Randomized noninferiority field trial evaluating a postmilking teat dip for the prevention of naturally occurring intramammary infections

The aim of this study was to perform a positive-controlled field study under natural exposure conditions to test the efficacy of a newly developed chlorine dioxide-based postmilking teat disinfectant (experimental product, EX) for noninferiority compared with an already established chlorine dioxide-based teat disinfectant (positive control product, PC). After blocking by parity, approximately 200 Holstein cows in early to mid-lactation stages from a dairy farm near Padua, Italy, were randomly assigned to one of 2 groups. Over a 13-wk period between September and December 2021, the teats of cows were dipped with the EX or the PC after each milking. Milk samples were collected from individual quarters of enrolled cows for 13 wk to determine infection status. Teat condition was assessed at wk 1, 5, and 9. Mixed logistic regression was used to analyze the effect of treatment on the incidence of new intramammary infections. For the noninferiority analysis, the upper limit of the 95% confidence interval for the difference in new intramammary infection (NIMI) rate between the 2 treatments (EX − PC) had to be to the left of the critical value d (0.035) to conclude that EX was noninferior to PC in terms of the risk of NIMI. The results showed that the incidence of new infections in the quarters treated with EX (3.1%) was not different from that in the udder quarters treated with PC (2.6%). No overall difference was found between the treatments in terms of teat condition. As the upper limit of the 95% confidence interval of the NIMI rate difference was smaller than the predefined noninferiority limit, we concluded that the EX was noninferior compared with the PC.