The Investigation Of IGF-â…  Levels In Milk And Its Prokaryotic Expression And Activity Analysis

Though our country is one of the biggest countries of dairy cow breeding, theoriginal milk does not always have good quality due to the poor productionenvironments and the grim rearing conditions of China’s dairy cows. There is a biggap between China’s current milk quality and foreign countries’. The milk fatpercentage and milk protein rates are two important indicators for the milk quality, theraw milk protein content of China’s milk is on average of2.8g/100g, whereas that ofthe developed countries’ is3.0g/100g. Low quality is one of the main reasons for thedairy adulterated milk. Only if we improve milk protein content in raw milkscientifically, dairy safety will be guaranteed. Studies have shown that the peripheralblood IGF-Ⅰ (PBMC) content of dairy cow with higher milk protein levels wassignificantly higher than that in the control group. There is a correlation between themilk protein content and the milk IGF-Ⅰ content. However, the levels of IGF secretionis closely related to the forage. and the pertinence between milk IGF-Ⅰ and the milkprotein content in Chinese production practices is still unclear. In addition, whetherthe genetically engineered IGF-Ⅰ can promote the growth and development of themammary epithelial cells and lactation, or can be used to improve the milk proteincontent of cows with insufficient IGF-Ⅰ secretion need to be further explored andimprove, are the important foundation of artificial milk quality regulation.This study was carried out in Southern intensive dairy farming where360milksamples were randomly collected to detect milk protein. Milk samples with proteincontent above3.0g/100g were divided into one group and protein content below2.8g/100g were divided into another group. IGF-Ⅰ content were detected by ELISA(enzyme-linked immunosorbent assay) and the correlation between it and the rate ofmilk protein was analyzed. By using one-way ANOVA and multiple regressionanalysis, days of milk lactation, parity, daily milk yield and somatic cell number ofother factors on the rate of milk protein were studied. The results showed that: IGF-Ⅰlevels of high protein milk were significantly higher than the low protein milk. Day ofmilk lactation, daily milk yield, somatic cell count and milk protein rate were correlated. Among them, the milk protein rate showed significant positive correlationwith milk somatic cell number and days of milk lactation, however it showed a highlysignificant negative correlation with daily milk yield. The correlation between parityand the milk protein rate was not significant. The pET-28a-IGF-Ⅰ expression vectorwas constructed using prokaryotic expression system, and induce to express bovineIGF-Ⅰ.We purify the protein by using Ni-Agarose His tag protein purification kit, andto detect its biological activity. The results suggested that: pET-28a-IGF-Ⅰ expressionvector was successfully constructed. Fusion protein IGF-Ⅰ concentration of10ng/ml,100ng/ml and200ng/ml can all promote mammary epithelial cell proliferation andbiosynthesis.The conclusions of this study are: IGF-Ⅰ is the key cytokines that affects milkprotein rate significantly; days of lactation, daily milk yield, somatic cell count are themain factors affecting milk protein rate; fusion protein IGF-Ⅰ expressed in prokaryoticcan promote mammary epithelial cell proliferation and biosynthesis, providing newdrugs to improve the milk protein content of cows with insufficient IGF-Ⅰ secretionand new methods and new ways to artificial milk quality regulation. On thesustainable development of dairy industry, it has important practical significance.