Department of Nutrition and Animal Production, School of Veterinary Medicine and Animal Sciences, University of São Paulo, São Paulo, Brazil.
J Dairy Sci. 2011 Sep;94(9):4406-12. doi: 10.3168/jds.2010-3776.
The objectives of this study were (1) to determine the sensitivity (Se) and specificity (Sp) of somatic cell count (SCC) thresholds to identify subclinical mastitis in Gyr cows caused by major and minor pathogens; (2) to study the effects of month of sampling, rear or front mammary quarters, herd, intramammary infection (IMI), and bacterial species on SCC at quarter level; and (3) to describe the prevalence of IMI in Gyr cows in commercial dairy herds. In total, 221 lactating Gyr cows from 3 commercial dairy farms were selected. Milk samples were collected from individual quarters once a month for 1 yr from all lactating cows for SCC and bacteriological analysis. Mammary quarters were considered the experimental units and the SCC results were log(10)-transformed. Four SCC thresholds (100, 200, 300 and 400 × 10(3) cells/mL) were used to determine Se and Sp to identify infected mammary quarters. The overall prevalence of IMI in quarter milk samples of Gyr cows was 49.8%, and the prevalence of minor pathogens was higher (31.9%) than that of major pathogens (17.8%). Quarter samples with microbial isolation presented higher SCC compared with negative samples. Sensitivity and Sp of selected SCC thresholds varied according to the group of pathogen (major and minor) involved in the IMI definition. Sensitivity increased and Sp decreased when mammary quarters with only major pathogens isolation were considered positive. The use of a single SCC analysis to classify quarters as uninfected or infected in Gyr cows may not be a useful test for this breed because Se and Sp of SCC at the studied thresholds were low. The occurrence of IMI and the bacterial species are the main factors responsible for SCC variation in mammary quarters of Gyr cows. Milk samples with major pathogens isolation elicited higher SCC than those with minor pathogens.
（1）确定体细胞计数（SCC）阈值的灵敏度（Se）和特异性（Sp），以识别由主要和次要病原体引起的 Gyr 奶牛亚临床乳腺炎；（2）研究采样月份、后乳区或前乳区、牛群、乳内感染（IMI）和细菌种类对乳区 SCC 的影响；（3）描述商业奶牛场 Gyr 奶牛的 IMI 流行情况。从 3 个商业奶牛场中选择了 221 头泌乳 Gyr 奶牛。从所有泌乳牛每月采集一次乳样，进行 SCC 和细菌分析，持续 1 年。乳区被视为实验单位，SCC 结果用对数（10）转换。使用 4 个 SCC 阈值（100、200、300 和 400×103 个细胞/mL）来确定识别感染乳区的 Se 和 Sp。Gyr 奶牛乳区 IMI 的总体流行率为 49.8%，次要病原体的流行率（31.9%）高于主要病原体（17.8%）。有微生物分离的乳区样本的 SCC 高于阴性样本。所选 SCC 阈值的灵敏度和 Sp 根据 IMI 定义中涉及的病原体（主要和次要）组而有所不同。当仅考虑主要病原体分离的乳区为阳性时，灵敏度增加，Sp 降低。在 Gyr 奶牛中，使用单一 SCC 分析将乳区分类为未感染或感染可能不是一种有用的测试，因为在研究的阈值下 SCC 的 Se 和 Sp 较低。IMI 的发生和细菌种类是 Gyr 奶牛乳区 SCC 变化的主要因素。有主要病原体分离的乳样的 SCC 高于有次要病原体分离的乳样。
