Mastitis is the most frequent reason for antibiotic use in New Zealand dairy cattle and technologies reducing and targeting this use contribute to responsible product stewardship. Rapid identification of pathogen and antibiotic susceptibility facilitate targeted treatment but currently involve a minimum 24 h delay. Studies from confinement systems where Gram-negative organisms are responsible for a significant proportion of mastitis, indicate selective treatment can reduce antibiotic use without reducing clinical or bacteriological cure. However, in New Zealand's seasonal, pastoral dairy system, mastitis is dominated by Gram-positive organisms and if treatment is deferred, it is vital both short- and long-term clinical health outcomes are not compromised. Mastatest® is a diagnostic system for bovine mastitis indicating the pathogen and its antibiotic sensitivity within 24 h of sampling. This study focused on evaluating this system's ability to control antibiotic usage whilst achieving equivalent bacteriological and clinical cure rates alongside long term individual somatic cell count (ISCC) outcomes as conventional treatment choices. Mild to moderate mastitis cases in the 100 days after calving in 6467 cows from 7 farms were milk sampled and randomly allocated to a positive control group non-selective treatment or a culture-based treatment. All milk samples were processed using Mastatest®. For the positive control, the quarter was treated immediately with 3 treatments of procaine penicillin every 12 h. For the selective treatment group, treatment was delayed for 24 h and then informed by pathogen and antibiotic sensitivity from the Mastatest® result. Gram-negative and no-growth quarters were untreated. Gram-positive quarters were treated with the antibiotic for which the lowest in vitro antimicrobial sensitivity was reported. Re-sampling was carried out from affected quarter(s) approximately 21 days after initial diagnosis and cultured for bacterial identification. Clinical recurrence within 60 days and ISCC data was recorded at herd tests over the duration of the lactation. Antimicrobial usage and days of milk withhold pending clearance of antibiotic residues were also noted. There was no difference in bacteriological or clinical cure rate between the two treatment groups. Final herd test ISCC and days of milk withhold from supply did not differ between groups. Antibiotic usage was 24 % less (95 % predictive interval = 12-47 %) in the selective group. This study suggests that on farm decisions about deferred treatment of mastitis using Mastatest® to identify the intramammary pathogen can reduce the antimicrobial usage with no loss in bacterial or clinical cure and with no effect on ISCC over the lactation.

中文翻译：

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选择性和延期治疗7个新西兰奶牛场的临床乳腺炎。

乳腺炎是新西兰奶牛使用抗生素的最常见原因，减少和针对这种使用的技术有助于负责任的产品管理。快速鉴定病原体和抗生素敏感性有助于靶向治疗，但目前至少要延迟24小时。限制系统的研究表明，革兰氏阴性菌在很大程度上导致了乳腺炎，而选择性治疗可以减少抗生素的使用而不会降低临床或细菌学治愈率。但是，在新西兰的季节性牧区奶业体系中，乳腺炎主要由革兰氏阳性菌所致，如果推迟治疗，短期和长期的临床健康状况都不会受到损害。Mastatest®是牛乳腺炎的诊断系统，可在采样后的24小时内指示病原体及其对抗生素的敏感性。这项研究的重点是评估该系统控制抗生素使用的能力，同时获得与常规治疗选择相同的细菌学和临床治愈率以及长期的个体体细胞计数（ISCC）结果。在产犊后100天内，对来自7个农场的6467头母牛的轻至中度乳腺炎病例进行牛奶采样，并随机分配至阳性对照组的非选择性治疗或基于培养的治疗。使用Mastatest®处理所有牛奶样品。对于阳性对照，每12小时立即用3种普鲁卡因青霉素治疗四分之一。对于选择性治疗组，治疗延迟了24小时，然后从Mastatest®结果中得知病原体和抗生素敏感性。革兰氏阴性和无生长的四分之一未经治疗。革兰氏阳性四分之一用据报道其体外抗菌敏感性最低的抗生素处理。初步诊断后约21天，从受影响的一个或多个季度进行重新采样，并进行培养以鉴定细菌。在泌乳期间，在畜群测试中记录60天内的临床复发和ISCC数据。还指出了抗菌剂的使用以及在等待清除抗生素残留之前停奶的天数。两个治疗组之间的细菌学或临床治愈率无差异。两组之间的最终牛群测试ISCC和停奶天数没有差异。选择性组的抗生素使用量减少了24％（95％的预测间隔= 12-47％）。这项研究表明，根据农场决定使用Mastatest®鉴定乳内病原体来延迟治疗乳腺炎，可以减少抗菌药物的使用，而不会造成细菌或临床治愈的损失，并且不会影响哺乳期的ISCC。