Arruda, Andreia Goncalves2013-02-052013-02-052012-12https://hdl.handle.net/11299/143930University of Minnesota M.S. thesis. December 2012. Major: Veterinary Medicine. Advisor: Sandra M. Godden. 1 computer file (PDF); viii, 147 pages.Mastitis remains the most costly infectious disease affecting dairy herds despite the decades of research on its control and prevention. Persistence of preexisting intramammary infections (<bold>IMI</bold>) throughout the dry period and development of new IMI during the dry period are two important factors that influence the risk for manifestation of clinical mastitis in the next lactation. Blanket dry cow therapy (<bold>DCT</bold>) is one strategy that has been highly successful to prevent and control this disease. It is defined as the intramammary treatment of all quarters of all cows with a long-lasting antibiotic formulation at dry off, and it has the purpose of curing preexisting IMI and preventing new IMI that could be potentially acquired during the dry period. Although dry cow antibiotic formulations are widely used in dairy herds across the United States, the efficacy of these products was typically established many years or decades ago, and well-designed head-to-head studies comparing efficacy among DCT products have been largely lacking. The main goal of this multi-herd, multi-state study was to provide producers with information on the relative efficacy of three commercially available DCT products. This information could help guide in the selection of DCT products, thus promoting cow health and welfare, economic sustainability of the dairy farm and judicious drug use. The three products compared in this study were QUARTERMASTER (<bold>QT</bold>, 100,000 IU procaine penicillin G and 1 g dyhydrostreptomycin), SPECTRAMAST DC (<bold>SP</bold>, 500 mg ceftiofur hydrochloride) and ToMORROW Dry Cow (<bold>TM</bold>, 300 mg cephapirin benzathine). Efficacy of the products was assessed at both the quarter and cow level. The first objective of this study was to describe and compare the efficacy of the three aforementioned DCT formulations at the quarter level. The effects of treatment on risk for presence of an IMI after calving, risk for cure of an IMI during the dry period, risk for development of a new IMI during the dry period and risk of a clinical mastitis event between calving and 100 days in milk (DIM) were evaluated separately. The second objective was to describe and compare efficacy of the same three products regarding cow level health and production parameters for the first 100 DIM, including milk production, linear score (<bold>LS</bold>), risk of culling and death, risk for a clinical mastitis case and risk for pregnancy. A total of 1,091 cows (4,364 quarters) from six commercial dairy herds in four different states (CA, IA, MN and WI) were enrolled and randomized to one of the three treatments at dry off. Quarter milk samples were collected for bacterial culture prior to treatment at dry off, at 0 to 6 DIM and at 7 to 13 DIM. All clinical mastitis, pregnancy, culling and death events occurring in the first 100 DIM were recorded by farm staff using an on-farm electronic record keeping system. Dairy Herd Information Association electronic records were used to retrieve consecutive test data regarding milk production, milk composition and LS until 100 DIM, as well as previous lactation milk production and last LS before dry off. The overall crude quarter level prevalence of infection at dry off was 19.2%. The most common pathogen isolated from milk samples at dry off was coagulase negative <italic>Staphylococcus</italic> (53.9%), followed by <italic>Aerococcus</italic> spp. (12.3%) and other <italic>Streptococcus</italic> spp. (7.4%). At the quarter level, there was no effect of treatment on risk for presence of an IMI at 0 to 6 DIM (least square means [<bold>LSM</bold> ]: QT = 0.16 (95% CI: 0.14, 0.19), SP = 0.14 (95% CI: 0.12, 0.17) and TM = 0.16 (95% CI: 0.14, 0.19)), risk for a cure between dry off and calving (LSM: QT = 0.93 (95% CI: 0.87, 0.97), SP = 0.93 (95% CI: 0.86, 0.96) and TM = 0.94 (95% CI: 0.89, 0.97)), risk for development of a new IMI between dry off and 0 to 6 DIM (LSM: QT = 0.15 (95% CI: 0.12, 0.18), SP = 0.12 (95% CI: 0.10, 0.15) and TM = 0.14 (95% CI: 0.12, 0.17)) or risk to experience a clinical mastitis event between calving and 100 DIM (QT = 5.3%, SP = 3.8% and TM = 4.1%). The cow level analysis showed there was no effect of treatment on milk production per day (LSM: QT = 42.9 kg, SP = 42.1 kg and SP = 42.8 kg), milk protein production per day (LSM: QT = 1.21, SP = 1.18 and TM = 1.19), 305 ME (LSM: QT = 11,587 kg, SP = 11,463 kg and TM = 11,540 kg), linear score (LSM: QT = 1.9, SP = 2.0 and TM = 1.7), risk for a clinical mastitis episode (QT = 14.8%, SP = 12.7% and TM = 15.0%), risk for leaving the herd (QT = 7.5%, SP = 9.2% and TM = 10.3%) or risk for pregnancy by 100 DIM (QT = 31.5%, SP = 26.1% and TM = 26.9%). There was an effect of treatment on ECM production (LSM: QT = 41.4 kg <super>a</super>, SP = 40.3 kg <super>b</super> and TM = 41.1 kg <super>a,b</super>, P = 0.0496), FCM production (LSM: QT = 41.9 kg <super>a</super>, SP = 40.7 kg <super>b</super> and SP = 41.7 kg <super>a,b</super>, P = 0.03) and fat production (LSM: QT = 1.44 kg <super>a</super>, SP = 1.39 kg <super>b</super> and TM = 1.43 kg <super>a,b</super>, P = 0.03) by 100 DIM. Contrast analysis showed that cows treated with QT had a trend for higher ECM production by 100 DIM and produced more FCM and milk fat when compared to cows treated with SP. In conclusion, with the exception of ECM, FCM and milk fat production, this study found no difference in efficacy among the three commercial DCT antibiotic formulations evaluated. Dairy farmers and herd managers should consider the findings of this study alongside with other product related characteristics such as dry period length, meat and milk withhold periods and cost, in order to help guide the selection of DCT products for use in their herds.en-USDry cow mastitisDry cow therapyThesis or Dissertation