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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Prevention of the neutrophil-induced mammary epithelial damage during bovine mastitis

Lauzon, Karoline. January 2005 (has links)
Reduction of milk production following acute bovine mastitis causes important economic losses. In this study, two experiments were conducted to asses the ability of different antioxidants to prevent neutrophil (PMN)-induced mammary damage in acute bovine mastitis. First, a co-culture model composed of bovine mammary epithelial cell line (MAC-T cells) and bovine PMN activated by phorbol myristate acetate was used. Activated PMN release reactive oxygen species that are cytotoxic for bovine epithelial cells. Addition of dimethylthiourea or bathocuproinic acid did not induce any protective effect. On the other hand, addition of catechin, deferoxamine or glutathione ethyl ester (GEE) significantly reduced PMN-induced cytotoxicity in a dose-dependent manner as demonstrated by lower levels of released lactate dehydrogenase (LDH). The second experiment was undertaken with the last three antioxidants to evaluate their protective effects in vivo. A model of LPS-induced mastitis on dairy cows was used. The extent of cell damages was evaluated by measuring quarter milk levels of LDH and 4-methylumbelliferyl N-acetyl beta-D-glucosaminidase ( NAGase) at varying intervals before and after intramammary infusions of LPS, with or without antioxidants. Milk levels of haptoglobin and bovine serum albumin were also analysed. Catechin and GEE did not induce any protective effect whereas infusions of deferoxamine, a chelator of iron, decreased milk levels of LDH, NAGase and haptoglobin hence suggesting a protective effect against PMN-induced damage. Deferoxamine did not interfere with PMN migration into the mammary gland. Additionally, deferoxamine inhibited bacterial growth in vitro but did not affect PMN's ability to phagocytize live Escherichia coli. Overall, our results suggest that local infusion of deferoxamine may be an effective tool to protect mammary tissue against PMN-induced oxidative stress during bovine mastitis.
2

Effects of human chorionic gonadotropin administration at various times following breeding on corpus luteum number, diameter, progesterone profiles and pregnancy rates in dairy cattle

Sianangama, Pharaoh Collins January 1990 (has links)
Corpus luteum (CL) dysfunction has been implicated among various factors predisposing early embryonic mortality in cattle. Two experiments were conducted to evaluate the efficacy of using human chorionic gonadotropin (hCG) given either at the time of breeding (day 0) , day 7 or 14 post breeding, in reducing that component of early embryonic mortality caused by CL dysfunction. The aims of experiment 1 were to investigate the effectiveness of using hCG, in inducing the development of accessory CL, their formation and growth, and the effect of such treatments on the function of both the induced and spontaneous CL. Thirty-four lactating Holstein cows were randomly assigned to one of four treatments. A single intramuscular injection of 1000 IU of hCG was given either at the time of breeding (day 0, n=8), day 7 (n=9) or 14 (n=9) post breeding or no hCG given (control, n=8). A real-time ultrasound machine was used to study follicular dynamics and CL growth. The CL and antral follicle diameter was determined using a built-in system of calibrated callipers. Ultrasound scanning was carried out on days 7, 9, 11, 14, 16, 18, 21, 28, 35 and 42 post breeding. Blood and milk samples, for progesterone (P₄) determination using radioimmunoassay, were collected on days coincident with ultrasonography. Diameter of the CL is presented as the sum of the diameter of all luteal tissue in each animal. Differences in CL diameter, milk and plasma P₄ were analyzed using the General Linear Models Procedures while pregnancy data were analyzed using Chi-Square analysis in Statistical Analysis Systems (SAS, version 6.3). Based on the day 7 ultrasound scanning, the incidence of twin ovulations was higher among cows treated on day 0 (3/8) compared to control cows (1/8) and day 7 (1/9). Accessory CL were detected in 7/9 of the day 7-treated cows compared to 4/9 among the day-14 treated cows. Least squares means (LSMeans) for CL diameter were significantly higher (P<0.001) among cows treated with hCG compared to control cows starting at day 7 continually until day 42. Plasma P₄ profiles were significantly higher (P<0.05), at days 18, 35 and 42, in cows treated on day 7 or 14 compared to control cows. The first detectable differences (P<0.05) between hCG treated and control cows, in milk P₄ occurred at day 21 and persisted until day 42. Pregnancy rates were highest among cows treated with hCG on day 7 where 6 of the 9 cows were diagnosed pregnant. Corresponding pregnancy rates for day 0, 14 or control cows, were 4/8, 5/9 and 3/8, respectively. In the second experiment, two trials were conducted at two different farms to investigate the efficacy of using hCG to increase milk P₄ and pregnancy rates. In trial one, 79 lactating Holstein cows were exposed to the treatment protocol described in experiment 1. In addition to the milk sample collection schedule given in experiment 1, a sample was collected on day 0. Milk samples were stored at 4°C and later transported to the UBC laboratories for P₄ analysis. LSMeans for milk P₄ concentrations were different only at days 16 and 18 post breeding. Pregnancy rates were improved (P<0.01) by hCG treatments. The respective pregnancy rates for cows receiving hCG on day 0 (n=20), 7 (n=20), 14 (n=20) or control (n=19) were 25, 35, 35 and 21 %. In the second trial, 121 lactating Holstein cows were randomly assigned to treatments as described earlier. Weekly milk samples were collected from each animal and assayed for P₄ as described above. LSMeans for milk P₄ were significantly different (P<0.05) among groups starting at day 14 until day 42 post breeding. hCG increased pregnancy rates over control cows. The pregnancy rates for cows treated on day 0, 7, 14 and control were 31, 50, 41 and 26 %, respectively. In conclusion, this study revealed that treatment with hCG induced accessory CL development, increased P₄ production and improved pregnancy rates. It is evident, too, that treatment with hCG on day 7 post breeding may have greater potential for improving pregnancy rates not only in dairy and beef cattle but equally beneficial to the embryo transfer programmes. Increased pregnancy rates confirm the hypothesis that CL dysfunction does cost the livestock industry appreciable losses in embryos. / Land and Food Systems, Faculty of / Graduate
3

Modelling the transmission of and effectiveness of control measures for Mycobacterium avium subsp. paratuberculosis in dairy herds

Marcé, Clara L. H. January 2010 (has links)
No description available.
4

Biological and molecular characterization of South African bacteriophages infective against Staphylococcus aureus subsp. aureus Rosenbach 1884, casual agent of bovine mastitis.

Basdew, Iona Hershna. 27 November 2013 (has links)
Bacteriophage therapy has been exploited for the control of bacterial diseases in fauna, flora and humans. However, the advent of antibiotic therapy lead to a cessation of most phage research. Recently, the problem of antibiotic resistance has rendered many commonly used antibiotics ineffective, thereby renewing interest in phage therapy as an alternative source of control. This is particularly relevant in the case of bovine mastitis, an inflammatory disease of bovine mammary glands, caused by strains such as Staphylococcus aureus subsp. aureus Rosenbach 1884. Antibiotic resistance (primarily towards penicillin and methicillin) by staphylococcal strains causing mastitis is regularly reported. Phage therapy can provide a stable, effective and affordable system of mastitis control with little to no deleterious effect on the surrounding environment or the affected animal itself. Several studies have delved into the field of biocontrol of bovine mastitis using phages. Results are variable. While some phage-based products have been commercialized for the treatment of S. aureus-associated infections in humans, no products have yet been formulated specifically for the strains responsible for bovine mastitis. If the reliability of phage therapy can be resolved, then phages may become a primary form of control for bovine mastitis and other bacterial diseases. This study investigated the presence of S. aureus and its phages in a dairy environment, as well as the lytic ability of phage isolates against antibiotic-resistant strains of mastitic S. aureus. The primary goals of the thesis were to review the available literature on bovine mastitis and its associated control, and then to link this information to the use of phages as potential control agents for the disease, to conduct in vitro bioassays on the selected phages, to conduct phage sensitivity assays to assess phage activity against different chemical and environmental stresses, to morphologically classify the selected phages using transmission electron microscopy, to characterize the phage proteins using one-dimensional electrophoresis, and lastly, to characterize phage genomes, using both electrophoresis as well as full genome sequencing. Twenty-eight phages were isolated and screened against four strains of S. aureus. Only six phages showed potential for further testing, based on their wide host range, high titres and common growth requirements. Optimal growth conditions for the host S. aureus strain was 37°C for 12hr. This allowed for optimal phage replication. At an optimal titre of between 6.2x10⁷ to 2.9x10⁸ pfu.mlˉ¹(at 10ˉ⁵ dilution of phage stock), these phages were able to reduce live bacterial cell counts by 64-95%. In addition, all six phages showed pathogenicity towards another 18 S. aureus strains that were isolated from different milk-producing regions during a farm survey. These six phages were named Sabp-P1, Sabp-P2, Sabp-P3, Sabp-P4, Sabp-P5 and Sabp-P6. Sensitivity bioassays, towards simulated environmental and formulation stresses were conducted on six identified phages. Phages Sabp-P1, Sabp-P2 and Sabp-P3 showed the most stable replication rates at increasing temperatures (45-70°C), in comparison to phages Sabp-P4, Sabp-P5 and Sabp-P6. The effect of temperature on storage of phages showed that 4ºC was the minimum temperature at which phages could be stored without a significant reduction in their lytic and replication abilities. Furthermore, all phages showed varying levels of sensitivity to chloroform exposure, with Sabp-P5 exhibiting the highest level of reduction in activity (74.23%) in comparison to the other phages. All six phages showed optimal lytic ability at pH 6.0-7.0 and reduced activity at any pH above or below pH 6.0-7.0. Exposure of phages to varying glycerol concentrations (5-100%) produced variable results. All six phages were most stable at a glycerol concentration of 10-15%. Three of the six isolated phages, Sabp-P1, Sabp-P2 and Sabp-P3, performed optimally during the in vitro assays and were used for the remainder of the study. Morphological classification of phages Sabp-P1, Sabp-P2 and Sabp-P3 was carried out using transmission electron microscopy. All three phages appeared structurally similar. Each possessed an icosahedral head separated from a striated, contractile tail region by a constricted neck region. The head capsules ranged in diameter between 90-110nm with the tail length ranging from 150-200nm in the non-contractile state and 100-130nm in the contractile state. Rigid tail fibres were also visible below the striated tail. The major steps in the virus replicative cycle were also documented as electron micrographs. Ultra-thin sections through phage plaques were prepared through a modification of traditional methods to speed up the process, with no negative effects on sample integrity. The major steps that were captured in the phage replicative cycle were (1) attachment to host cells, (2) replication within host cells, and, (3) release from cells. Overall results suggested that all three phages are strains from the order Caudovirales and are part of the Myoviridae family. A wealth of information can be derived about an organism based on analysis of its proteomic data. In the current study, one-dimensional electrophoretic methods, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), and ultra-thin layer isoelectric focusing (UTLIEF), were used to analyse the proteins of three phages, Sabp-P1, Sabp-P2 and Sabp-P3, in order to determine whether these strains differed from each other. SDS-PAGE analysis produced unique protein profiles for each phage, with band fragments ranging in size from 8.86-171.66kDa. Combined similarity matrices showed an 84.62% similarity between Sabp-P1 and Sabp-P2 and a 73.33% similarity between Sabp-P1 and Sabp-P3. Sabp-P2 showed a 69.23% similarity to Sabp-P3. UTLIEF analysis showed protein isoelectric charges in the range of pI 4.21-8.13, for all three phages. The isoelectric profiles for each phage were distinct from each other. A combined similarity matrix of both SDS-PAGE and UTLIEF data showed an 80.00% similarity between phages Sabp-P1 and Sabp-P2, and a 68.29% similarity between Sabp-P1 and Sabp-P3. Sabp-P2 showed a 70.59% similarity to Sabp-P3. Although the current results are based on putative protein fragments analysis, it can be confirmed that phages Sabp-P1, Sabp-P2 and Sabp-P3 are three distinct phages. This was further confirmed through genomic characterization of the three staphylococcal phages, Sabp-P1, Sabp-P2 and Sabp-P3, using restriction fragment length analysis and whole genome sequencing. Results showed that the genomes of phages Sabp-P1, Sabp-P2 and Sabp-P3 were all different from each other. Phages Sabp-P1 and Sabp-P3 showed sequence homology to a particular form of Pseudomonas phages, called "giant" phages. Phage Sabp-P3 showed sequence homology to a Clostridium perfringens phage. Major phage functional proteins (the tail tape measure protein, virion structural proteins, head morphogenesis proteins, and capsid proteins) were identified in all three phages. However, although the level of sequence similarity between the screened phages and those already found on the databases, enabled preliminary classification of the phages into the order Caudovirales, family Myoviridae, the level of homology was not sufficient enough to assign each phage to a particular type species. These results suggest that phage Sabp-P1 might be a new species of phage within the Myoviridae family. One longer-term objective of the study is to carry out complete assembly and annotation of all the contigs for each phage. This will provide definitive conclusions in terms of phage relatedness and classification. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

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