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Biomedical subjects

F H Dodd

Publications and source records attributed to F H Dodd.

At least 19 recordsLinked to original sources
PubMed1992

Cost benefit analysis of bovine mastitis in the UK.

Bovine mastitis reduces the yield and quality of milk and increases the rate of culling and veterinary costs. This reduces the profitability of farm milk production but the calculation of the extent of this economic loss is complex because of the many factors involved and deficiencies in the evidence on the relationship between the disease and various production factors. This paper examines the available evidence for the UK and provides a consistent analytical framework within which the benefits arising from reduced mastitis in dairy herds constrained by quota can be considered. It is estimated that since 1970 the farms that have followed the recommended control procedures have reduced the average annual number of cases of clinical mastitis from 135 to 40 cases/100 cows each year, while the quarters remaining uninfected for a whole year has increased from 65 to 80% of the total quarters. The costs of the main control procedures (e.g. 8.60 pounds/cow for dry-cow therapy and teat dipping or spraying) are broadly covered by the reduction in clinical mastitis, leaving the benefits of reduced subclinical infection (e.g. 3810 pounds for a 100 cow herd unconstrained by quota and achieving the average reduction in infection) as a substantial bonus. The imposition of quotas reduces the financial benefit of mastitis control but it still remains a worthwhile investment. The results of this analysis can be used to suggest maximum costs of additional new control measures produced by research. It also indicates that there is considerable value in production research which gives more precise knowledge of production systems, thus allowing producers to respond optimally to quota cuts.

Animals↗
PubMed1988

Consequences of diagnostic errors in mastitis therapy trials.

The effect of errors that occur in the diagnosis of intramammary infectious mastitis on the precision of experiments measuring the efficacy of mastitis therapy has been investigated. Diagnostic errors within the range found by experienced workers can create large biases in the apparent cure rate of therapy particularly at cure rates of less than 0.5. Using confirmed methods of diagnosis rather than single samples and reducing the probabilities of false positive and false negative diagnoses to 0.01 and 0.05 respectively, the biases in the apparent cure rates are reduced to acceptable levels. A method is given for calculating the rates of occurrence of false positive and false negative diagnoses from the results of trials using confirmed diagnoses. These errors cannot be calculated from therapy trial data when diagnosis is based on single milk samples. Because the bias in the measurements of the cure rate is greatest at the lowest levels of elimination, estimates of spontaneous recovery in untreated quarters have the greatest error. For this reason experiments incorporating an untreated control group of infected quarters usually reduce the precision of the therapy trials. An experiment in which the efficacy of a test product is measured relative to a reference product has advantages. It minimizes the difficulties arising from scale of measurement, diagnostic errors and herd differences in response rate, and makes possible comparisons between trials. Further investigations are required on the importance of spontaneous recovery, particularly for studies of Escherichia coli therapy and dry period therapy. The results of this investigation have relevance to all types of mastitis investigation that measure the change in mastitis status of udder quarters, i.e. new infection rates.

Animals↗
PubMed1984

Observations on Corynebacterium bovis infection of the bovine mammary gland. I. Natural infection.

Data from experiments in 55 commercial herds have been examined to study the patterns of Corynebacterium bovis infection. Such infections are most common in herds that are not subjected to regular control methods but their commercial significance appears to be small. In herds using teat disinfection and dry cow therapy levels of infection with this organism are low. There is no evidence from these data to suggest that C. bovis infections protect the udder against invasion by a major pathogen. On the contrary these infections do not persist when major pathogens invade.

Animals↗
PubMed1983

Mastitis--progress on control.

Mastitis has been investigated for over 100 yr, but progress in control has been slow. The reasons for this are complex. Mastitis is caused by several types of infection, each with a different etiology. The possible methods for control are eradication, immunization, therapy, breeding resistant cows, or by improved management factors, but in practice success has been achieved only with the latter. The first practical control was based on specific hygiene methods coupled with the improved use of antibiotic therapy. Later this was augmented by better designs of milking equipment and improved housing. By the control method it is possible to eradicate or reduce to few cows infections caused by staphylococci, Streptococcus agalactiae, and Streptococcus dysgalactiae, but control of Streptococcus uberis is much less effective and coliform mastitis is unaffected. Research indicates that these varying degrees of success are due to basic differences in the various types of infection. There is poor control with infection caused by pathogens that emanate from sources other than the mammary gland and multiply mainly in bedding material (environmental pathogens). Further progress probably depends on the degree of exposure of udders, particularly to these pathogens.

Animal Husbandry↗
PubMed1980

Susceptibility of the bovine udder to bacterial infection in the dry period.

The teats of 18 cows were externally exposed to infection with mastitis organisms by dipping them daily for 1 or 2 weeks in a mixed suspension of Streptococcus dysgalactiae and Str. uberis at the start, the middle or the end of the dry period. The teat sinuses of quarters which remained uninfected after external exposure at the beginning or the middle of the dry period were then infused with the same strains of streptococci. Of the 9 quarters infected following external exposure 8 occurred in animals exposed at the start and one in the middle of the dry period. Thirty-six new infections occurred after infusion of bacteria into the teat sinuses of 38 quarters. In a further trial with 10 cows, Staphylococcus aureus and Str. zooepidemicus were inoculated into the distal 3 mm of the streak canals of 5 cows immediately after drying-off and into those of 5 cows which had been dry for 28 weeks. Animals were slaughtered 48 h later and infection determined by teat puncture. Five infections occurred in cows which were at the start of the dry period and only one in the cows dry for 28 weeks. It is suggested that these differences in the rates of new infection between the early dry period and a very extended dry period are due to differences in the ease with which bacteria can penetrate the teat canal. At the later stage bacterial growth through the teat canal appeared to be inhibited.

Animals↗
PubMed1977

A method of diagnosing intramammary infection in dairy cows for large experiments.

Diagnosis of microbial infections in the udders of cows in commercial dairy farms for large experiments cannot be without error. Limitations of sampling method and routine prevent collection of the necessary information for sure diagnosis. However, with an organized method of repeated bacteriological examinations using consistent and proven methods of aseptic sampling the errors were shown to be very low. A method based on bacteriological tests on aseptic milk samples was used in 32 herds (approximately 2000 cows) for a 3-year period. This is described and examined in terms of other criteria to validate its use in experimental work. With this method it was not difficult to differentiate between those quarters which regularly shed pathogens and those which did not. Other evidence indicated that it was reasonable to assume that this classification accurately distinguished between infected and uninfected quarters. The errors using this method were quite small: when measuring the state of infection of all quarters in the herds the errors did not exceed 1%. Some small modifications to the method described are suggested to improve further its diagnostic accuracy.

Animals↗