| Two experiments were conducted to investigate the most suitable conditions for yeast to enrich iron and the bioavailability of iron-enriched yeast in weanling piglets.Exp 1 aimed to select the more suitable conditions for preparing iron-adapted yeast by investigating the character of Saccharomyces cerevisia,the initial pH and iron concentration in medium.The results suggested that Saccharomyces cerevisia can adapt 5-7 pH(nature pH) and grow well in 800mg L-1 iron condition for 48h.We chose these iron concentration as the initial concentration of naturalization.In the last,yeast was cultured in natural medium with initial pH 6.0,iron concentration 800mg L-1 for 48h.The yeast output was 12.9g L-1 and contained iron 23.94 mg g-1 with 98.14%of iron being organic.The iron-enriched yeast was then produced under 50L fermenter.The yeast output was 26.5g L-1 and contained iron 25.51mg g-1 with 97.84%of iron being organic.Exp 2 studied on the bioavailabiity of iron-enriched yeast for weanling piglets. Thirty-five 21d weanling DLY piglets with an average weight of(5.57±0.83) kg were randomly allocated into seven dietary treatments with five replicates(one pig per replicate).The basal diet containing 22.43 mg kg-1 iron was the control diet.80,120 and 180mg kg-1 iron either from iron-enriched yeast or ferrous sulfate were added into the semi- purified basal diet.The trial duration was 10 days after 28-day depletion period.The results showed that 1) Hb and SI were decreased by 22.46%and 27.91%respectively, meanwhile the TIBC and ceruloplasmin content were increased by 169.92%and 27.22% after depletion period.So a piglets' model of iron deficiency was successfully established. 2) There was a significant effect on ADG and ADFI of iron-enriched yeast(120mg kg-1 ) (P＜0.05).But there were no significant differences between iron resources and among levels and iron resources×levels for ADG or ADFI.3) There was no effect of CMH on the blood convention(P＞0.05).Iron-enriched yeast supplementation enhanced serum iron, ferroprotein and transferrin significantly(P＜0.01),however decreased total iron binding capacity and ceruloplasmin significantly(P＜0.01).Meanwhile,the effect of iron-enriched yeast was better than the iron sulfate.Both iron-enriched yeast and iron sulfate might increase significantly iron content than control group in the internal organs,including spleen,liver,kidney and the heart(P＜0.01).There were no significant effects on iron content of lung.The iron content of internal organs of ferrous sulfate was significantly higher than that of iron-enriched yeast(P＜0.01).4)According to the slope-ratio technique from regression of common logarithm value of different indicators with dietary iron level, it was found that relative bioavailability of iron-enriched yeast was different.The bioavailability of iron-enriched yeast based on Hb,ceruloplasmin,serum iron,total iron binding capacity was higher than ferrous sulfate with average being 13.56%.The conclusion was that two different iron sources had no effect on the growth performance of piglets,but iron-enriched yeast at levels of 120mg kg-1 had better effects than ferrous sulfate.The conclusion shown that iron-adapted Saccharomyces cerevisia cultured in natural medium with initial pH 6.0,iron concentration 800mg L-1 and temperature 28～30℃for 48h can produce iron-enriched yeast product with copper content 25.51 mg/g and higher utilization efficiency with average bioavailability being 113.56%relative to ferrous sulfate. |
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