| There are three sources of choline to the body of ruminants, one is from the feedstuffs, animals can ingest choline from the feedstuffs; Second, the rumen microorganisms can synthesis choline; Third, the ruminants can synthesis choline through methylation in the body themselves. For the degradation of microorganisms and the ruminants can synthesize choline themselves, little research had been did and it was generally believed that there was not necessary to supply choline additionally to the diet. But experiments showed that high-yielding dairy cows in early lactation may have nutritional deficiencies of choline, and we observed performance improvement to some degrees after choline supplementation.The three experiments were conducted to study the suitable supplementation of choline to early lactating dairy cows in vitro and vivo.1. Randomized block design was used by this trial. By parity, the expected production date, weight, previous parity, milk yield, etc. on a basic principle of consistency, we selected and randomized 40 Holstein cows which were divided into 4 groups (each 10) to research the effects of production performance and blood parameters of dairy cattle in different added gradients of choline. The four treatments were dietary supplementation of 0, 15, 30 or 45 g /d choline chloride (the content of choline chloride was 0,7.5,15,22.5 g ) each cow. The results indicated that, after adding choline, milk production and milk composition are not significantly affected (P> 0.05); Plasma glucose level of the experimental groups were higher than the control group, but the difference was not significant (P> 0.05); After 30 days, adding 45g/d of choline, the plasma BHBA decreased significantly (P <0.05); For plasma CHOl, adding 45g/d choline group was numerically lower than the other three groups, the difference was significant (P <0.01); For the plasma ALT, adding 45g/d choline group was numerically lower than the control group, the difference was significant (P <0.01); For AST, adding 45g/d choline group was numerically lower than the control group, but the difference was not significant (P> 0.05). This showed, fed choline chloride directly could improve the production performance of dairy cows to a certain extent. Most of the tests indicators were significantly different in the the highest addition of choline 45g/d, it showed that this dosage of choline can not be represented the most appropriate addtional concentration of choline. We should increase the feeding amounts of choline further to determine the appropriate dosage.2. 4 healthy multiparous Holstein cows with similar parity, milk yield, and lactation stage were used in a 4×4 Latin square experiment. The four treatments were dietary supplementation of 0, 30, 60, or 90 g /d rumen protected choline (RPC, the content of choline chloride was 0,7.5,15,22.5 g ) each cow. The experiment was divided into four 15-day periods. The results indicated that milk yield, lactose, and milk protein were not influenced by levels of RPC supplementation (P> 0.05). PRC supplementation elevated milk fat content and the highest content were observed when 30 and 60 g/d RPC were supplemented (P<0.05). PRC supplementation did not change plasma HDL, BHBA, TAA, TG, and CHOl (P> 0.05). There was a trend that plasma LDL was increased by PRC supplementation (P<0.1). PRC supplementation decreased plasma NEFA concentration and dropped to the lowest level at the 60g/d treatment. Results of the present study implied that PRC supplementation to early lactation cows might reduce fatty liver risk and increase milk fat synthesis by promoting liver fat output to peripheral tissues. Therefore, the conclusion from this test is that the most appropriate rumen-protected choline dosage for cows in early lactation is 60g/d, the actual content of choline chloride 15 g /d.3. Use the basis of a regular diet as the substrate fermentation, and the method in vitro, study the effect of different amount of choline on rumen microbial metabolism and reproductive performance and its role in the mechanism. There were five treatments with three replications each treatment in the trial, and the five treatment were substrate plus 0, 10, 20, 30, 40mg choline chloride, in which the substrate was 10g. By the determination of PH, NH3-N, VFA and MCP of the medium in 8h, we did not see a good reaction with different concentrations of choline on the impact of various fermentation parameters, because the choline content of substrate may satisfy the requirment of microorganism already. In addition, the rumen environment was complex and affected by vairous factors, we should design further testing according to diet composition, livestock and many other factors, to derive a more reasonable supplementation.
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