McDougall S
Animal Health Centre, PO Box 21, Morrinsville, New Zealand.
N Z Vet J. 1999 Aug;47(4):143-9. doi: 10.1080/00480169.1999.36131.
To determine the prevalence of clinical mastitis in spring-calving dairy herds in the Waikato Region of New Zealand and to identify factors associated with variation in the prevalence of clinical mastitis between herds.
A total of 799 quarters from 595 dairy cows from 38 dairy herds were diagnosed by herd owners as having clinical mastitis between 8 July and 21 August 1997. Quarters diagnosed with clinical mastitis were sampled for bacterial culture and somatic cell count, and the presence of clots in the milk and the presence of udder oedema were assessed by a technician or veterinarian.
Clinical mastitis was diagnosed in an average (+/-s.e.m.) of 9.9% (+/-0.8%, range 0.9-21.4%) of calved cows within the herds. Bacteria were not cultured from an average of 12.4 % (+/- 2.0%, range 0.0-45.5%) of cows and 22.3% (+/- 2.4%, range 0.0-54.0%) of quarters diagnosed as having clinical mastitis. There were significant differences between herds in the proportion of cows diagnosed with mastitis and in the proportion of clinical mastitis cases from which bacteria were not cultured. A decreased prevalence of clinical mastitis (p<0.001) was associated with an increased percentage of the herd treated with dry cow antibiotics. An increased prevalence of clinical mastitis (p<0.0001) was associated with both an increased percentage of cows treated in the previous season with lactating cow antibiotics and an increased percentage of heifers in the herd. Herds that were fed supplements before or during lactation had a higher prevalence of clinical mastitis than herds that were not fed supplements (p<0.001). An increased proportion of quarters diagnosed with clinical mastitis that did not culture bacteria was associated with an increased prevalence of clinical mastitis (p<0.001). The proportion of quarters that the technician or veterinarian found with evidence of clinical mastitis (i.e. a somatic cell count >500,000 cells/ml and the presence of either clots or udder oedema) within a herd was inversely related to the proportion of quarters within a herd from which no bacteria were isolated.
There was a large variation in the prevalence of clinical mastitis and in the proportion of clinical quarters from which no bacteria were grown between herds. Management factors such as the use of dry cow therapy, feeding regimes and heifer replacement rates all affected the prevalence of clinical mastitis. Herd owners appear to differ in the sensitivity and specificity of their diagnosis of clinical mastitis, with bacteria not isolated from up to 50% of quarters diagnosed with clinical mastitis in some herds. Improvements in the specificity of herd owner diagnosis of clinical mastitis may reduce the use of antibiotics for mastitis during lactation and hence may reduce the risk of antibiotic contamination of milk supplied for human consumption.
确定新西兰怀卡托地区春季产犊奶牛群临床型乳腺炎的患病率，并找出与不同牛群间临床型乳腺炎患病率差异相关的因素。
1997年7月8日至8月21日期间，38个奶牛群的595头奶牛的799个乳腺区被畜主诊断为患有临床型乳腺炎。对诊断为临床型乳腺炎的乳腺区进行细菌培养和体细胞计数采样，由技术人员或兽医评估牛奶中凝块的存在情况以及乳房水肿情况。
各牛群中平均（±标准误）有9.9%（±0.8%，范围0.9 - 21.4%）的产犊母牛被诊断为临床型乳腺炎。平均有12.4%（±2.0%，范围0.0 - 45.5%）的奶牛以及22.3%（±2.4%，范围0.0 - 54.0%）被诊断为临床型乳腺炎的乳腺区未培养出细菌。不同牛群间被诊断为乳腺炎的奶牛比例以及未培养出细菌的临床型乳腺炎病例比例存在显著差异。临床型乳腺炎患病率降低（p<0.001）与干奶牛抗生素治疗牛群比例增加有关。临床型乳腺炎患病率增加（p<0.0001）与上一季接受泌乳期奶牛抗生素治疗的奶牛比例增加以及牛群中后备母牛比例增加有关。在泌乳期之前或期间饲喂补充饲料的牛群，其临床型乳腺炎患病率高于未饲喂补充饲料的牛群（p<0.001）。被诊断为临床型乳腺炎但未培养出细菌的乳腺区比例增加与临床型乳腺炎患病率增加有关（p<0.001）。技术人员或兽医在一个牛群中发现有临床型乳腺炎证据（即体细胞计数>500,000个细胞/毫升且存在凝块或乳房水肿）的乳腺区比例与该牛群中未分离出细菌的乳腺区比例呈负相关。
不同牛群间临床型乳腺炎患病率以及未培养出细菌的临床型乳腺区比例存在很大差异。干奶牛治疗的使用、饲养方式和后备母牛替换率等管理因素均会影响临床型乳腺炎的患病率。畜主对临床型乳腺炎的诊断敏感性和特异性似乎存在差异，在一些牛群中，高达50%被诊断为临床型乳腺炎的乳腺区未分离出细菌。提高畜主对临床型乳腺炎诊断的特异性可能会减少泌乳期乳腺炎抗生素的使用，从而降低供人类消费的牛奶受到抗生素污染的风险。
