Department of Veterinary Population Medicine, University of Minnesota, St. Paul 55108.
Department of Veterinary Population Medicine, University of Minnesota, St. Paul 55108.
J Dairy Sci. 2020 Jul;103(7):6493-6503. doi: 10.3168/jds.2019-17961. Epub 2020 Apr 22.
The objective of this study was to compare culture- and algorithm-guided selective dry-cow therapy (SDCT) programs with blanket dry-cow therapy (BDCT) in a multi-site, randomized, natural exposure clinical trial for the following cow-level outcomes: clinical mastitis, removal from the herd, and Dairy Herd Improvement Association (DHIA) test-day milk yield and SCC measures during the first 120 d in milk (DIM). Two days before planned dry-off, cows in each of 7 herds were randomly allocated to BDCT, culture-guided SDCT (cult-SDCT), or algorithm-guided SDCT (alg-SDCT). At dry-off, BDCT cows received an intramammary antibiotic (500 mg of ceftiofur hydrochloride) in all 4 quarters. Antibiotic treatments were selectively allocated to quarters of cult-SDCT cows by only treating quarters from which aseptically collected milk samples tested positive on a rapid culture system after 30 to 40 h of incubation. For alg-SDCT cows, antibiotic treatments were selectively allocated at the cow level, with all quarters receiving antibiotic treatment if the cow met at least one of the following criteria: (1) any DHIA test with a somatic cell count >200,000 cells/mL during the current lactation, and (2) ≥2 clinical mastitis cases during the current lactation. All quarters of 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-off to 120 DIM were extracted from herd records. Hazard ratios (HR) for the effect of treatment group on clinical mastitis and removal from the herd during 1 to 120 DIM were determined using Cox proportional hazards regression. The effects of treatment group on test-day log-transformed SCC and milk yield were determined using linear mixed models. Final models indicated that either SDCT program was unlikely to increase clinical mastitis risk (HR = 0.82, 95% CI: 0.58, 1.15; HR = 0.83, 95% CI: 0.63, 1.09) or test-day logSCC (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 herd and test-day milk yield were similar between treatment groups. Findings from this study indicate that culture- or algorithm-guided SDCT can be used at dry-off without negatively affecting cow health and performance in early lactation.
本研究的目的是在多地点、随机、自然暴露临床试验中比较培养物指导和算法指导的选择性干奶牛疗法（SDCT）方案与 blanket dry-cow therapy（BDCT）方案，以评估奶牛水平的以下结果：临床乳腺炎、从牛群中移除和 Dairy Herd Improvement Association（DHIA）在干奶前 120 天内的产奶量和 SCC 测量值。在每个 7 个牛群中，在计划干奶前两天，随机将奶牛分配到 BDCT、培养物指导的 SDCT（cult-SDCT）或算法指导的 SDCT（alg-SDCT）。在干奶时，BDCT 牛群的所有 4 个乳区都接受了 500 毫克头孢噻呋盐酸盐的抗生素治疗。仅对 cult-SDCT 奶牛的乳区进行抗生素治疗，这些乳区在 30 至 40 小时的孵育后，通过快速培养系统检测到无菌采集的牛奶样本呈阳性。对于 alg-SDCT 奶牛，根据以下至少一个标准，在牛群水平上进行抗生素治疗：（1）当前泌乳期内任何一次 DHIA 检测的体细胞计数>200,000 个细胞/ml，以及（2）当前泌乳期内发生≥2 例临床乳腺炎病例。所有奶牛的所有乳区都接受了内部乳头密封剂的治疗。从干奶到 120 天产奶期的临床乳腺炎和从牛群中移除的事件（即淘汰或死亡）和 DHIA 测试日数据从牛群记录中提取出来。使用 Cox 比例风险回归确定治疗组对 1 至 120 天内临床乳腺炎和从牛群中移除的风险的影响的风险比（HR）。使用线性混合模型确定治疗组对测试日对数转换 SCC 和产奶量的影响。最终模型表明，任何一种 SDCT 方案都不太可能增加临床乳腺炎的风险（HR=0.82，95%CI：0.58，1.15；HR=0.83，95%CI：0.63，1.09）或测试日对数 SCC（cult-SDCT 减去 BDCT=0.05，95%CI：-0.09，0.18；alg-SDCT 减去 BDCT=0.07，95%CI：-0.07，0.21）。治疗组之间的淘汰风险和产奶量相似。这项研究的结果表明，在干奶时可以使用培养物指导或算法指导的 SDCT，而不会对奶牛在泌乳早期的健康和性能产生负面影响。
