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Negatively controlled, randomized clinical trial comparing label intramammary use of amoxicillin to ceftiofur hydrochloride for treatment of bovine clinical mastitis caused by Gram-positive pathogens
Tomazi, T.; Sumnicht, M.; Tomazi, A...
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Objectives: This negatively controlled field trial aimed to compare clinical, microbiological and performance outcomes of label use of a narrow spectrum antimicrobial (amoxicillin) with a wide spectrum antimicrobial (ceftiofur hydrochloride) for treatment of non-severe clinical mastitis (CM) caused by Gram-positive bacteria.
Material and methods: After microbiological culture results, lactating dairy cows with non-severe CM (without systemic symptoms) caused by Gram-positive bacteria were as- signed to two protocols: AMOX - three infusions with 62.5 mg of amoxicillin (Amoxi-Mast®, Merck Animal Health) performed ~12 hours apart; CEFT - five infusions with 125 mg of ceftiofur hydrochloride (Spectramast®, Zoetis) performed ~24 hours apart; NEG-CTR – quarters assigned to this group did not receive any interventions until five days after diagnosis. Before the onset of the study a randomized list was created to pre-assign all pregnant animals to one of treatment groups; approximately 90% of cows were assigned to one of antibiotic treatment groups (~45% in each protocol) and 10% to the negative control.
Duplicate milk samples taken before treatment (day 0) and on days 3, 5, 8 and 14 ± 3 after enrollment for analysis of milk composition, somatic cell count (SCC), total bacterial count (TBC) and next-generation sequencing of 16S rRNA gene and quantitative PCR (qPCR). Multivariate logistic regression models were created to evaluate dichotomized outcomes such as clinical cure (CC) and bacteriological cure (BC) at 14 ± 3 days after enrollment and quarter-level CM recurrence by the same species up to 90 days after treatment. Repeated-measures analysis of ANOVA was conducted to analyze the effect of treatment on milk production, SCC, composition, TBC, bac- terial relative abundance (RA; based on microbiota) and 16S rRNA gene copy numbers (based on qPCR).
Results: A total of 477 quarter-cases of CM were evaluated: 198 assigned to AMOX, 223 to CEFT and 56 to NEG- CTR. The most frequent isolated species were Streptococcus uberis (60.6%), Strep. dysgalactiae (19.3%), Streptococcus spp. (8.4%) and non-aureus staphylococci (6.1%). The overall CC (based on least square means) was 84.1% for AMOX and 89.0% for CEFT, and no significant statistical difference (P=0.15) was observed between groups. Likewise, no difference (P=0.10) between groups was observed on the evaluation of BC (AMOX = 58.2%; CEFT = 66.4%). Moreover, we found no statistical differences (P>0.05) between treatments when comparing CC and BC according to the mastitis-causing species (i.e., Strep. uberis, Strep. dysgalactiae or combination of other pathogens).
Compared to antibiotic treated groups, quarters assigned to NEG-CTL had higher CFU, 16S rRNA gene copy numbers, and Streptococcus RA until day five after enrollment. Moreover, milk samples from NEG-CTL cows had lower fat and lactose contents, and higher total protein than antibiotic-treated cows up to the third test day after enrollment. A substantial reduction of bacterial load (CFU and qPCR) and Streptococcus RA was found for quarters receiving antibiotic therapy. Quarters treated with AMOX had higher CFU on days 5, 8 and 14 after enrollment compared to CEFT. In addition, the relative abundance of Strep. uberis was higher on day 14 after enrollment for AMOX-treated quarters than for those assigned to CEFT group, which may be related to the duration of treatment.
Linear score of SCC (LSSCC) was higher for AMOX-treated cows than for those treated with CEFT in the first test day after CM, but no differences were observed in the second and third test days following CM. Higher milk production was observed for cows assigned to AMOX group compared with CEFT-treated cows until the third test day after enrollment. No significant differences between groups (P=0.92) were found on CM recurrence (9.0% for CEFT; 9.3% for AMOX), and on survival of cows in the herd after treatment (P=0.51).
Conclusion: Two-day protocol with three intramammary infusions of amoxicillin (narrow spectrum antimicrobial) had similar CC and BC than five administrations (once a day) with ceftiofur hydrochloride (wide spectrum), and no difference was observed on the risk of CM recurrence and cow survival. However, quarters treated with 5-day ceftiofur protocol had higher reduction of milk CFU than quarters treated with amoxicillin up to 14 days after treatment. Antibiotic use remains an indispensable strategy for treatment of Gram-positive bacteria, since untreated quarters remained with high CFU, gene copy numbers and Streptococcus spp. RA than quarters receiving any of the antimicrobial protocols.
Keywords: Treatment of clinical mastitis, dairy cows, microbiome, Gram-positive mastitis pathogens.
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About
Affiliation of the authors at the time of publication
Department of Population Medicine and Diagnostic Sciences, Cornell University, Ithaca, United States;
Global Ruminants, MSD Animal Health, Boxmeer, Netherlands;
Merck Animal Health, De Soto, United States.
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