| Meta-analysis is a statistical technique that summaries the results of several studies that address a set of related research hypotheses. Studies chosen for inclusion in a meta-analysis must be sufficiently similar in a number of characteristics in order to accurately combine their results. Meta-analysis can enlarge the numbers of sample, and get more credible conclusions than general systematic reviews.Biotin, as a water-soluble B-vitamin, is an essential nutrient for both rumen bacteria and the dairy cow. Biotin can be synthesized in the rumen for the requirement by low producing cows. As to the high-yielding cows, a high amount of concentrate was fed to meet the nutrition requirement. With the increasing proportion of dietary concentrate, biotin synthesis by ruminal microorganisms will be reduced. Therefore, it is necessary to add biotin in diet for dairy cattle. However the studies on effect of biotin did not get consistent conclusion. The difference between these results may be caused by the small number of animals used in one study and the specific conditions of the experiment. A thoroughly systematic and quantitative assessment of published findings is necessary to arrive at a comprehensive conclusion.The objective of this study was to introduce the application of meta-analysis in two kinds of experiments:the different dosage study with the effect of DC AD on dairy cattle as an example, and the comparative study with the effect of biotin on dairy cattle as an example, And then the animal experiment was used to evaluate the effect of different additional levels of biotin supplementation on milk production, blood biochemical parameters and quality of the hoof in high-yielding dairy cows. Results obtained are as below:1. Application of Meta-analysis in dose studies:it is indicated that Meta analysis can be used to adjust the study effect between studies, and get the optimal additional levels of feed additives. The database was established from 7 studies published between 1994 and 2010 that included 23 dietary treatments and 261 cows. Milk yield, 4% FCM and feed intake were highest when DCAD was 31.6,38.0 and 31.8 meq/ 100 g of dry matter (DM), respectively. Highest blood pH and maximum HCO3" concentrations were reached when DCAD was 45.0 and 46.3 meq/100 g of DM. Milk fat percent increased with the increasing value of DCAD. It is indicated that the DCAD affect the voluntary intake and milk performance, and improve the buffering ability of acid-base balance in the cows.2. Application of Meta-analysis in comparative studies. It is indicated that Meta analysis can be used to get an comprehensive conclusion by combination of servel studies. A total of 11 studies from 9 papers, with information on the milk production and composition data from a total number of 238 cows were extracted and analyzed using meta-analysis software in Stata. Over all the trials analyzed, after the supplementation of biotin, DMI (P= 0.012, n= 178), milk yield (P= 0.002, n= 238), fat yield (P= 0.041, n= 222), and protein yield (P= 0.001, n= 222) increased by 0.87, 1.66,0.05, and 0.05 kg/d, respectively, while there was little effect on the percentage of milk fat (P= 0.531, n= 238) or milk protein (P= 0.546, n= 238). The I2 statistic indicated that heterogeneity for all the variables was not significant (the highest I2= 12%, P= 0.328; the lowest I2= 0, P= 0.575). The result of the Begg's test for publication bias was not significant for all of the variables. Sensitivity analysis revealed that there were no influential studies. The removal of any single study did not change the direction of effect in any analysis, and had little or no change in the overall effect size estimates. It can be concluded that the use of biotin supplements increases dry matter intake and milk yield in lactating dairy cows.3. Effect of biotin on milk performance and hoof quality The objective of this part was to determine the effects of supplemental biotin (0,20,40 mg/d) on lactation performance and hoof quality in dairy cows (n= 45). Treatments started at 40 d and lasted to 110 days in milk. Milk samples were measured weekly; blood samples were taken from coccygeal vein biweekly. Dry matter intake during lactation was not different across treatments (21.4 kg/d). Milk production increased with biotin supplementation (32.7,35.3, and 35.3 kg/d for 0,20, and 40 mg/d of supplemental biotin, respectively). Milk fat percentage and yield, lactose, total solid in milk and concentration of glucose, triglyceride, NEFA in plasma were not affected by biotin supplementation. Similar to 20 mg/d group, protein concentration and yield, and concentration of urea nitrogen in milk and biotin in plasma of 40 mg/d group, were higher than control group. Biotin supplementation did not have effect on moisture content and hardness of hoof in a short period, but made hoof more compact than control group. Supplemental biotin increased milk and protein yields, however, there was no significant difference in milk performance and hoof quality between supplemental levels of 20 and 40 mg biotin per day. Supplemental biotin has no effect on vitro rumen fermentation parameters. The mechanism of biotin on dairy cattle needs further investigations.In summary, Meta-analysis can be used in the research of animal science, including the dose studies and comparative studies, to get more comprehensive conclusions. In this study, the result of meta-analysis shows that biotin improved the milk performance. The experiment shows that additional level 20mg/d is the best for dairy cattle and biotin can reduce microcrack in the hoof of dairy cows. |
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