| Postmilking teat dip is an important tool used to prevent mastitis in the modern dairy industry.The purpose of this study is to prepare a noval barrier teat dip,and estimate its role in the prevention of bovine mastitis.1.Antibacterial activity of chitosan against mastitis-causing bacteria.Minimal inhibitory concentration and inhibition zone tests were used to evaluate the relationship between chitosan molecular weight and antibacterial activity against six mastitis-causing bacteria(Escherichia coli,Pseudomonas aeruginosa,Staphylococcus aureus,Streptococcus agalactiae,Klebsiella pneumonia and Bacillus cereus).It showed that 50 kDa chitosan had maximum antibacterial activity against mastitis-causing bacteria compared with 5,150 and 350 kDa chitosans.So the 50 kDa chitosan was used for the teat dip preparation.2.The preparation of a noval barrier teat dip and its antibacterial activity.Chitosan and povidone-iodine were used as antimicrobial agents in the teat dip.Single factor test was used to determine the optimum ingredient:polyvinyl alcohol-124 6%(w/w),glycerol 4%(w/w),tween 80 1%(w/w),sodium carboxymethyl cellulose 0.45%(w/w),chitosan 1%(w/w),and povidone-iodine 6%(w/w).This teat dip showed good film-forming property and antibacterial activity against mastitis-causing bacteria.The bactericdal power of this teat dip was compared with iodophor on the surface of the dairy cow nipple.After 120 min of application,the bactericdal power of iodophor was disappeared,but the teat dip still remain 48.41%bactericdal power,so this indicated that this teat dip can offer a durable bactericdal power on the surface of the nipple.3.The clinical efficacy of the barrier teat dip(split-herd trial and split-udder trial).A 28 d split-udder trial was conducted using 48 lactating Chinese Holstein cows.Both left teats were immersed in barrier postmilking dip,and both right teats were dipped with nonbarrier postmilking dip(10%povidone-iodine).Beijing mastitis test showed that subclinical mastitis infection rate in the left and right teats were 8.33%and 6.25%at the beginning of the trial,but increased to 9.38%and 14.58%respectively at the end of the trail.No differences in somatic cell count(SCC),somatic cell score(SCS)and other milk quality indicators were observed between left and right teats throughout the trial(P>0.05).In both left and right teats,the SCC and SCS at the beginning of the trail were higher than that at 14 d and 28 d(P<0.05),which indicated that there was a significant decrease in the SCC and SCS in the cows during the trail.During a 28 d split-herd trial,a total of 139 lactating Chinese Holstein cows were classified into a nonbarrier post-milking dip(control group;n=67 cows)and barrier post-milking dip(test group;n=72 cows).During the trail,the subclinical mastitis infection rate in the control group increased from 13.06%to 16.04%,but it decreased from 13.54%to 9.38%in the test group.The X2 test showed that there was a significant difference in the subclinical mastitis infection rate at 28 d between the two groups(X2=5.60,P<0.05).No differences in milk yield,fat content,and protein content were observed between the two groups,but there was a tendency(0.1>P>0.05)for lower SCS and fat-to-protein ratio in the test group compared with control group.In the test group,the SCS at the beginning of the trail was higher than that at 14 d and 28 d(P<0.05),while no difference in SCS was observed in the control group.Overall,the results showed that barrier teat dip containing chitosan and povidone-iodine was effective in preventing subclinical mastitis,and has no effect on the milk quality.Thus,this study not only provides ideas for the development of a new teat dip for the prevention and treatment of cow mastitis,but also has important significance for the promotion of healthy dairy cattle breeding. |
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