Department of Animal Science, University of Wyoming, Laramie, WY 82071, USA.
J Anim Sci. 2022 Jun 1;100(6). doi: 10.1093/jas/skac171.
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 1) quantify the prevalence of subclinical mastitis throughout lactation, 2) evaluate the impact of bedding treatments on subclinical mastitis during early lactation, 3) evaluate the efficacy of prophylaxis and feed restriction during weaning on subclinical mastitis cure rates, and 4) identify levels and types of antimicrobial resistance in milk-derived bacteria. Ewe milk samples were collected at days 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 days 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 (days 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 that 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.
隐性乳房炎是绵羊生产系统中常见的一种乳房内疾病。与动物生产性能下降、治疗干预以及母羊寿命缩短相关的费用使得降低其流行率变得非常有意义。本研究的目的是：1）定量评估泌乳期隐性乳房炎的流行率，2）评估早期泌乳期垫料处理对隐性乳房炎的影响，3）评估断奶时的预防和饲料限制对隐性乳房炎治愈率的影响，4）确定牛奶中分离细菌的耐药水平和类型。在产后第 1、2 和 28 天、断奶时和断奶后 3 天，通过基于培养的方法收集母羊奶样进行细菌鉴定。对金黄色葡萄球菌和链球菌分离株进行体外药敏试验。通过培养生长定义的隐性乳房炎总体流行率在 22%至 66%之间，且在断奶后和产后 1 天和 28 天的奶样之间存在差异。常见的分离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%）。将早期奶样（产后第 1 和 2 天）与 jug 垫料处理进行比较：jug 最近腾空，清洁并用厩石灰撒粉，然后添加新鲜稻草（CLEAN），或 jug 之前腾空，在污染垫料上添加新鲜稻草（SOILED）。jug 垫料处理不影响隐性乳房炎的流行率，但 SOILED 分离株中的 CoNS 对磺胺二甲氧嘧啶的耐药性大于 CLEAN 分离株（P = 0.03）。使用了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 小时限制母羊饲料（FAST），或这两种处理的组合（COMBO）。断奶处理不影响断奶至断奶后 3 天隐性乳房炎的流行率或治愈率，但 PENN 组的所有 S. aureus 分离株和 FAST 组无一株对四环素耐药（P = 0.08）。断奶后隐性乳房炎的流行率呈下降趋势（P = 0.08）。这些数据表明，隐性乳房炎在泌乳期很常见，且从母羊奶中分离出的细菌对常用抗生素的耐药水平通常较低。
