Subclinical mastitis is a common intramammary disease in sheep production systems. Expenses associated with compromised animal performance, therapeutic interventions, and decreased ewe longevity make efforts to minimize its prevalence worthwhile. The objectives of this study were to (i) quantify the prevalence of subclinical mastitis throughout lactation, (ii) evaluate the impact of bedding treatments on subclinical mastitis during early lactation, (iii) evaluate the efficacy of prophylaxis and feed restriction during weaning on subclinical mastitis cure rates, (iv) and identify levels and types of antimicrobial resistance in milk-derived bacteria. Ewe milk samples were collected at d 1, 2, and 28 post-partum, weaning, and 3-d post-weaning for bacterial identification via culture-based methods. Staphylococcus spp. and Streptococcus spp. isolates were subjected to in vitro antimicrobial susceptibility testing. The overall prevalence of subclinical mastitis defined by culture growth ranged between 22 and 66% and differences were observed between post-weaning and d 1 and 28 milk samples. Commonly isolated bacteria include coagulase-negative staphylococci (CoNS; 59%), Bacillus spp. (35%), Mannheimia haemolytica (10%), Staphylococcus aureus (8%), Streptococcus spp. (5%), and Corynebacterium spp. (5%). Early milk samples (d 1 and 2) were compared between jug bedding treatment: jugs were recently vacated, cleaned, and dusted with barn lime before adding fresh straw (CLEAN) or jugs were previously vacated and fresh straw was added atop soiled bedding (SOILED). Jug bedding treatment did not affect the prevalence of subclinical mastitis, though CoNS had greater sulfadimethoxine resistance in SOILED isolates than CLEAN isolates (P = 0.03). Three different weaning treatments were used: ewes were injected with penicillin at weaning (PENN), ewes had restricted feed access 48 h prior to and 72 h post-weaning (FAST), or a combination of these treatments (COMBO). Weaning treatment did not affect the prevalence of subclinical mastitis or cure rate from weaning to 3-d post-weaning, though all PENN and no FAST milk S. aureus isolates were resistant against tetracycline (P = 0.08). Subclinical mastitis prevalence tended to decrease from weaning to post-weaning (P = 0.08). These data show subclinical mastitis is common throughout lactation and the levels of antimicrobial resistance of bacteria isolated from ewe milk are generally low against commonly used antimicrobials.

中文翻译：

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哺乳早期和断奶期间管理策略对绵羊亚临床乳腺炎病原体和乳源性细菌分离株抗菌敏感性的影响


亚临床型乳腺炎是绵羊生产系统中常见的乳房内疾病。与动物性能受损、治疗干预和母羊寿命缩短相关的费用使得努力减少其患病率是值得的。本研究的目的是（i）量化整个哺乳期亚临床乳腺炎的患病率，（ii）评估哺乳早期垫料治疗对亚临床乳腺炎的影响，（iii）评估断奶期间预防和饲喂限制对亚临床乳腺炎的效果。乳腺炎治愈率，(iv) 并确定乳源细菌中抗菌药物耐药性的水平和类型。在产后第 1、2 和 28 天、断奶和断奶后 3 天收集母羊乳样品，通过基于培养的方法进行细菌鉴定。葡萄球菌属和链球菌属。对分离株进行体外药敏试验。由培养物生长定义的亚临床乳腺炎的总体患病率在 22% 至 66% 之间，并且在断奶后以及第 1 和第 28 天的牛奶样品之间观察到差异。常见分离的细菌包括凝固酶阴性葡萄球菌（CoNS；59%）、芽孢杆菌属。 (35%)、溶血曼海姆菌 (10%)、金黄色葡萄球菌 (8%)、链球菌属。 (5%) 和棒状杆菌属。 (5%)。比较罐垫料处理之间的早期牛奶样品（第 1 天和第 2 天）：罐子最近被腾空、清洁，并在添加新鲜稻草之前撒上谷仓石灰（清洁），或者罐子之前被腾空，并在弄脏的垫料上添加新鲜稻草（脏污） ）。尽管 CoNS 在污染的分离株中比清洁的分离株具有更高的磺胺二甲氧嘧啶耐药性，但罐垫治疗并不影响亚临床乳腺炎的患病率 (P = 0.03)。 使用三种不同的断奶处理：断奶时给母羊注射青霉素（PENN），断奶前48小时和断奶后72小时限制母羊采食（FAST），或这些处理的组合（COMBO）。断奶治疗并不影响亚临床乳腺炎的患病率或从断奶到断奶后 3 d 的治愈率，尽管所有 PENN 菌株和无 FAST 牛奶金黄色葡萄球菌菌株均对四环素具有耐药性（P = 0.08）。从断奶到断奶后，亚临床乳腺炎患病率呈下降趋势（P = 0.08）。这些数据表明，亚临床乳腺炎在整个哺乳期很常见，并且从母羊奶中分离出的细菌对常用抗菌药物的耐药水平通常较低。