Discipline: mastitis; Keywords: selective dry cow therapy, antibiotic use, economics, optimization.
Mastitis in dairy cows is costing the industry. It leads to treatment costs, milk production losses, and early culling of cows. For many years, blanket dry cow therapy (BDCT) has been the accepted treatment in mastitis control. It involves administering long-acting antibiotics to all cows and quarters at dry-off, regardless of their infection status or incidence risk during the dry period. The use of BDCT has been successful in reducing the prevalence of contagious pathogens, and it has contributed to the overall decrease in bulk tank SCC in many countries. In some countries BDCT has been the standard management practice. In others, mastitis has been successfully managed with selective dry cow therapy (SDCT) since the 1970s. With SDCT, dairy cows are selected for antibiotic treatment based on their risk to have an intra-udder infection at the moment of dry-off, as this is an important risk factor for mastitis in the early subsequent lactation. The adoption of SDCT has not changed the SCC dynamics around the dry period, but it has significantly decreased the use of antibiotics. However, early research on SDCT has shown that this approach may result in a greater risk of mastitis in the subsequent lactation. More recent studies, investigating the use of SDCT with teat sealants at dry-off, have shown promising results, with the overall incidence risk of mastitis at calving and in the early subsequent lactation being the same among the group of cows receiving BDCT or SDCT. Economic studies on SDCT have shown that using SDCT can be economically beneficial. However, none of these studies considered the use of internal teat sealants in their analysis and because the use of internal teat sealants at dry-off appeared efficient in preventing new intra-udder infections during the dry period, one of the objectives of the study by Dr N.M.C. Hommels and co-workers was to evaluate the economic feasibility of implementing SDCT with the use of teat sealants. A second objective was to estimate the potential reduction in antibiotic use via SDCT. The results of the study were published in the Journal of Dairy Science, Volume 104 of 2021, page 8931 to 8946. The title is: Antibiotic use and potential economic impact of implementing selective dry cow therapy in large US dairies.
The data were obtained from the Dairy Herd Improvement Association and individual dairy herds in California. Regression models were used to predict the incidence risk of subclinical and clinical mastitis in the subsequent lactation for 96 last test-day somatic cell score categories. Linear programming was used to optimize the costs of dry cow therapy in three simulated large US dairy herds with different bulk tank somatic cell counts (BTSCC). The objective function was aimed at minimization of the total cost of mastitis around the dry period (TCMD), under a varying constraint of the maximum percentage of cows dried off with antibiotics. A sensitivity analysis was performed on milk price, dry-off antibiotic price, and risk ratio of mastitis in the subsequent lactation when no antibiotics and only teat sealant was used at dry-off.
For all situations, blanket dry cow therapy was more expensive than SDCT. In a herd with medium BTSCC, the TCMD was $54.7 per first calf dry cow and $58.5 per multi-lactation dry cow annually. In the optimal economic situation where SDCT was used, only 30% of first calf cows received antibiotics, leading to a TCMD of $52.4 per first calf dry cow, whereas 88% of multi-lactation cows received antibiotics, at a cost of $58.2 per multi-lactation dry cow. This corresponded with an overall reduction of 29% in the use of antibiotics around the dry period for a conservative scenario.
Based on the calculations, it is economically feasible to implement SDCT in large herds, with a potential to reduce the use of antibiotics around the dry period by 29% in a conservative scenario. The largest reduction in the use of antibiotics when applying SDCT could be made in first calf cows. When the percentage of cows receiving antibiotics at dry-off was gradually restricted, the incidence of both subclinical and clinical mastitis increased. In conclusion, it is important to mention that the epidemiology of mastitis pathogens and the dry cow management in each herd be considered before an SDCT strategy is implemented.