Efficacy of on-farm programs for the diagnosis and selective treatment of clinical and subclinical mastitis in dairy cattle.

University of Minnesota Ph.D. dissertation. August 2009. Major: Veterinary Medicine. Advisor: Sandra M. Godden. 1 computer file (PDF); xv, 264 pages.The research reported in this dissertation includes two multi-state multi-herd clinical trials evaluating the efficacy of on-farm programs for the diagnosis and selective treatment of clinical and subclinical mastitis in dairy cattle. The use of an OFC system for the selective treatment of clinical mastitis during lactation reduced intramammary antibiotic use by half and tended to reduce withholding time by one day, without significant differences in days to clinical cure, bacteriological cure risk, new infection risk and ICR risk (where the ICR risk represented the presence of infection risk, clinical mastitis risk, or removal from herd risk) within 21 days after the clinical mastitis event. Similarly, there were no differences between both treatment programs in long-term outcomes such as recurrence of clinical mastitis in the same quarter, somatic cell count, milk production, and cow survival for the rest of the lactation after the clinical mastitis event. The treatment with intramammary Cephapirin Sodium of cows and quarters based on CMT results alone, or sequential testing using OFC to diagnose Gram-positives in CMT-positive quarters resulted in a higher bacteriological cure risk and reduced the ICR risk within 21 days after enrollment (significantly and only numerically, respectively for treatment each program). The implementation of both treatment programs required the administration of intramammary treatment and extended the time that milk is withhold from the market. Both programs resulted in a significantly lower clinical mastitis risk and lower milk SCC during lactation (significantly and only numerically, respectively for each treatment program). However, the implementation of both treatment programs did not result in higher milk production, improved reproductive performance or lower risk for removal from the herd. A secondary objective of both clinical trials was to validate the use of the Minnesota Easy Culture Bi-Plate System. This OFC system is a useful cow-side test to correctly identify bacterial growth, Gram-positive bacterial growth, or Gram-negative bacterial growth in quarter secretion samples from clinical mastitis cases and in CMT-positive quarter milk samples collected after parturition. Treatment decisions based on identification of bacterial growth, or Gram-positive bacterial growth specifically, were correct over 73% of the time