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Introduction Development of control methods Antibiotic therapy Hygiene Control schemes Milking machine research Mastitis awareness The value of current control methods Aetiology of mastitis Staphylococcus aureus Streptococcus agalactiae Streptococcus dysgalactiae Streptococcus uberis Coliforms Pseudomonas aeruginosa Mycoplasma bovis Corynebacteria General characteristics of bovine mastitis Stages in the infection process Exposure to pathogenic microorganisms CONTENTS PAGE 481 482 482 483 483 484 484 485 486 486 486 487 487 487 488 488 488 489 489 490 Penetration of the teat duct by pathogens Establishment of an intramammary infection Parasite factors Host factors Cellular and immune defence of the udder Nonspecific defence mechanisms Elimination of infections Culling Spontaneous recovery from infection Antibiotic therapy Dynamics of infection in dairy herds Effects of mastitis monitoring systems on awareness and control Conclusions References * Grant aided by the Agricultural and Food Research Council.

Methods of drying-off cows at the end of each lactation period may have a relatively important influence on the establishment of infections of the udder and on latent infections; this has been pointed out by Munch-Petersen(i) and by Steyn(2). There is still, however, little information about the numbers, types and duration of infections occurring in the drying-off and dry periods and the influence of these infections on milk yield in the subsequent lactation.In the present study of new infections in the dry period, data have been collected over a period of 3 years in an attested Shorthorn herd (herd N) free from contagious abortion. In the 3 years 1946-8 the average weekly number of cows in milk and the average age of the herd in lactations were 45-4, 49-8, 47-7 and 2-75, 2-48 and 2-34 respectively. The total number of cows infected with Streptococcus agalactiae in these years was 16, 11 and 5, with other streptococci 7, 10 and 12, and with staphylococci 6, 19 and 35. From May 1946 clinical cases only were treated with penicillin. METHODSWhen the daily milk yield had dropped to 8-10 lb. the animals were dried off in 1 week by intermittent milking, i.e. by milking the udder out once a day for 1 week only. Once the cows ceased to be milk-recorded no fluid was drawn except for the small quantities of secretion needed for the bacteriological examination.Fore-milk samples were taken from each quarter 3 days before the final milking-out of the udder, 7, 14 and 21 days later, about 1 week before calving and on the day of calving. Subsequent samples were taken from all quarters of non-infected cows on the 7th and 10th days after calving and from infected cows on the 3rd, 5th, 7th and 10th days. During lactation samples were taken at intervals of 1-2 months or more frequently.Both during lactation and in the dry period any change in the bacteriological state of the udder was followed by one or more confirmatory samples.One-ounce samples -were taken during lactation, and 1-5 ml. samples during the dry period. From the vast majority of dry cows no difficulty was experienced in obtaining sufficient secretion for bacteriological examination. The few cases of difficulty were caused by the absence of detectable amounts of secretion and not by difficulty in expressing it.Until May 1946, the herd was milked by hand. Subsequently, part of the herd was milked by a bucket-type milking machine and carefully stripped by machine. From September 1946 the herd was machine-milked, though a few cows were hand-milked throughout 1947.The hands of milkers were not washed before milking each cow and disinfectants were not used for udder washing throughout the period under review, though dipping the teat

SummaryIn each of 5 cows, 2 quarters which had been regularly milked throughout the whole of pregnancy produced less milk in the next lactation than the other 2 quarters which had a normal dry period. The concentrations of the individual constituents in the milk of all 4 quarters of each cow were similar. The effect appears to be due to factors located within the individual quarter of the mammary gland rather than to factors such as the hormonal background or plane of nutrition which affect the whole animal.

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