Study On The Toxicity Of Dietary Nitrites In Meat-type Ducks

The study is a part of Tolerance level and Method for determination of nitrites in Feeds, supported by the Agricultural National Standard Project of the Ministry of Agriculture. The experiments were conducted to determine the median lethal dose(LD50) of nitrites to ducks, and seek the no-observed effect level(NOEL) in duck feeds.Acute toxicity test. Forty-eight Cherry Valley(C.V) ducks were randomly allotted eight groups, 8 ducks each group. Sodium nitrite was orally administered to these groups through 117.20, 140.66, 168.79, 202.55, 243.05, 291.67, 350, 420 mg/kg body weight respectively. When the dose went beyond 202.55 mg/kg, that group appeared 100% dead. The poisoned animal showed obvious hypoxia or anoxia and metheglobinemia, slight local irritation of gastrointestinal tract. Estimated by Karber's way, the LDso is 159.01 mg/kg body weight, which ninety-five per cent confidence interval is 143.89-175.72 mg/kg body weight.Toxicity feeding trials. One hundred and fifty-six healthy female C.V.ducklings were chosen after being acclimated one week. They were randomized equally on a stratified body weight basis into six groups with a control (0) and five trial groups (1, 2, 3, 4 ,5), each group with two pens. The test was designed six treatment. The six formulated diet contained sodium nitrite (NaNO2) 0, 300, 600, 900, 1200, 1500 mg/kg respectively. It was including earlier period (1~3weeks) and later period (4-6weeks). During the trial the clinical manifestations were observed whenever, weighed one by one and recording feed consumption weekly. At the end of the feeding, drew randomly five ducks out of every group, stripping jugular vein, blood samples were collected in heparinized tubes for haematological analysis. Separated serum samples were gathered for biochemical analysis. Also performed a thorough postmortem examination, describing visible pathological changes, and conducted histopathological studies through paraffin sections. The resultsshowed as follows:The average daily gain(ADG) and average daily feed intake(ADFI) in groups 3, 4, 5 were significantly(P<0.05) or extremely significantly(.P<0.01) lower than control. Others had the same dropping trends, but not significantly. For whole period, the later period was obvious. Feed conversion ratio barely showed any difference(P>0.05). The nigh dose ones, especially groups 4 or 5, had a bad growth, and the mortality rate was beyond 15%.Compared with control, the relative weights of thyroids, hearts, livers and kidneys in groups 3, 4, 5 were significantly higher(P<0.05), those of the spleens and lungs weren't different(P<0.05). Detailed microscopic examination revealed minute changes of some internal organs. Thyroid glands showed mild hyperplasia and proliferation of epithelial lining cells. Section of hearts showed myocarditis with infiltration of mononuclear cells in the myocardium. The lungs occurred alveolar emphysema. The glomeruli presented myxodema. hi the lower dose groups, the incidence and severity were similar to those found in the control.The content of Fib, PCV or RBC was decreasing with MHb concentration increasing. It seemed more clearly later period (P<0.01). Perhaps animals were anemia. TP and GLOB only in group 5 showed statistically noticeable difference(P<0.05). SGPT and SGOT of group 3, 5 were higher than control(P<0.05), as well as CHE of group 4 and CPK of group 5. There was above significant difference on LDH of group 4 or 5(P<0.05 or P<0.05). However, AKP in group 4 and 5 was obviously lower than control(/*<0.05). BUN and UA of group 3,4, 5 showed significantly increased (P<0.05).It could be suggested that the nitrites exceeding 900 mg/kg in feeds caused poor performance and ill-effect on health to ducks. The NOEL of nitrite in formula feed for ducks may be 600~900mg/kg according to this experiment.