Browsing by Author "Kerslake, Joanne Isabel"
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- ItemImproving triplet lamb survival in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Palmerston North, New Zealand(Massey University, 2010) Kerslake, Joanne IsabelThis thesis sets out to identify physical and physiological differences between lambs of different birth ranks at birth, and to use this information to identify practical on-farm management strategies which could improve triplet-born lamb survival. Triplet-born lambs, especially the lightest-triplet-born lambs, not only had a greater capacity to lose heat but also had a reduced capacity to produce heat when compared to twin-born lambs. Due to their lighter birth weights, triplet-born lambs had lower plasma thyroxine (T4) concentrations within the first 24 hours of life than twin-born lambs, and within twin- and triplet-born litters, the lightest- and medium-triplet-born lambs had greater plasma lactate concentrations than all twin-born lambs and the heaviest-triplet-born lambs. Independent of lamb birth weight, triplet-born lambs had lower plasma tri-iodothyronine (T3) concentrations within five minutes of birth, and within twin- and triplet-born litters, the lightest- and medium-triplet-born lambs had lower plasma T4 and T3 concentrations within five minutes of birth than all twin-born lambs and the heaviest-triplet-born lambs. It was hypothesised that because triplet-born lambs had a lighter birth weight and lower plasma thyroid hormone concentrations, they would have inadequate thermoregulatory capabilities when compared to twin-born lambs. The lower rectal temperatures of triplet-born lambs within the first hour of life and the lower heat production on a per lamb basis at 24 to 36 hours of age, and the lack of difference in maximum heat production on a per kg of birth weight basis at 24 to 36 hours of age support this hypothesis. Two practical on-farm management strategies trialled in this thesis to improve triplet-born lamb thermoregulation were offering concentrate supplement during late pregnancy to improve lamb birth weights, and maternal iodine supplementation to improve lamb plasma thyroid hormone concentrations. While offering concentrate showed positive effects such as increasing lamb birth weights, colostrum uptake and triplet-born lamb heat production on a per kg of birth weight basis, the results were either inconsistent across experiments or between birth ranks suggesting additional work is required to determine the repeatability and cost effectiveness of these findings. Maternal iodine supplementation offered no iv | P a g e benefits in terms of lamb birth weights, plasma thyroid hormone concentrations or lamb heat production. Further investigations identified that lamb birth weights, thyroid hormone concentrations, glucose and NEFA concentrations are positively associated with maximum heat production at 24 to 36 hours of age. Practical on-farm management strategies which could target these physical and physiological factors may improve triplet-born lamb heat production, and therefore the survival rates of triplet-born lambs.
- ItemSalmonella Brandenburg in New Zealand sheep : the development of a serological diagnostic test and a case control study : a thesis presented in partial fulfilment of the requirements for the degree of Master of Veterinary Studies at Massey University(Massey University, 2003) Kerslake, Joanne IsabelSalmonella Brandenburg causes acute diarrhoea and severe illness in a variety of animals and was first isolated in New Zealand in 1986. Since 1996 Salmonella Brandenburg has been associated with an emerging epidemic of abortions and deaths in sheep in the southern regions of the South Island. Little is known about the specific epidemiology of Salmonella Brandenburg in sheep and as a result control to date has been largely based on anecdotal evidence and general principles. This study focused on the following aims: • To develop a serological test for use in epidemiological studies and for monitoring future control efforts targeting Salmonella Brandenburg in New Zealand sheep. • To identify factors associated with the occurrence and severity of Salmonella Brandenburg outbreaks in New Zealand sheep. Traditionally Salmonella diagnosis has depended on bacteriological culture. Such tests are time consuming, labour and equipment intensive, and may lack sensitivity. ELISA (Enzyme-Linked Immunosorbent Assay) methodologies offer an alternative for the diagnosis of Salmonella infection. Therefore the development of an ELISA test for detecting antibodies to Salmonella Brandenburg organism in sheep plasma was undertaken. Expression of common antigens has resulted in a high level of antibody cross-reactivity between different serovars in serological tests. Lipopolysaccharides (LPS) (O Antigens) are the primary cause of these cross-reactions. Cross-reactivity with two common sheep serovars (Salmonella Typhimurium and Salmonella Brandenburg) was of major concern for the development of a Salmonella Brandenburg ELISA. This was overcome by preparing an antigen mainly composed of flagella and fimbria proteins (LPS free). The antigen preparation was of a relatively crude and non-characterised nature and could only produce a reasonable optical density response at a high concentration. Unfortunately, while the ELISA was responsive, the specificity of the ELISA for Salmonella Brandenburg antibodies remained poor. Further investigation of the specificity of the antigen preparation, through the use of different sera, or through the development of a more pure and specific antigen, is needed for the successful development of a sensitive and specific serological test for determining Salmonella Brandenburg exposure in New Zealand sheep. A case control study was performed as part of a large-scale ongoing investigation aimed at identifying factors associated with Salmonella Brandenburg disease in New Zealand sheep. Details of disease prevalence and farm management methods were collected from two affected regions in southern New Zealand. Associations between possible risk factors and Salmonella Brandenburg were evaluated using odds ratios, with analyses being performed at two different levels: • farm level analysis to compare affected vs. unaffected farms using a case-control approach. • within farm analysis restricted only to affected farms to evaluate risk factors associated with severity of reported disease on affected farms. Data were collected from 405 farms containing a total of 1, 170,737 ewes. Of the 175 case farms, 97% had diseased mixed age (MA) ewes, 45% had diseased two-tooth (TT) ewes, and 5% had diseased hogget (H) ewes. Salmonella Brandenburg appeared to occur in better performing flocks, which are often associated with intensive farming methods. At the farm level, factors such as increased total number of ewes, feeding of hay, and controlled winter grazing appeared to increase the risk of disease. Farming methods such as controlled winter grazing may result in higher stress levels and increase the shedding of Salmonella Brandenburg organisms. This may create a higher risk of exposure in sheep yards and on pasture, resulting in a higher risk of disease. Feeding crop and having hilly terrain decreased the risk of a farm having disease. A protective effect of hilly terrain could be due to less intensive farm management, with a subsequent reduction in stress associated disease risk. Within affected farms, disease appeared to be more severe with the removal of rams after July, feeding of hay, and the practices of strop grazing. Shearing after July, increasing the total number of pre-lamb yardings, and vaccinating for Salmonella appeared to be protective. Therefore reducing stress and vaccinating ewes appear to reduce the risk of a Salmonella Brandenburg outbreak.