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Field trials of a vaccine against bovine mastitis . 1 . Evaluation in heifers . A vaccine was developed against bovine mastitis based on inactivated , highly encapsulated Staphylococcus aureus cells ; a crude extract of Staph . aureus exopolysaccharides ; and inactivated , unencapsulated Staph , aureus and Streptococcus spp . cells . This vaccine was tested on 30 heifers during a 7-mo period . The 30 heifers were randomly assigned to three groups of 10 heifers each . The prepartum group received two injections of the vaccine at 8 and 4 wk before calving , and the postpartum group received two injections at 1 and 5 wk after calving . The control group received two injections of a placebo at 8 and 4 wk before calving . The vaccine or the placebo was administered subcutaneously in the brachiocephalicus muscle of the neck . The frequencies of intramammary infections caused by Staph . aureus were reduced from 18.8 % for heifers in the control group to 6.7 and 6.0 % for heifers in the prepartum and postpartum groups , respectively . This protective effect was maintained for at least 6 mo . The relative risk of mastitis caused by Staph . aureus was 0.31 and 0.28 for heifers in the prepartum and postpartum groups , respectively , compared with that for heifers in the control group . The results of the trial indicated the effectiveness of the vaccine in decreasing the incidence of intrammammary infections caused by Staph . aureus . A slight but nonsignificant increase occurred in fat production in the milk of vaccinated cows . The vaccine had no observable effect on somatic cell count or streptococcal infections .
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Intervention_Pharmacological
vaccine
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Intervention_Pharmacological
vaccine
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Intervention_Pharmacological
vaccine
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Intervention_Pharmacological
vaccine
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Intervention_Pharmacological
vaccine
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Intervention_Control
placebo
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Outcome_Physical
frequencies of intramammary infections caused by Staph
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Outcome_Physical
aureus
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Outcome_Other
protective effect
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Outcome_Physical
relative risk of mastitis caused by Staph
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Outcome_Physical
aureus
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Outcome_Other
results of the trial indicated the effectiveness of the vaccine
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Outcome_Physical
fat production
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Participant_Sex
heifers
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Participant_Sex
heifers
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Participant_Sex
heifers