Effect Of Different Zinc Sources And Levels On The Performance And Zinc Utilization In The Tissues Of Broilers

The objectives of this study were to compare the bioavailability of Zn-methionine（Zn-Met）or Zn-Glycine complex（Zn-Gly）relative to Zn sulfate（Zn SO₄）for the broilers from 1 to 14 days of age,and to evaluate an appropriate added Zn level from Zn-Met for 4to 6 week-old broilers fed with a corn-soybean-rapeseed meal diet.Trail 1.The bioavailabilities of Zn-Met and Zn-Gly for the broilers from 1 to 14days of age relative to Zn sulfateA total of 1-day-old 1200 male broilers（Cobb 500）were randomly allotted to 1 of 10treatments with 8 replicate cages（15 birds each cage）in a completely randomized design,involving a 3×3 factorial arrangement of treatments（3 Zn source and 3 Zn level）plus a control with no added Zn.The broilers were fed with the basal diet（containing 26.46 mg of Zn/kg by analysis）or the basal diet supplemented with 40,80 and 120 mg of Zn/kg from Zn-Met,Zn-Gly and Zn SO₄ for 14 days.Compared with the control,Zn supplementation decreased（P<0.05）the average food intake（AFI）and feed intake:body weight gain ratio（F:G）during day 1-7,and increased（P<0.05）the zinc concentration in the liver,pancreas and tibia,and the MT（Metallothionein）concentration and MT m RNA abundance（P<0.05）in the pancreas of broilers on day 7 and 14.The orders of body weight（BW）of 7 day-old broilers and body weight gain（BWG）during day 1-7 were as following:Zn-Gly>Zn-Met>Zn SO₄.During day 8-14 and day 1-14,Zn-Gly and Zn-Met supplementation increased（P<0.05）AFI and BWG compared to Zn SO₄ group.On day 7,the Zn-Met addition increased（P<0.05）tibia Zn concentration compared to Zn-Gly and Zn SO₄,and Zn-Gly and Zn-Met increased（P<0.05）pancreas metallothionein（MT）concentration compared to Zn SO₄.On day 14,the Zn-Met addition increased（P<0.05）pancreas MT m RNA abundance compared to Zn SO₄,whereas there was no significant difference between Zn-Gly and Zn SO₄,or Zn-Met and Zn-Gly groups.The Zn concentration in the tibia and pancreas,as well as the MT concentration and MT m RNA abundance in the pancreas linearly increased（P<0.001）with daily Zn intake increasing on day 7 and 14.According the slope ratio of polynominal regression equation,the bioavailability of Zn-Met and Zn-Gly were 148%and121%relative to Zn SO₄（100%）respectively,evaluated by the MT concentration and MT m RNA abundance in the pancreas of broilers at 7 and 14 days of age.The results suggested that the bioavailability of Zn-Met was higher than that of Zn SO₄,with Zn-Gly in the intermediate.Trail 2.The appropriate added Zn level from Zn-Met for the broilers at 4 to 6weeks of age fed with the corn-soybean-rapeseed meal diet.A total of 22-day-old 1260 male broilers（Cobb 500）were allotted by BW to 1 of 7treatments with 4 replicate cages（45 birds each cage）in a completely randomized design,involving a 2×3 factorial arrangement of treatments（2 Zn source and 3 Zn level）plus a control with the basal diet added 120 mg Zn/kg from Zn sulfate.The broilers were fed the control diet（CON）,or the basal diet（about 62 mg Zn/kg）added with 30,60 and 90 mg of Zn/kg from Zn-Met and Zn SO₄ for 21 days.The reduction of dietary added Zn level did not influence the performance of broilers compared to the CON,except for the decreased AFI by added Zn-Met.Addition of 30,60 and 90 mg/kg Zn from Zn SO₄ decreased tibia Zn level and pancreas MT concentration on day 21,whereas supplemental Zn-Met did not influence tibia Zn,and only addition of 30 mg/kg Zn from Zn-Met reduced pancreas MT compared to the CON（added 120 mg Zn/kg from Zn SO₄）.Addition of 30 and 60 mg Zn/kg decreased pancreas MT m RNA abundance,and supplementation of 30 mg Zn/kg decreased pancreas zinc transporter 2（Zn T2）m RNA abundance compared to the CON（added 120 mg Zn/kg from Zn SO₄）,regardless of Zn source.Compared to Zn SO₄,the Zn-Met increased（P<0.05）tibia zinc concentration and had a trend to increase（P<0.1）serum zinc concentration.The Zn source did not affect（P>0.10）the m RNA abundance of MT and Zn T2 in the pancreas,whereas pancreas MT m RNA expression was higher（P<0.05）in the 90 mg Zn/kg addition treatment than in the 30 and 60 mg Zn/kg addition treatments,and pancreas Zn T2 m RNA abundance was higher（P<0.05）in the 60 and 90mg Zn/kg supplementation groups than in the 30 mg Zn/kg supplementation group.The results suggested the addition of 60 mg Zn/kg from Zn-Met was appropriate level for the broilers from 4 to 6 weeks of age fed with the corn-soybean-rapeseed meal diet.In conclusion,the relative bioavailability of Zn-Met was higher than that of Zn sulfate（147%vs 100%）for the broilers from 1 to 14 days of age.The appropriate added Zn level was 60 mg Zn/kg for the broilers from 4 to 6 weeks of age fed a corn-soybean-rapeseed meal diet.