| Copper is an essential trace element for body growth.A large number of studies have shown that high copper can improve the production performance and feed conversion of piglets,which was once widely used in pig production.However,the utilization rate of copper in feed is low,and the environmental pollution caused by high copper addition has aroused great attention.Long-term feeding of high copper diet not only leads to copper accumulation in a breeding environment,but may also leads to oxidative stress,decreased growth performance and tissue copper accumulation in pigs and potential food safety risk.It is currently an important research content to study the response of metabolism,physiology and intestinal microflora of pigs at different stages to dietary copper levels and dosage forms,and scientifically reduce the addition of copper on the premise of ensuring the production efficiency in breeding.Therefore,the effects of different dosages of copper sulfate addition during weaning,growing and finishing stages on copper deposition and nutrient utilization in pigs and pork quality of finishing pigs were studied in this paper,and the alleviating effects of decreasing the level of copper addition on oxidative stress and intestinal flora disturbance in pigs were explored in the meantime.In addition,the feeding effects of substitution of copper glycinate for copper sulfate were studied.The main results of this paper are as follows:(1)In the first experiment,48 weaned piglets at 21 days old were selected and randomly divided into 4 groups.The piglets,respectively,were fed diets supplemented with different levels of copper sulfate(0,20,100 and200 mg Cu/kg feed)and slaughtered for sampling at 3 and 6 weeks after the start of the experiment.Copper deposition in liver,kidney and brain increased with dietary copper levels(P<0.05).At 3 weeks after the start of the experiment,serum MDA level first decreased and then increased,and the activities of GPX,CP and CAT first increased and then decreased with dietary copper levels(P<0.05).High level of dietary copper(200 mg Cu/kg feed)significantly affected the compositions of microbial flora in the ileum and cecum(P<0.05),and significantly increased the ratio of intestinal Escherichia coli resistant to chloramphenicol and ciprofloxacin(P<0.05).Changes in the abundances of microbial flora may be related to metabolic functions such as energy metabolism,protein metabolism,amino acid biosynthesis and metabolism,and so on in piglets.(2)In the second experiment,102 weaned piglets at 21 days old were selected and randomly divided into 6 groups.In the first stage,the piglets,respectively,were fed diets supplemented with different levels of copper sulfate(0,25,50,75,100 and 125 mg Cu/kg feed)until about 25 kg BW.In the second stage,all the experimental pigs were fed with diets containing25 mg Cu/kg feed until about 100 kg BW.Slaughtering and sampling was performed at 3 weeks after the start of the experiment and at the end of the experiment.The results showed that there was no significant difference in growth performance after 3 weeks(P>0.05).Copper levels in liver,kidney,cecal contents and feces increased with dietary copper levels in weaned piglets(P<0.05).Crypt depth of duodenum and jejunum and apparent digestibility of crude protein and energy first increased and then decreased with dietary copper levels in weaned piglets(P<0.05).Crypt depth of duodenum and jejunum and apparent digestibility of crude protein and energy showed a significant quadratic relationship with dietary copper levels(P<0.05).Dietary copper levels positioned at the vertex of quadratic curve were distributed in the range of 19.50 to 63.83 mg/kg.With increase in dietary copper levels,the levels of free Phe,Thr,Met,Val and Leu in dorsal muscle and free Phe,Val,Leu and Ile in biceps femoris muscle decreased(P<0.05),while the relative amounts of UFA and UFA/SFA ratio in dorsal muscle and water holding capacity of the biceps femoris muscle first increased and then decreased during the fattening period(P<0.05).Therefore,it is recommended that the optimal dietary copper levels for weaned piglets(weighing no more than 25 kg)are in the range of 19.50 to63.83 mg/kg.(3)In the third experiment,1200 piglets weighing about 25 kg were selected and randomly divided into 5 groups.The piglets,respectively,were fed diets supplemented with different levels of copper sulfate(0,4,8,16 and 32 mg Cu/kg feed)until about 110 kg BW.With increase in dietary copper levels,copper levels in feces increased(P<0.05),serum ALP activities and the bone percentage in carcass first increased and then decreased(P<0.05),and drip loss of dorsal muscle first decreased and then increased(P<0.05).The blood lymphocyte count in the group supplemented with 8 mg Cu/kg feed was significantly higher than that in other groups(P<0.05).Serum ALP activities and drip loss of dorsal muscle showed a significant quadratic relationship with dietary copper levels(P<0.05).Dietary copper levels positioned at the vertex of quadratic curve were distributed in the range of 15.74-20.00 mg/kg.Therefore,it is recommended that the optimal dietary copper levels for growing finishing pigs(25 to 110 kg)are in the range of 15.74-20.00 mg/kg.(4)In the fourth experiment,68 weaned piglets at 21 days old were selected and randomly divided into four groups.In the first stage,the piglets,respectively,were fed diets supplemented with copper sulfate(0,25,125 mg Cu/kg feed)and copper glycinate(25 mg Cu/kg feed)until about 25 kg BW.In the second stage,all the experimental pigs were fed with diets containing 25 mg Cu/kg feed until about 100 kg BW.Slaughtering and sampling was performed at 3 weeks after the start of the experiment and at the end of the experiment.Compared with the group supplemented with 25 mg Cu/kg feed from copper sulfate,manganese deposition in liver,crypt depth of jejunum,apparent digestibility of crude protein and energy and Shannon index of cecal microflora significantly decreased(P<0.05),serum P level significantly increased(P<0.05),and copper levels in cecal contents and feces showed a decreasing trend in the group supplemented with copper glycinate in weaned piglets(P>0.05).Compared with the group supplemented with 25 mg Cu/kg feed from copper sulfate,the levels of free Lys and Thr in dorsal muscle significantly increased during the fattening period in the group supplemented with copper glycinate(P<0.05).In short,copper glycinate has no obvious advantage in taking the place of application of inorganic copper.It is concluded that high level of dietary copper supplementation is not suitable for application in pig production,the optimal dietary copper levels for weaned piglets and growing-finishing pigs are respectively in the range of 19.50 to 63.83 mg/kg and 15.74-20.00 mg/kg and that copper glycinate has no obvious advantage in taking the place of application of inorganic copper. |
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