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Title: The relationship between bovine mastitis and somatic cell counts in dairy herds in Scotland
Author: Gunn, John
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1995
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Thirty-five dairy herds were investigated in a three-year study of high Bulk Tank Somatic Cell Count (BTSCC). Streptococcus agalactiae was isolated from 19 (83%) of 23 herds selected initially as being representative of all those in Scotland with such a milk quality problem. In this group it accounted for 57% of all isolates of the major mastitis-causing pathogens with Staphylococcus aureus (29%) the second most frequent isolate. All these herds were selected for investigation using an "MQFILE" personal computer database which allowed the first scientific analysis of the national epidemiology of SCC in Scotland. Previously herd BTSCC data was retained on a mainframe computer for only a rolling 12 month period and was not subjected to detailed analysis. High BTSCC herds in Scotland were found to make a major contribution to national production and thus could not be ignored. An almost linear relationship was demonstrated between their annual mean BTSCC and the number of months over the 400,000 EC threshold. This indicated that an annual mean BTSCC target of less than 250,000 was required to avoid exceeding this threshold throughout the year and particularly in the autumn. A new database ("CCGM") format was established to store and analyse Individual Cow SCC (ICSCC) data from successive herd-tests. These herd investigations were the first in the UK to use a "Linear Score" (LS) 5-1+ (over 283,000) ICSCC threshold calculated by "CCGM" to select infected cows and thus reduce the cost of bacteriological examination. This threshold was selected by the analysis of historical data from whole herd bacteriological examinations conducted by SAC Aberdeen. This analysis revealed that a significant isolate was recovered from only 27.4% of all composite samples but that infection by any of the major mastitis pathogens was the most important cause of raised SCC in both Individual Cow (IC) and Quarter (Q) samples. This SCC increase caused by infection was very significant (P < 0.001) irrespective of stage of lactation or lactation number and thus allowed the identification of carrier cows. Herd-specific mastitis control advice was then formulated using the CCGM-ICSCC and bacteriological profiles from each investigation. A large questionnaire study which examined the relationship between management practices and BTSCC illustrated the very significant (P < 0.001) advantages of the "five point" mastitis control plan and membership of the Scottish Milk Records Association. The more comprehensive data from project herds showed that the adoption of paper-towels in premilking udder preparation was associated with a very significant (P < 0.001) reduction in BTSCC. The group mean of these "assisted" project herds was very significantly (P < 0.001) less than their contemporaries. Thus the adoption of the mastitis control recommendations had successfully achieved control of subclinical mastitis which was economically worthwhile. It is estimated that these assisted herds actually gained £33/cow/year in gross margin. All producers in Scotland have received advisory literature developed from this study by direct mailing. The study has allowed the development of an integrated system for the investigation and control of high BTSCC problem herds in Scotland.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available