Niemi R E, Hovinen M, Rajala-Schultz P J
Department of Production Animal Medicine, Faculty of Veterinary Medicine, University of Helsinki, Paroninkuja 20, 04920 Saarentaus, Finland.
Department of Production Animal Medicine, Faculty of Veterinary Medicine, University of Helsinki, Paroninkuja 20, 04920 Saarentaus, Finland.
J Dairy Sci. 2025 Feb;108(2):1914-1929. doi: 10.3168/jds.2024-25287. Epub 2024 Nov 8.
Intramammary antibiotic dry cow therapy (DCT) at the end of lactation is a key measure in the management and control of bovine mastitis. Currently, livestock production is under pressure to reduce antibiotic consumption, emphasizing the need to avoid medicating all cows at dry-off, and instead treat only infected cows. The study objective was to evaluate IMI cure risk, new IMI risk, and postcalving IMI risk between DCT-treated and untreated quarters over the dry period. The sample totaled 269 cows from 12 Finnish automatic milking system herds entering the dry period between 2019 and 2021. Cows eligible for the study had a final DHI test-day SCC ≥100,000 cells/mL and had no clinical signs of mastitis. Based on odd or even identification numbers, cows with an SCC between 100,000 and 250,000 cells/mL were sequentially assigned to either receive DCT at dry-off (DCT100-250) or remain untreated (NoDCT100-250). All cows with an SCC >250,000 cells/mL received DCT (DCT>250). No quarters received teat sealants. Farmers collected aseptic quarter milk samples for microbiological quantitative real-time PCR analysis 0 to 4 d before dry-off and 0 to 4 d after calving. The outcome of the statistical model was the odds of a quarter having an IMI at freshening 0 to 4 d after calving. The statistical tool was a generalized linear mixed-effects model with logit link function and 2-level random intercepts, cows nested within herds. Quarter-level IMI prevalence at dry-off was 17.6% (45/256) for NoDCT100-250, 22.2% (83/374) for DCT100-250, and 32.0% (132/413) for DCT>250. Quarter-level IMI prevalence at freshening was 36.2% (84/232) for NoDCT100-250, 13.6% (50/369) for DCT100-250, and 11.6% (46/397) for DCT>250. The untreated quarters in the NoDCT100-250 group had a 1.1 times higher risk of failing to cure over the dry period than the treated quarters in the DCT100-250 group (unadjusted risk ratio [RR] 1.10, 95% CI 0.94-1.28) and a 1.2 times higher risk than the treated quarters in the DCT>250 group (unadjusted RR 1.15, 95% CI 1.00-1.33). The untreated quarters in the NoDCT100-250 group had a 1.5 times higher risk of having a new IMI over the dry period than did the treated quarters in the DCT100-250 group (unadjusted RR 1.48, 95% CI 1.35-1.63) and a 1.4 times higher risk than the treated quarters in the DCT>250 group (unadjusted RR 1.35, 95% CI 1.23-1.49). The principal cause of new IMI was NAS, followed by Streptococcus dysgalactiae. Quarters in the NoDCT100-250 group had 6.6 times higher odds for having an IMI at freshening than did quarters in the DCT100-250 group (95% CI 3.52-12.21). According to our findings within the framework of this experiment, selectively DCT-treated cows with an SCC between 100,000 and 250,000 cells/mL at dry-off demonstrated that, although the group-specific cure risks over the dry period were high, untreated quarters had a higher risk of acquiring a new IMI over the dry period than did treated quarters, highlighting the effectiveness of DCT in reducing IMI risks. The prophylactic use of antibiotics, however, is not recommended, and in some countries is even prohibited.
泌乳期末的乳房内抗生素干奶疗法（DCT）是奶牛乳腺炎管理与控制的关键措施。当前，畜牧生产面临着减少抗生素使用量的压力，这凸显了避免在干奶期对所有奶牛用药、而仅对感染奶牛进行治疗的必要性。本研究的目的是评估干奶期接受DCT治疗和未接受治疗的乳腺在隐性乳房炎治愈风险、新发性隐性乳房炎风险以及产犊后隐性乳房炎风险方面的差异。样本包括来自芬兰12个自动挤奶系统牛群的269头奶牛，这些奶牛在2019年至2021年期间进入干奶期。符合研究条件的奶牛在最后一次DHI检测日的体细胞计数（SCC）≥100,000个/毫升，且无乳腺炎临床症状。根据奇偶识别号，将SCC在100,000至250,000个/毫升之间的奶牛依次分配为在干奶期接受DCT治疗（DCT100 - 250）或不接受治疗（NoDCT100 - 250）。所有SCC>250,000个/毫升的奶牛均接受DCT治疗（DCT>250）。所有乳腺均未使用乳头封闭剂。奶农在干奶前0至4天和产犊后0至4天采集无菌乳腺牛奶样本，用于微生物定量实时PCR分析。统计模型的结果是产犊后0至4天乳腺发生隐性乳房炎的几率。统计工具是一个广义线性混合效应模型，具有logit连接函数和两级随机截距，奶牛嵌套在牛群中。NoDCT100 - 250组干奶期乳腺水平的隐性乳房炎患病率为17.6%（45/256），DCT100 - 250组为22.2%（83/374），DCT>250组为32.0%（132/413）。产犊时乳腺水平的隐性乳房炎患病率，NoDCT100 - 250组为36.2%（84/232），DCT100 - 250组为13.6%（50/369），DCT>250组为11.6%（46/397）。NoDCT100 - 250组中未接受治疗的乳腺在干奶期未能治愈的风险比DCT100 - 250组中接受治疗的乳腺高1.1倍（未调整风险比[RR] 1.10，95%置信区间0.94 - 1.28），比DCT>250组中接受治疗的乳腺高1.2倍（未调整RR 1.15，95%置信区间1.00 - 1.33）。NoDCT100 - 250组中未接受治疗的乳腺在干奶期发生新发性隐性乳房炎的风险比DCT100 - 250组中接受治疗的乳腺高1.5倍（未调整RR 1.48，95%置信区间1.35 - 1.63），比DCT>250组中接受治疗的乳腺高1.4倍（未调整RR 1.35，95%置信区间1.23 - 1.49）。新发性隐性乳房炎的主要病因是无乳链球菌，其次是停乳链球菌。NoDCT100 - 250组的乳腺在产犊时发生隐性乳房炎的几率比DCT100 - 250组高6.6倍（95%置信区间3.52 - 12.21）。根据我们在本实验框架内的研究结果，在干奶期对SCC在100,000至250,000个/毫升之间的奶牛进行选择性DCT治疗表明，尽管各治疗组在干奶期的治愈风险较高，但未接受治疗的乳腺在干奶期发生新发性隐性乳房炎的风险高于接受治疗的乳腺，这突出了DCT在降低隐性乳房炎风险方面的有效性。然而，不建议预防性使用抗生素，在一些国家甚至被禁止。
