Effect of intramammary infusion of a carvacrol-based botanical product at dry-off on udder health in organic-certified dairy cows.

The aim of this study was to evaluate the effect of intramammary infusion of a carvacrol-based botanical product at dry-off on udder health during the subsequent lactation in Holstein cows managed in an organic-certified system. This randomized negative-controlled trial included 159 Holstein cows calving from May to December 2024 at a commercial organic dairy. Before the final milking before dry-off, composite milk samples were collected for SCC and bacteriological culture diagnosis. Immediately after milking, a carvacrol-based botanical product was intramammarily infused into each quarter in the treatment group, whereas distilled water was infused to the control group. Following calving, composite milk samples were collected during periods 1 (2-14 DIM) and 2 (15-30 DIM). Multivariable mixed linear regression models for repeated measures were used to assess the effect of treatment on log10-transformed SCC (log10SCC) during periods 1 and 2. Multivariable mixed logistic regression models for repeated measures were fitted to evaluate the effect of treatment on the probabilities of (1) bacteriological cure (negative culture) at period 1 in cows infected at dry-off and (2) new IMI at period 1 in cows not infected at dry-off, by treatment group. At dry-off, 47.2% of cows were uninfected, whereas 16.4% and 22.6% were infected with Staphylococcus aureus and Staphylococcus chromogenes, respectively. After calving, these percentages were 56.9%, 18.5%, and 13.9%, respectively. No differences in log10SCC were observed between treatment groups during periods 1 and 2. Nevertheless, when comparing cows infected with S. aureus at dry-off, cows treated with the carvacrol-based botanical product showed higher log10SCC values than those in the control group in period 2. Conversely, the probability of bacteriological cure in cows infected at dry-off with the 3 pathogen groups (S. aureus, S. chromogenes, other pathogens), as well as the probability of new IMI at period 1 in cows not infected at dry-off, were similar between the treatment and control groups. The results indicated that the carvacrol-based botanical product was not effective in reducing either the log10SCC, the occurrence of new IMI, or the recovery of cows infected at dry-off. In conclusion, the intramammary infusion of a carvacrol-based botanical product at dry-off did not improve udder health in the subsequent lactation of dairy cows in an organic-certified system.