| The purpose of this study was to evaluate the effects of using polymer-coated urea and gelatinized starch urea to replace part of the plant protein in the diet on the growth performance,nutrient digestibility,blood biochemical indicators,ruminal fermentation and microflora in beef heifer.The first experiment was to evaluate the release rate of the two different slow release urea in phosphate buffer in vitro.The results showed that,After 2h digestion,62.43% of the urea was dissolved,and after 8h digestion,95.10% of the urea was dissolved,while the starch gelatinized urea,After 2hours of digestion,93.53% of urea was dissolved,and after 8 hours of digestion,99.93%of urea was dissolved,indicating that polymer-coated urea has a better slow-release performance.The second experiment was a feeding trial.210 purebred Angus heifers that about 13 months old was selected,According to the principle of the same or similar body weight and month age,the three heifers were paired,and each pair of animals was randomly divided into 3 groups,The control group,the polymer-coated urea group and the gelatinized starch urea group,70 heifers in each group.To prepare a basic diet refer to NRC(2016)nutrient requirements of Beef cattle.The polymercoated urea group and the gelatinized starch urea group use 2% polymer-coated urea and 2.5% gelatinized starch urea to replace part of the soybean meal in the concentrate respectively according to the principle of iso-metabolic energetic and iso-nitrogenous.The pre-feeding period is 7 days,and the normal feeding period is 90 days.The results showed that:(1)In the second month,the ADG of the polymer-coated urea group was extremely significantly higher than that of the control group and gelatinized starch urea group(P<0.01);the feed efficiency was significantly lower than that of the control group(P<0.05),and was extremely significantly lower than gelatinized Starch urea group(P<0.01).Throughout the trial period,the average daily gain of the polymer-coated group was significantly higher than that of the gelatinized starch urea group(P<0.05),and was extremely significantly higher than that of the control group(P<0.01);the feed efficiency of the polymer-coated urea group was significantly lower than that of the gelatinized Starch urea group(P<0.05)and control group(P<0.05).(2)The apparent digestibility of EE in the gelatinized starch urea group was significantly higher than that in the control group(P<0.05),the apparent digestibility of ADF in the polymer-coated urea group was significantly higher than that in the control group(P<0.05),and extremely significantly higher than the gelatinized starch urea group(P<0.01);the difference in digestibility of other nutrients was not significant.(3)Among the serum biochemical indexes on day 49,the ALT activity of the gelatinized starch urea group was significantly higher than that of the polymer-coated urea group(P<0.05).In the serum biochemical indexes on day 86,the ALB content of the polymer-coated urea group was significantly higher than that of the control group(P<0.05);the AN concentration,ALT and AST activities of the gelatinized starch urea group were significantly higher than those of the control group(P<0.05).There were no significant differences in other serum biochemical indicators at each sampling time point(P>0.05).(4)In terms of rumen fermentation,the contents of acetic acid and butyric acid(P<0.05),propionic acid and total volatile fatty acids(P<0.01)in the polymer-coated urea group were significantly or extremely significantly higher than those of the control group;the gelatinized starch-urea group propionic acid The content of and butyric acid was significantly higher than that of the control group(P<0.05);the ethylene-topropylene ratio of the control group was significantly higher than that of the polymercoated urea group and the gelatinized starch urea group(P<0.05).(5)In terms of rumen microflora,the metagenomic sequencing method found that the relative abundance of Bacteroidetes in the gelatinized starch urea group was significantly higher than that in the polymer-coated urea group(P<0.05);compared with the control group,the relative abundance of Bacteroidetes was significantly higher than that in the polymer-coated urea group(P<0.05);Firmicutes in the urea group increased by 14.12%(P>0.05),and Firmicutes in the gelatinized starch urea group decreased by 29.16%(P>0.05).The relative abundance of Prevotella in the gelatinized starch urea group was significantly higher than that in the polymer-coated urea group(P<0.05);Ruminococcus in the polymer-coated urea group was compared with the control group and the gelatinized starch urea group,respectively Increased by 3.61%and 32.31%(P>0.05).Compared with the control group and gelatinized starch urea group,Ruminobacter increased by 127.40% and 22.06%(P>0.05).There was no significant difference in the relative abundance of rumen fungal flora in each group.(6)Both types of slow release urea can reduce the cost of weight gain in kilograms and bring certain economic benefits,and the economic benefits of polymer-coated urea are more significant.In summary,both polymer-coated urea and gelatinized starch urea can replace part of the soybean meal in the diet.The replacement amount in this experiment has no adverse effect on the performance of Angus reserve cows.Both types of slow-release urea can bring certain effects.The economic benefit,the use effect and economic benefit brought by polymer-coated urea are better than gelatinized starch urea. |
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