Randomized controlled trial investigating the effect of 2 selective dry-cow therapy protocols on udder health and performance in the subsequent lactation

摘要

The objective of this study was to compare cultureandalgorithm-guided selective dry-cow therapy (SDCT)programs with blanket dry-cow therapy (BDCT) in amulti-site, randomized, natural exposure clinical trialfor the following cow-level outcomes: clinical mastitis,removal from the herd, and Dairy Herd ImprovementAssociation (DHIA) test-day milk yield and SCC measuresduring the first 120 d in milk (DIM). Two daysbefore planned dry-off, cows in each of 7 herds wererandomly allocated to BDCT, culture-guided SDCT(cult-SDCT), or algorithm-guided SDCT (alg-SDCT).At dry-off, BDCT cows received an intramammaryantibiotic (500 mg of ceftiofur hydrochloride) in all 4quarters. Antibiotic treatments were selectively allocatedto quarters of cult-SDCT cows by only treatingquarters from which aseptically collected milk samplestested positive on a rapid culture system after 30 to40 h of incubation. For alg-SDCT cows, antibiotictreatments were selectively allocated at the cow level,with all quarters receiving antibiotic treatment if thecow met at least one of the following criteria: (1) anyDHIA test with a somatic cell count >200,000 cells/mL during the current lactation, and (2) ≥2 clinicalmastitis cases during the current lactation. All quartersof all cows were treated with an internal teat sealant.Clinical mastitis and removal from the herd events (i.e.,culling or death) and DHIA test-day data from dry-offto 120 DIM were extracted from herd records. Hazardratios (HR) for the effect of treatment group on clinicalmastitis and removal from the herd during 1 to 120DIM were determined using Cox proportional hazardsregression. The effects of treatment group on test-dayloge-transformed SCC and milk yield were determinedusing linear mixed models. Final models indicated thateither SDCT program was unlikely to increase clinicalmastitis risk (HR_(cult-SDCT/BDCT) = 0.82, 95% CI: 0.58,1.15; HR_(alg-SDCT/BDCT) = 0.83, 95% CI: 0.63, 1.09) ortest-day logeSCC (cult-SDCT minus BDCT = 0.05,95% CI: −0.09, 0.18; alg-SDCT minus BDCT = 0.07,95% CI: −0.07, 0.21). Risk of removal from the herdand test-day milk yield were similar between treatmentgroups. Findings from this study indicate that cultureoralgorithm-guided SDCT can be used at dry-off withoutnegatively affecting cow health and performance inearly lactation.