Study Of Clinical Pathology Of High Zinc Diet Long-term Exposure On Effects Of Weanling Piglets

An experiment was conducted to study the effects of feeding high level zinc diet (from 3000 mg·kg^-1ZnO or 500 mg·kg^-1Zn-Met) on the growth performance,serum antioxidative enzyme activities,serum biochemical indexes,the contents of copper,iron, zinc in sera and tissues,and high level zinc diet-applying security in piglets.Sixty "Duroc×Landrace×Yorkshire" crossbred weanling stress piglets(23 d±1 of age) were randomly divided into 3 groups of 20 piglets each by weight and sex.The piglets in GroupⅠwere fed a basal diet,the piglets in GroupⅡwere fed the diets plus 3000 mg·kg^-1 Zinc(from ZnO),the piglets in GroupⅢwere fed the diets plus 500 mg·kg^-1 Zinc(from Zn-Met).The trial was conducted for 70 d.All piglets were weighed on d 0,21,42,70 postweaned,and feed takes were evaluated.Blood samples of sixty piglets were taken from the anterior vena cava on d 0,21,42,70 postweaned for measuring the levels of serum total protein (TP),albumin(ALB),cholesterol(CHL),urea nitrogen(UN),and the activities of serum alkaline phosphatase(ALP),aspartic acid transferase(AST),alanine amino transferase (ALT),CuZn- superoxide dismutase(CuZn-SOD),GSH-Px,and the contents of copper, iron,zinc in sera and dejectas.At the end of the trial,15 male piglets(5 per group) were bled via the anterior vena cava,heart,liver,lung and kidney were collected for determining the contents of copper,iron and zinc;the tissues of kidney and liver were recollected and stored in 10%formalin solution immediately for preparing tissue sections.The results were as follows:(1) The effect of high zinc diet long-term exposure on growth performance of weanling pigletsCompared with the control group,AW of piglets in GroupⅡandⅢwere significantly improved on d 21 and d 42 postweaned(P＜0.01 or P＜0.05),but there were no significant difference(P＞0.05) among 3 groups of piglets at the end of the trial.Compared with the control Group,ADG of piglets in GroupⅡandⅢwere very significantly improved from d 0 to d 21 postweaned(P＜0.01),and significantly improved from d 21 to d 42 postweaned (P＜0.05),and significantly decreased from d 42 to d 70 postweaned(P＜0.05).In the whole experimental period,there had no significant difference of AW and ADG of piglets between GroupⅡandⅢ.(2) High zinc diet long-term exposure could cause poisoning response of weanling piglets The levels of serum AST and ALT were higher in piglets of GroupⅡandⅢthan that of control group(P＜0.05 or P＜0.01) on d 42,70 postweaned,and there were no significant difference between GroupⅡandⅢ(P＞0.05);the levels of serum ALP were higher in piglets of GroupⅡandⅢthan that of control group(P＜0.01) on d 21,42,70 postweaned; the levels of serum TP and ALB were lower in piglets of GroupⅡandⅢthan that of control group(P＜0.05 or P＜0.01) on d 70 postweaned,and there were no significant difference between GroupⅡandⅢ(P＞0.05).In the whole experimental period,there had no significant difference of serum CHL and UN among 3 groups of piglets(P＞0.05).The results indicated that the levels of serum TP and ALB were significantly decreased and the activities of serum AST and ALT were significantly increased in weanling piglets feeding high level zinc diets;zinc toxic symptoms were performed,and there had some pathological changes in liver and kidney.These showed that high zinc diet long-term exposure could cause poisoning response of weanling piglets(3) High zinc diet long-term exposure could cause the imbalance of trance elements in weanling pigletsThe levels of serum copper were lower in piglets of GroupⅡandⅢthan that of control group(P＜0.01) on d 42 and d 70 postweaned.Compared with d 0,the levels of serum zinc in piglets of GroupⅡandⅢwere significantly improved(P＜0.01) on d 21,42 and 70 postweaned.The levels of serum zinc were higher in piglets of GroupⅡandⅢthan that of control group(P＜0.05 or P＜0.01) postweaned;the levels of serum iron were lower in piglets of GroupⅡandⅢthan that of control group(P＜0.01) on d 42 and d 70 postweaned.The contents of zinc were higher in heart,liver,kidney of piglets in GroupⅡandⅢthan that of control group(P＜0.05 or P＜0.01),and the contents of copper and iron were lower in heart,liver,kidney of piglets in GroupⅡandⅢthan that of control group (P＜0.05 or P＜0.01) on d 70 postweaned.The trial results indicated that high zinc diet long-term exposure could increase the contents of zinc in sera and tissues of piglets, inhabit copper and iron absorbing,and increase the contents of copper,iron,zinc in dejecta, decrease the contents of copper and iron in body.The results showed that high level zinc diets could significantly alleviate weanling stress syndrome,enhance the growth performance of piglets on the early period postweaned.High zinc diet long-term exposure could inhabit copper and iron absorbing in body,influnce the liver and kidney function,and cause poisoning response of piglets.