Subclinical mastitis, the asymptomatic inflammation of the udder often caused by bacterial infection, is an important economic and welfare concern in meat-producing flocks. We conducted a longitudinal observational study to: (1) characterize the etiology, prevalence, incidence, and persistence of intramammary infections during the first 8 weeks of lactation, and (2) to investigate the potential risk factors of lactation stage, parity, and the number of lambs reared. Duplicate milk samples (n=592) were collected aseptically from each udder half of 37 clinically healthy ewes (9 Hampshire, 22 Polypay, and 6 Targhee) weekly for their first 8 weeks of lactation. A sample was considered a true infection if at least 100 CFU/mL of a bacterial species were isolated. Out of a total of 560 non-contaminated duplicate udder half samples, 186 (33.2%) were infected. The prevalence of subclinical mastitis in the first week of lactation was 26.0% at the udder half level and increased over lactation to 47.1% by 8 weeks. Over the course of lactation, 34 of 37 (91.9%) ewes had an intramammary infection in at least one udder half. The most common bacteria isolated were non-aureus Staphylococci (72.1%), Staphylococcus aureus (7.5%), and Mannheimia haemolytica (5.9%). The weekly incidence rate of new infections was 18.0 ± 10.2% (mean ± SD). Infections lasted 2.1 ± 2.1 weeks, with 9.0% present the full 8 weeks of observation. Spontaneous cures occurred in 36.0% of infection bouts but varied from 0 to 100% depending on the pathogen. The probability of subclinical mastitis infection increased as lactation progressed for ewes rearing single or multiple lambs and for ewes in their first or second parity, but not for ewes in later parities. In conclusion, intramammary infections in this flock were prevalent across lactation, parities, and litter sizes, and varied in their duration and spontaneous cure rate. Improved knowledge of the etiological agents and risk factors involved in subclinical mastitis is important in developing effective control measures in meat-producing flocks.

中文翻译：

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肉用羊群亚临床乳腺炎的病因、持续性和危险因素


亚临床乳腺炎，即通常由细菌感染引起的乳房无症状炎症，是肉用鸡群的一个重要经济和福利问题。我们进行了一项纵向观察研究，以： （1） 描述泌乳前 8 周乳腺感染的病因、患病率、发生率和持续性，以及 （2） 调查泌乳期、胎次和饲养羔羊数量的潜在危险因素。在泌乳的前 8 周，每周从 37 只临床健康的母羊 （9 只 Hampshire、22 只 Polypay 和 6 只 Targhee） 的每个乳房的一半乳房无菌收集重复的牛奶样本 （n=592）。如果分离出至少 100 CFU/mL 的细菌种类，则认为样本为真正感染。在总共 560 个未受污染的重复乳房半样本中，186 个 （33.2%） 被感染。泌乳期第一周乳房半部亚临床乳腺炎的患病率为 26.0%，泌乳期到 8 周时增加到 47.1%。在泌乳过程中，37 只母羊中有 34 只 （91.9%） 至少有一个乳房半部发生乳腺内感染。分离出的最常见细菌是非金黄色葡萄球菌 （72.1%） 、 金黄色葡萄球菌 （7.5%） 和溶血曼海姆菌 （5.9%）。新感染的每周发病率为 18.0 ± 10.2% （平均 ± SD）。感染持续 2.1 ± 2.1 周，其中 9.0% 的患者在观察 8 周后出现。36.0% 的感染发作发生自发治愈，但根据病原体的不同，自 发治愈率从 0% 到 100% 不等。对于饲养单只或多只羔羊的母羊以及第一胎或第二胎的母羊，亚临床乳腺炎感染的可能性随着泌乳时间的进行而增加，但对于较晚胎次的母羊则没有。 总之，该鸡群的乳腺内感染在泌乳期、胎次和窝产仔数中普遍存在，并且持续时间和自发治愈率各不相同。提高对亚临床乳腺炎相关病原体和危险因素的了解对于在肉鸡群中制定有效的控制措施非常重要。