| Popis: |
Based on proving non-inferiority of one product compared to another, this study was designed to compare the efficacy of an experimental pre-milking teat dip against a positive control in reducing naturally occurring intramammary infections (IMI). To test this methodology in the field, 199 cows were randomly allocated to two groups (Control, CG; n=100 and Experimental, EG; n=99) in Spring/Summer 2010. Personnel were blinded as to the origin of the product. Cows were milked two times per day following standard pre-milking procedures. Quarters of CG and EG cows were pre dipped for 30 sec with the control product and experimental products, respectively. Both different products were 0.5% iodine and 5% emollient. After milking, both groups were dipped with the control product. Quarter milk samples were collected for SCC analysis, at the beginning of the trial and afterwards every two weeks until 70 d. Quarter-level bacteriological status was established in all quarters at the beginning of the study. Milk samples collected thereafter were cultured only if SCC was >100,000 cells/ml in heifers and >200,000 cells/ml in cows. Logistic and linear regressions were used for data analysis. Overall, 148 CG (7.1%) and 130 EG (6.3%) milk samples were bacteriologically positive. Staphylococcus spp. (3.6% of tested samples tested), and Staphylococcus aureus (1.2% of tested samples) were commonly isolated in both groups. Streptococcus uberis was frequently isolated in CG (0.9% vs. 0.2% in EG). SCC geometric means were 32,000 (CG) and 25,000 (EG) cells/ml. No differences between groups in the log odds of having either an IMI or a new IMI (NIMI) were observed. The critical difference in the NIMI rate between both products was set at 0.03. The observed difference in NIMI rate was negligible, showing a non-inferiority of the experimental product vs. control. This study provided evidence of a valid and field-tested methodology to evaluate the efficacy of teat disinfectants under the assumption of non-inferiority. |
