| This thesis mainly concluded two parts: pre-experiment was conducted to find out whether zincfrom inorganic source had effects on eggshell quality, then studied the effects of different supplementallevel of zinc from inorganic and organic source on performance, egg quality, eggshell quality andantioxidant ability of old laying hens, and tried to find out the influence mechanism to improve eggshellquality.Experiment1. Effects of zinc supplemental level on performance and eggshell quality of oldlaying hensThe experiment was conducted to study the effects of zinc supplemental levels on performance,and eggshell quality of old laying hens. Two hundred and eighty-eight Hy-line laying hens aged52weeks were randomly divided into4groups with6replicates per group and12hens per replicate.During the first7weeks (pre-feeding period), all hens were fed a corn-soybean basal diets containing24.10mg/kg zinc. Experimental diets were introduced at the end of week7and were fed for a total of4weeks, and these diets consisted of the basal diet supplemented with0,35,75,115mg/kg zinc. Theresults showed as follows:1) the supplementation of zinc did not significantly affect the egg productionrate, average daily feed intake, average egg weight and the ratio of feed and egg (P>0.05);2) thesupplementation of zinc significantly increased the eggshell weight (P <0.05), eggshell index (P <0.01), eggshell thickness (P <0.01) and eggshell percentage (P <0.05), and the effects of75and115mg/kg groups were better;3) the supplementation of zinc increased carbonic anhydrase activity both inblood and egg gland (P <0.01), and crystal microstructure of eggshell was improved, the bondingamong crystals were more tightened, the size of crystals was more even and almost all the crystalsshowed vertical growth to the cuticle. In conclusion, the supplementation of zinc in the diet for oldlaying hens does not significantly affect their performance, but trends to increase the eggshell quality byimproving carbonic anhydrase activity of blood and eggshell gland, and crystal microstructure ofeggshell. The optimal level of zinc is75to115mg/kg in the present study.Experiment2. Different supplemental level of zinc from inorganic and organic sources onperformance, egg quality and antioxidant ability in old laying hensThe experiment was conducted to study the effects of different levels and sources of zinc onperformance, egg quality and antioxidant ability of old laying hens. Five hundred and four54-wk-oldHy-line laying were fed a basal diet with Zn level at29.07mg/kg for4weeks and then randomlyallocated into one of the seven dietary treatments: one basal diet (as control) and Zn treatmentssupplemented with35,70,140mg/kg of zinc from either inorganic or organic sources. The resultsshowed as follows:1) the supplementation of zinc from inorganic and organic sources did notsignificantly affect the egg production rate, average daily feed intake and the ratio of feed and egg (P>0.05), the average egg weight of70mg/kg group were significantly decreased in the experiment (P <0.05);2) the supplementation of zinc from inorganic and organic sources had no effects on egg index and egg yolk color (P>0.05); the album height and Haugh unit at61weeks and65weeks old layinghens were significantly affected by sources(P <0.05), eggs from inorganic source were better than eggsfrom organic source; and according to the one-way data, the best egg quality was the group suppliedwith70mg/kg from inorganic source;3) the activity of total superoxide dismutase(T-SOD), Cu/Zn-superoxide dismutase (Cu,Zn-SOD),total antioxidant capacity(T-AOC) and the ability of inhibitingsuperoxide anion both in serum and liver were significantly increased by different levels and sources ofzinc(P <0.01), the content of MDA in serum was significantly decreased after feeding for4weeks (P <0.05), and the best group was70mg/kg from inorganic source or35mg/kg from organic source. Inconclusion, different supplemental levels of zinc from inorganic and organic sources does notsignificantly affect their performance, can improve egg quality and antioxidant capacity in some content.The best level of zinc is70mg/kg from inorganic source in the present study.Experiment3. Different supplemental level of zinc from inorganic and organic sources oneggshell quality and the influence mechanism in eggshell formation of old laying hensThe experiment was conducted to study the effects of different levels and sources of zinc oneggshell quality and the influence mechanism in old laying hens. Five hundred and four54-wk-oldHy-line laying were fed a basal diet with Zn level at29.07mg/kg for4wks and then randomly allocatedinto one of the seven dietary treatments: one basal diet (as control) and Zn treatments supplementedwith35,70,140mg/kg of zinc from either inorganic or organic sources. The results showed as follows:1) the supplementation of zinc from inorganic and organic sources significantly improved the eggshellthickness (P <0.05) and the thickest group was the140mg/kg group from organic source; eggshellstrength, eggshell weight, eggshell index and percentage eggshell were significantly affected by bothsupplementation levels and sources, the best group was70mg/kg from inorganic source according tothe single-factor analysis of variance and the stability between the eggs after feeding for4weeks and8weeks.2) the supplementation of zinc from inorganic and organic sources significantly improved thecapacity of carbonic anhydrase and alkaline phosphatase both in serum and eggshell gland (P <0.05),and the highest group was70mg/kg from inorganic source;3) the supplementation of zinc frominorganic and organic sources significantly increased the mRNA level of carbonic anhydrase, alkalinephosphatase, osteopontin and OC-116in eggshell gland (P <0.05). In conclusion, differentsupplemental levels from inorganic and organic sources significantly improves eggshell quality throughimproving the carbonic anhydrase capacity both in serum and eggshell gland, and the mRNA levels ofcarbonic anhydrase, osteopontin and OC-116in eggshell gland. The optimal level of zinc is70mg/kgfrom inorganic source in the present study. |
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