Observational study on application of a selective dry-cow therapy protocol based on individual somatic cell count thresholds

Selective dry cow therapy (SDCT) is one measure suggested to reduce the use of antibiotics on dairy farms. This procedure may have a negative impact on dairy herds, affecting both milk yield and quality. The aim of this observational study was to evaluate the implementation of a SDCT protocol based on the treatment only of cows with SCC at last individual milk test before drying-off >100,000 cells/mL (primiparous cows) or >200,000 cells/mL (pluriparous cows) on udder infection status. We also assessed the association between cow and management factors with the likelihood of cure or of new IMI across the dry period. The study considered 516 dairy cows (2064 quarters), and only 53% of the cows were treated with antibiotics. Before drying-off, 999 quarters (49.1%) were bacteriological negative at two consecutive samples. After calving the negative quarters were 1004 (49.3%). The likelihood of a cure across the dry period was significantly associated with parity, drying-off length and teat sealant application, while the likelihood of new IMI across the dry period was associated to all the risk factors considered (parity, dry period length, teat sealant application, infections status at drying-off and type of long-acting antibiotic applied). The application under field conditions of the proposed SDCT protocol showed to feasible, and to largely reduce the use of antimicrobials at drying-off, with a relatively small impact on cow health.HighlightsFirst observational study in of Italian dairy herds on the application of a selective dry-cow therapy protocol based on SCC.The study showed as a reduction of about 50% in antimicrobial usage at drying off can be achieved.Management and cow factors affect the likelihood of a cure of a new intramammary infection across the dry period. First observational study in of Italian dairy herds on the application of a selective dry-cow therapy protocol based on SCC. The study showed as a reduction of about 50% in antimicrobial usage at drying off can be achieved. Management and cow factors affect the likelihood of a cure of a new intramammary infection across the dry period.

选择性干奶疗法（Selective Dry Cow Therapy, SDCT）是奶牛场减少抗生素使用的推荐措施之一，但该疗法或对奶牛群产生负面影响，波及牛奶产量与品质。本观察性研究旨在评估一项基于体细胞计数（Somatic Cell Count, SCC）的选择性干奶疗法方案的实施效果：该方案仅对干奶前最后一次个体牛奶检测中体细胞计数超标的奶牛进行治疗，其中初产奶牛的阈值为＞100000个细胞/mL，经产奶牛为＞200000个细胞/mL，并分析该方案对乳房感染状态的影响。本研究同时评估了奶牛自身与饲养管理因素与干奶期内感染治愈或新发乳房内感染（Intramammary Infection, IMI）概率的相关性。

本研究共纳入516头奶牛（共计2064个乳区），其中仅53%的奶牛接受了抗生素治疗。干奶前，通过两份连续采集的奶样检测，999个乳区（占比49.1%）呈细菌学阴性；产后，细菌学阴性乳区数量为1004个，占比49.3%。干奶期内感染治愈概率与胎次、干奶时长及乳头密封剂使用情况显著相关；而干奶期新发乳房内感染概率则与本研究纳入的全部风险因素相关，包括胎次、干奶时长、乳头密封剂使用情况、干奶时的感染状态以及所用长效抗生素的类型。

在田间条件下应用本研究提出的选择性干奶疗法方案，被证实具备可行性，可大幅降低干奶阶段的抗菌药物使用量，且对奶牛健康的影响相对有限。

研究亮点：本研究是意大利奶牛场中首个基于体细胞计数开展选择性干奶疗法应用的观察性研究。本研究证实，干奶阶段的抗菌药物使用量可降低约50%。饲养管理与奶牛自身因素会影响干奶期内感染治愈或新发乳房内感染的概率。本研究是意大利奶牛场中首个基于体细胞计数开展选择性干奶疗法应用的观察性研究。本研究证实，干奶阶段的抗菌药物使用量可降低约50%。饲养管理与奶牛自身因素会影响干奶期内感染治愈或新发乳房内感染的概率。