Mastitis is an important disease causing health, productivity and welfare problems in dairy cattle. Over the past 40 years, control programs have successfully revolved around prophylactic and therapeutic antibiotic usage. This has led to a substantial decrease in the prevalence of subclinical mastitis and the suggestion that antibiotic prophylaxis should be reduced. This thesis describes a study that compared the efficacy of a non-antibiotic internal teat sealer containing bismuth subnitrate to antibiotic dry cow therapy (DCT). In cows uninfected at drying off, the teat sealer was significantly better than antibiotic DCT at preventing new dry period intra-mammary infections caused by Escherichia coli, all Enterobacteriaceae species and all major pathogens. Animals that received antibiotic DCT suffered numerically more cases of clinical mastitis during the dry period and next lactation. Significantly fewer Corynebacterium bovis intra-mammary infections (III) were cured in the teat sealer group during the dry period. A novel method of speciation based on endonucleaser estriction analysis of the 16S rRNA gene sequence was successfully developed and utilized to differentiate C. bovis for other Corynebacterium species. A novel lipophilic Corynebacterium species, named "C. langfordif', was identified, typed by 16S rRNA gene sequencing and described. Re-analysis of the study database demonstrated for the first time that quarters infected with C. bovis during the dry period were significantly less likely to acquire a major pathogen BE. It appeared that IMI with C. bovis "protected" quarters from infection with mastitis pathogens. In vitro studies on solid and in liquid media demonstrated that metabolic products of C. bovis could inhibit the growth of some mastitis pathogens. The inhibitory factor was partially and almost completely inactivated by heating to 100°C and treatment with Proteinase K respectively. Production of an inhibitory factor (possibly a bacteriocin) is proposed as one explanation for the protective effect demonstrated in vivo
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:288286 |
| Date | January 2002 |
| Creators | Huxley, Jonathan Neil |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1983/a38c6483-aed7-4567-ac66-983ba7353672 |
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