Effects Of The Diet Supplemented With Chromium Yeast On Production Performance Of Laying Hens

The effects of chromium yeast (CrY) added in layer抯 diet on its production performance, egg quality, serum biochemical parmeters and immune function were investigated. 450 layers with the 25weeks old were randomly divided into five groups,among which,one was fed with the basal diet, as the control; other four groups were fed with the different diets added with 0.2, 0.4, 0.6 and 0.8 mg/kg chromium yeast respectively. The experiment lasting 10 weeks was carried out from July to September 2000 in Hefei Shushan Breeding Poultry Farm.The experimental results were as follows:(1)The laying rates of hens were significantly improved with the different concentrations of CrY supplemented in diets during heat stress phase, at P<0.01. Compared with the control, 6.5%(P<0.01) and 7.2% (P<0.01) of the laying rate in the treaments with the supplementation of 0.2mg/kg and 0.8mg/kg CrY were increased in the trial period respectively,but l.5%(P<0.01) and 1.8%(P<0.01) of egg weight in the treaments of 0.2mg/kg and 0.8mg/kg CrY were lowered in the heat stress phase and the comfort phase respectively. The conversion efficiency of feed for the layers was increased by 5.4%,5.4%,4.6% and 7.3% with the increase of CrY added in four treaments respectively, but there were not the significant differences(P>.05).(2)2.9%(P<0.05) to 5.8%(P<0.O1) of the contents of yolk cholesterol were reduced in all treatments compared with the control. There was an increasing trend of calcium deposition in egg from diet in the treatments of 0.6mg/kg or 0.8mg/kg CrY(3)The contents of protein, inorganic ion, creatine phosphokinase, glucose, insulin and thyroxine (T4) in serum were significantly influenced in heat- 49 -stress phase due to the supplementation of CrY in diet. The levels of potassium, phosphorus, magnesium, creatine phosphokinase in serum in the treatments of 0.6mg/kg and 0.8mg/kg CrY were higher than those of the control in heat stress phase, and also 95.2%(P<0.01) and 105.3%(P<0.01) of the content of thyroxine in serum were increased and61 .6%(P<0.01) and 30.1 %(P>0.05) of the content of insulin were increased. Meanwhile, the contents of glucose were reduced by 21.1 %(P<0.05) and 1 9.9%(P<0.05) in the two treatments mentioned above, respectively. In the treatment of 0.4mg/kg CrY, the content of globulin in serum was markedly increased in heat stress phase while 39. 1%(P<0.05) of the content of cholesterol was decreased in comfort phase, compared with the control. The level of alkaline phosphatase in serum in the treatment of 0.2mg/kg CrY had been increased by 89.8%(P<0.05) by the end of the trial. There were no significant differences in the content of cortisol in serum among all treatments, but there was a trend of improvement for serum antibody titer to new castle disease vaccine by the application of CrY in diet.The study demonstrated that the diet supplemented with CrY could significantly raise the capability of anti-heat stress for layers in poor performance.