g/kgYC.(2)No differences were found in percentage of breast muscle,the percentage of abdominal fat,percentage of eviscerated carcass and percentage of partly eviscerated carcass among the 4 treatments(P＞0.05).Chicks fed 2.5g/kg and 7.5g/kg yeast culture had increased percentage of drumstick muscle(P＜0.05),no differences were found in protein content of breast and drumstick muscle(P＞0.05).(3)YC supplementation increased digestibility of Ca and P(P＜0.05),but did not affect(P＞0.05)on apparent digestibility rate of CP,GE and DM. When the level of YC is 2.5g/kg,the nutrients in diet have the most utilization.Experiment two:The experiment was conducted to study the effect of the different supplement level of YC on development of immune organ,.At d21and 42,randomly taking one broiler out from each repeat were killed and removed the immune organs(Spleen, Thymus,Bursa.F.)to test weights and calculate the immune organs index;At d14,21,28,35 and 42 after nose instillation immune with Lasota vaccine on d7 and d28,one broiler per group were collected blood from wing's vein,and then separated serum to test Newcastle disease antibody titer and serum biochemical parameter.We examines the Lymphocyte Subsets in the peripheral blood and spleen with Flow Cytometry(FCM).The results showed that:(1)The immune organs index of Thymus,Bursa.F.of 21 and 42-day broilers have significant difference by supplied the different levels of YC,As promoting YC level,the index of immune organs were improved;no differences were found in spleen index.(2)YC improved significantly the antibody titer to New castle disease(NDV)of broilers(P＜0.05).(3) supplying YC improved serum Ca of 21 and 28-day briolers and serum P of 21,35 and 42-day broilers(P＜0.05)..Supplying YC had significant difference in serum T-SOD and SUN (P＜0.05)at 21^th;no difference was found in T-SOD but significantly decreased the content of serum SUN at 35^th;but induced the content of serum T-SOD and SUN at 42^th,but the 3 treatments were not significant difference(P＞0.05).(4)The proportion of CD4⁺ or CD8⁺,the ratio of D4⁺ / CD8⁺ and CD4⁺ / CD3 ⁺in lymphocytes subsets of peripheral blood had a tendency to increase on the 21^thday after supplementation with YC which indicated that body's immunity was enhanced,but has no significant effect on the TCR and the ratio of CD8⁺ / CD3⁺(P＞0.05):YC supplementation decreased CD4⁺ and TCR in lymphocytes subsets of peripheral blood and CD4⁺ lymphocytes and the ratio of CD4⁺ /CD3⁺in spleen lymphocytes subsets(P＜0.05)at 42-old-day which meaned that body's immunity was gradually dropped,but no differences were found in other indicators.Experiment three:this experiment aimed to study the different supplement level of YC on the intestinal microorganisms and multiformity in male broiler chick,At 21 and 42-old day,drew one broiler out per repeat to kill and got the duodenum,jejunum and ileum to test structure by using inverted microscope.We analyze the intestinal microorganisms and multiformity by using Microbial culture counting method and DGGE gel electrophoresis.The results showed that:(1)2.5g/kgYC significantly increased the Villus height and obviously reduced the crypt depth in duodenum,jejunum and ileum on d 21:With the exception of increasing the villus height of duodenum,YC supplementation reduced the villus height of jejunum and ileum compared to control at 42-old-day.(2)YC increase the number of Lactobacillus and Bifidobacterium in ileum and cecum and have no significant effect on the number of E. coil(P＞0.05),Chicks fed 2.5g/kg YC had the best efficiency(P＜0.05),while DGGE Also proved that YC had increased the multiformity of intestinal microorganisms in male broiler chicken.