| Chromium(?) was administered orally to Hailan layers along with the feed at dosages of 5mg/kg, lOmg/kg and 500mg/kg feed in the form of Chromium Chloride (CrCl3?H2O) during the inoculating period for investigating the effects of the element on Newcastle disease (ND) antibody production. Blood samples were collected at 21, 28,35,42,49,56,63,70d, and the ND antibody titers were determined by hemagglutination inhibition (?I) test. The results indicated that ND antibody titers were significantly higher by using Chromium (?I) at low (5mg/kg feed ) and middle (10Omg/kg feed) dose compared with the control (P<0.01), whereas ND antibody titers were significantly decreased in layers that received Chromium (?) at a high dosage of 500mg/kg feed (P <0.01),though the ND antibody titers of the early days were higher than coutrol's in a short time (P<0.01).A total of 120 2-week old Hailan layers were randomly divided into 4 groups(n=30), and fed a basal diet (control) and the basal diets supplemented with l0mg/kg, 600mg/kg and 1200mg/kg feed Chromium Chloride for 21 weeks, respectively. Then, the layers of the coutrol group and treatment groups were artificially inseminated at the end of 126d (18th week) and 133d (19th week) for observing the egg production performance, fertility and hatchability. The results indicated that the numbers of eggs layed in treatment groups were significantly higher compared with the control's (P<0.05). The fertility, egg shell thickness and egg shell strength treated by a high dosage of 600mg/kg and 1200mg/kg feed chromium chloride were significantly increased, compared with the control (P< 0.05 or P<0.01), but the hatchability was significantly lower (P<0.05 or P<0.01).A total of 50 12-week old Hailan layers were used for investigating acute toxicity of Chromium chloride by using Karber method. The results showed that the median lethal dose (LD50) of chromium chloride to the Hailan chicks was 5013.03mg/kg b.w. after oral administration. The mean confidence limits of LD50 at the probability of 0.95 was5013.03+800.26 mg/kg.b.w.. The results of this histological study indicated the liver of chicks fed on 1200 mg chromium chloride /kg feed group for 21 weeks presents toxic effects with slight fibrosis and inflammation responses.The pharmacokinetics and bioavailability of chromium chloride were studied in healthy adult Hailan chickens after intravenous and oral administration. Chromium chloride was given to 8 chickens at a dosage of 5mg/kg b.w. intravenously, and another 24 chickens were randomly divided into 3 groups (n=8), the chickens of every groups were administered the drug at dosages of l0mg/kg b.w., l00mg/kg b.w. and 250 mg/kg b.w. orally respectively. Plasma chromium (Ⅲ) concentrations were determined by colormetic analysis, with a limit of detection of 0.025 μ g/ml(g). The plasma chromium (Ⅲ) concentration versus time data were fitted to a two-compartment model after a single intravenous injection in chickens. The main pharmacokinetic parameters were as follows: distribution half-life (t1/2α) 0.34±0.03h, elimiation half-life (t(1/2β)) 6.98±0.32h, apparent distribution volume (Vd) 1.93+0.48 L/kg, the area under curve (AUC) 18.33±3.93μThe plasma chromium (Ⅲ) concentrations versus time data following oral adlministration of chromium chloride were analysed by statistical moment method. The results indicated that the areas under curve (AUC) were 1.29±0.37, 3.64±1.27 and 5.28±1.12 μ g/(ml·h), the mean residue time (MRT) 6.80, 7.39 and 6.64 h, and bioavailability (F) 3.52%, 1.04% and 0.58%, respectively, after oral administration at dosages of l0mg/kg b.w., l00mg/kg b.w. and 250mg/kg b.w. of the drug.Thirty chickens were fed a basal diets supplemented with 10mgCrCl3/kg feed for 21 weeks for investigating the residue of chromium (Ⅲ) in tissues. The results showed that chromium could be accumulated in plasma, liver, kidney, muscle, yolk and fat in chickens. The Chromium (Ⅲ) level of plasma and yolk could return to normal (0.12±0.03) u g/ml and (0.20±0.04) μ g/g in 14d a...
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