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 negativecontrolled 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 somatic cell count (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 log 10 -transformed SCC (log 10 SCC) 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 (i) bacteriological cure (negative culture) at period 1 in cows infected at dry-off, and (ii) new intramammary infection 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 log 10 SCC were observed between treatment groups during periods 1 and 2. Nevertheless, when comparing cows infected with Staph.aureus at dry-off, cows treated with the carvacrol-based botanical product showed higher log 10 SCC 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 (Staphylococcus aureus, Staphylococcus chromogenes, other pathogens), as well as the probability of new intramammary infection 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 log 10 SCC, the occurrence of new intramammary infections, 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.