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Biomedical subjects

A W Stott

Publications and source records attributed to A W Stott.

At least 19 recordsLinked to original sources
PubMed2005

Assessing economic and social pressure for the control of bovine viral diarrhoea virus.

The objective of this paper is to present a preliminary assessment of variation in the economic impact of bovine viral diarrhoea virus (BVDV) at dairy farm level between a sample of nations within the EU and hence assess differences in pressure to respond to this disease that may be impeding progress in control and hence restricting collective benefits from healthier livestock. We used a questionnaire to obtain national average values of key epidemiological and economic parameters for a typical dairy farm from BVDV experts in the countries concerned. These parameters were converted into assessments of economic impact using a computer simulation model. Uncontrolled output losses for a BVDV-naïve herd with virus introduced in year 1 of a 10-year epidemic represented 22, 7, 8, 5, 8 and 20% of the BVDV-free annuity for the UK, Northern Portugal, Holland, Norway, Italy and Germany, respectively. Differences between countries will be widened by differences in the risk of acquiring BVDV. These will be much reduced in countries, such as Norway that have a national BVDV eradication programme. Farmers in such countries can therefore justify spending much less on maintaining BVDV-free status than BVDV-free farms in other countries. This result illustrates the paradox that in countries where BVDV prevalence is high, farmers have least to gain from unilateral BVDV eradication because of the high cost of maintaining freedom from the disease. We discuss this issue in the light of increasing recognition at international level of the importance of BVDV control.

Animals↗
PubMed2005

Optimal risk management versus willingness to pay for BVDV control options.

Previous work has shown that the least-cost BVD-control option for cow-calf herds in Scotland was not necessarily the risk-minimising option. Thus, assessing BVDV prevention measures must account for risk reduction as well as decision-makers' attitude towards risks. We therefore describe a method to do this using a hypothetical example. Data for this analysis were generated using a simulation model of BVDV transmission in a typical Scottish cow-calf herd over a 10-year period. Herd infection/re-infection was adjusted to reflect the expected risk of infection/re-infection and the use of either biosecurity or vaccination strategies at various levels of effectiveness. The level of risk-free financial return that maximises farmers' utility of wealth was significantly affected by the assumed effectiveness of the control strategy. More importantly, it was observed that utility maximisation of wealth as a business objective is not an optimal solution in terms of animal welfare when dealing with a BVDV outbreak.

Agriculture↗
PubMed2005

A model of the relationship between the epidemiology of Johne's disease and the environment in suckler-beef herds.

A non-predictive, dynamic and stochastic herd-level simulation model of an outbreak of Johne's in a suckler-beef herd is reported. Importantly, the model incorporates, with a simple method, the environment as the primary source of infection, reflecting the consensual understanding of the disease. The model also takes into account the density of the infectious agent in the environment. A sensitivity analysis suggests that the model is highly and equally sensitive to certain parameters (probability of infection in the presence of one unit of bacterial density, infectious area and bacterial shedding rate). Mathematical reasons for this similarity in sensitivity are presented. Compared to many other diseases, data for Johne's are scarce. Therefore models of Johne's outbreaks including this one cannot be predictive or easily validated. The qualitative results: (a) demonstrate the modelled effect of inclusion of infection via the environment; (b) suggest management factors that could be tested by experimentation or observation. Estimates for the rate of transmission, arising from the model output, are similar to published empirical estimates. The results of future empirical research should aid scientific understanding of the disease, help validate this model and might bring economic benefits through improved management.

Age Factors↗
PubMed2005

Financial incentive to control paratuberculosis (Johne's disease) on dairy farms in the United Kingdom.

This paper estimates the financial incentive to control paratuberculosis on dairy farms by establishing the level of expenditure that would minimise the total cost of the disease (output losses plus control expenditure). Given the late onset of the clinical signs and the lack of treatments, control was focused on minimising the financial impact of paratuberculosis by adjusting the dairy cow replacement policy. The optimum replacement policies for disease-free herds and infected herds were compared by using dynamic programming. At the standard settings, the disease justified adjusting the culling policy; under constant bioeconomic assumptions, it reduced the expected annuity from milk production under the optimal replacement policy by about 10 per cent (27 pounds sterling per cow annually), a considerably lower figure than for other major endemic diseases that affect dairy cows in the uk. The effect was even less at lower milk prices, suggesting that there is at present little incentive for dairy farmers to put more resources into controlling the disease. However, the incentive could be increased if more information were available about how best to manage the disease under specific farm circumstances. Any effect that paratuberculosis may have on the future demand for milk and hence on milk prices would also be an important consideration.

Animals↗
PubMed2004

Modelling and costing BVD outbreaks in beef herds.

Results from an epidemiological model of an outbreak of Bovine Viral Diarrhoea (BVD) within a Scottish beef suckler herd are presented. These results concurred with field observations and encouraged us to fulfill the objective of providing an estimate of losses due to BVD to assist decision makers. Using the output from the model, estimates were made of losses associated with the outbreak. Without taking into account any financial premiums associated with disease-free status, the estimate of pound 37 (58) mean loss per cow per annum suggests that health schemes and vaccination should be of immediate financial interest to farmers and veterinary advisors.

Animals↗
PubMed2003

A linear programming approach to estimate the economic impact of bovine viral diarrhoea (BVD) at the whole-farm level in Scotland.

We combined epidemiological and economic concepts and modelling techniques, to integrate animal health into whole-farm business management. This allowed us to assess the relative contribution that disease prevention could make to whole-farm income and to the variability in farm income (risk). It also allowed us to assess disease losses in the context of a farm business rather than as a disease outbreak in isolation. A linear program ("MOTAD") establishes the combination of decision maker's activities that minimise risk for a given level of income within farm-business constraints. The MOTAD model was applied to farm-management decision making in Scottish cow-calf herds and was linked to an epidemiological model of bovine viral diarrhoea (BVD). When BVD was considered in isolation (i.e. without taking into account risk), the minimum expected total cost of BVD (sum of output losses plus expenditure on prevention) was similar whether the herd was susceptible to BVD or of unknown BVD-status at the outset. However, the expected total cost of BVD fell in response to increasing expenditure on prevention in 'susceptible' herds. This relationship was not apparent in herds of unknown BVD-status. As a consequence of this difference, 'susceptible' herds were better able to use investment in BVD biosecurity as a means to increase farm income at minimum risk than herds of unknown BVD-status. 'Susceptible' herds therefore were able to achieve high income targets with less-intensive production than herds of unknown BVD-status. This suggested that maintaining a cow-calf herd free of BVD contributes to farm income and risk management indirectly through its effect on the management of the whole farm. It follows that measurement of the economic impact of BVD requires a whole-farm perspective that includes a consideration of risk. Because farmers generally are considered to be risk adverse, this means that the least-cost disease-control option might not always be the preferred option.

Agriculture↗
PubMed2000

Dynamic programming to investigate financial impacts of mastitis control decisions in milk production systems.

An adaptive stochastic dynamic programming model was used to solve the optimum replacement decision problem for the dairy cow under a range of alternative mastitis control procedures. The model predicted that reducing milk yield losses and somatic cell count penalties by, using milking machine test, post-milking teat disinfection and dry cow therapy added approximately pounds sterling 4, pounds sterling 10 and pounds sterling 13 respectively to an original annuity equivalent net present value for the replacement heifer of pounds sterling 286. Assuming that these procedures also reduced involuntary culling due to mastitis by 50% added pounds sterling 8.90 to the annuity. This latter figure indicated that an important part of the benefit of mastitis control procedures might come from a reduction in the culling risk of persistent clinical cases. We concluded that the strength of the dynamic programming model in this context was that it provided an integrated evaluation of the various impacts of each alternative mastitis procedure in the long term, which is essential for correct economic evaluation of mastitis.

Animals↗
PubMed1999

The economic impact of mastitis-control procedures used in Scottish dairy herds with high bulk-tank somatic-cell counts.

We used multiple-regression analysis of field data to quantify the marginal impacts of various mastitis-control procedures on bulk-tank somatic-cell count (BTSCC). Estimates of milk-yield depression and the probability of herds paying a BTSCC penalty due to the presence of subclinical mastitis were made. An assessment of the economic efficiency of mastitis control by high BTSCC producers was also made using a loss-expenditure frontier. Significant interactions were detected between premilking udder-preparation methods (UP) and post-milking teat disinfection (PMTD), and also between the milking system of the herds and both the use of dry-cow therapy (DCT) and a regular milking-machine test (MMT). Udder preparation involving washing was associated with a higher SCC and had a detrimental effect on the efficacy of PMTD. Amongst herds facing a high-BTSCC problem (BTSCC >400,000 cells/ml), herds using PMTD without UP (regardless of the type of milking system), those using DCT (in parlour systems), and those with a parlour system having their milking machines tested obtained returns of Pound Sterling 1.4, Pound Sterling 3.9 and Pound Sterling 1.1, respectively, per Pound Sterling 1 investment in each of these procedures as a result of reductions in milk-yield losses and BTSCC penalties. The minimum total cost of disease within these herds was Pound Sterling 65.50/cow/year (due to Pound Sterling 41.40 revenue losses plus Pound Sterling 24.10 mastitis-control expenditure) attained by herds which had a parlour system and used DCT, MMT and PMTD (without UP). However, the average cost of subclinical mastitis for all high-BTSCC farms was Pound Sterling 100/cow/yr; hence, the difference (pound Sterling 34.50) could be saved by the more-efficient application of mastitis-control procedures.

Animal Husbandry↗
PubMed1999

Studies of organic residues from ancient Egyptian mummies using high temperature-gas chromatography-mass spectrometry and sequential thermal desorption-gas chromatography-mass spectrometry and pyrolysis-gas chromatography-mass spectrometry.

The techniques of gas chromatography-mass spectrometry (GC-MS) and sequential thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) have been utilised to characterise the constituents of tissue-derived or applied organic material from two Pharaonic Egyptian mummies with a view to identifying embalming practices/substances. The results obtained using TD-GC-MS revealed a series of monocarboxylic acids with the C16:0, C18:1 and C18:0 components dominating in both mummies. The thermal desorption products related to cholesterol, i.e., cholesta-3,5,7-triene and cholesta-3,5-diene (only in Khnum Nakht), were detected in both mummies. Khnum Nakht also contained a number of straight chain alkyl amides (C16-C18) and an alkyl nitrile (C18). Other products included the 2,5-diketopiperazine derivative (DKP) of proline-glycine (pro-gly) which was a major component (7.9%) in Khnum Nakht but only a very minor component in Horemkenesi. Py-GC-MS of samples of both specimens yielded a series of alkene/alkane doublets (Horemkenesi C6-C18, Khnum Nakht C6-C24) which dominated their chromatograms. Series of methyl ketones in the C9-C19 chain length range were also present, with C5-C7 cyclic ketones occurring in Horemkenesi only. These ketones are indicative of covalent bond cleavage, probably of polymerised acyl lipids. Nitrogenous products included nitriles (C9-C18) which were significant in both samples, and amides which were only detected in Khnum Nakht. Also present amongst the pyrolysis products were three steroidal hydrocarbons, cholest-(?)-ene, cholesta-3,5,7-triene and cholesta-3,5-diene. High temperature-GC-MS of trimethylsilylated lipid extracts yielded similar monocarboxylic acids to that obtained using TD-GC-MS, while a series of alpha, omega-dicarboxylic acids and a number of mono- and di-hydroxy carboxylic acids not seen in the thermal desorption or pyrolysis GC-MS analyses were significant constituents in both mummy samples. Overall, the use of GC-MS and sequential TD-GC-MS and Py-GC-MS has demonstrated in both mummies the presence of a complex suite of lipids and proteinaceous components whose compositions indicates extensive alteration via oxidative and hydrolytic processes during long-term interment. None of the classical embalming resins was detected but an exogenous origin for at least a proportion of these components cannot be discounted since fats, oils and gelatin have been proposed as embalming agents in mummification. The combined approach of sequential TD- and Py-GC-MS has potential for application to the characterisation of embalming materials in mummies. Most importantly these techniques virtually eliminate any destruction of the mummified bodies thereby allowing the scope of investigations of ancient Egyptian funerary practices to be significantly extended.

Embalming↗
PubMed1996

delta 13C analysis of cholesterol preserved in archaeological bones and teeth.

Cholesterol preserved in archaeological bones and teeth constitutes an important new source of palaeodietary information. A method is described here for the isotopic (delta 13C) determination of cholesterol employing a semiautomated sample preparation procedure and the technique of isotope ratio monitoring/gas chromatography/ mass spectrometry (irm/GC/MS). High-temperature gas chromatography (HT-GC) and high-temperature gas chromatography/mass spectrometry (HT-GC/MS) were used to identify the lipids and quantify the cholesterol present in the total lipid extracts. delta 13C values are then readily obtained from nanogram amounts (approximately 50 ng) of cholesterol resolved and determined directly by high-resolution capillary irm/GC/MS of trimethylsilylated total lipid extracts. The protocol developed allows effective processing of the large numbers of samples essential for palaeodietary determinations. Analytical precision and reproducibility have been assessed through multiple sampling of the same skeleton (femur, 9th century). Comparable delta 13C values have been obtained from different skeletal members from the same individual. The utility of the approach is demonstrated through a study of the delta 13C values of cholesterol isolated from sections of femoral bones of individuals excavated from cemeteries (dated Saxon to 18th century) at a coastal site in the U.K. The mean delta 13C value (-22.2 +/- 0.3/1000, sigma = 0.9) determined for cholesterol in 50 different individuals indicates a strong preference for marine foods by the members of the community extending back over the last approximately 1500 years. A minority of individuals exhibited delta 13C values as low as -26/1000, indicating preferences for terrestrial rather than marine foodstuffs.

Archaeology↗
PubMed1993

The economics of culling dairy cows with clinical mastitis.

Culling dairy cows with clinical mastitis reduces the incidence of the disease in dairy herds, but the costs of such action, in terms of reduced milk production and increased replacement costs, are generally thought to outweigh the benefits. To test this hypothesis a stochastic dynamic programming model was developed to establish the economically optimum time of replacement for dairy cows subject to variable levels of clinical mastitis infection, using average United Kingdom production and price parameters. The optimal stage at which to replace a dairy cow was found to be sensitive to changes in mastitis incidence and in critical price parameters within the bounds of commercial experience. This result indicates that an objective culling policy based on clinical mastitis records in addition to milk production potential may be economically viable.

Animals↗
PubMed1980

A simple chromatographic technique for the estimation of urinary levels of normetadrenaline and metadrenaline.

A simple, but effective, procedure is described for the concurrent estimation of normetadrenaline (NMA) and metadrenaline (MA) in urine. The 3-methoxycatecholamines are adsorbed by a cation exchange resin, desorbed, separated by paper chromatography, and finally estimated spectrophotometrically after oxidation to vanillin. The mean (+/- 2 standards deviations) urinary outputs of NMA and MA from 123 normals (80 males, 43 females) in 24 hours was 2.15 +/- 1.04 and 1.79 +/- 0.96 mu mol respectively. There was no significant difference in the 24-hour urinary outputs of NMA between the male and female groups. However, the output of MA from the males was significantly higher than that from the females.

Adult↗
PubMed1975

A simple chromatographic procedure for the concurrent estimation of urinary 4-hydroxy-3-methoxymandelic acid (HMMA) and homovanillic acid (HVA) using a scanning technique.

A rapid and simple procedure is described for the concurrent determination of 4-hydroxy-3-methoxymandelic acid (HMMA) and homovanillic acid (HVA). The acids are separated by chromatography and estimated by a scanning technique. The urinary output of HMMA and HVA over 24 h from 123 normals (80 males, 43 females) gave mean values of 3.3 +/- 0.94 and 4.9 +/- 1.3 mg, respectively. There was no significant difference in the 24 hour urinary output of HMMA and HVA between the male and femal groups.

Chromatography, Paper↗