Efficacy of two long-acting intramammary antimicrobials for curing subclinical mastitis due to non-aureus staphylococci in dairy goats

Non-aureus staphylococci are the most prevalent cause of subclinical mastitis in dairy goats. The goals of this study were to describe the prevalence of subclinical mastitis pathogens on commercial goat dairies in the United States and evaluate the efficacy of intramammary antimicrobials for curing subclinical mastitis caused by NAS.¹

Does enrolled in this study were residents of one of three commercial dairies in either IA, WI, or CA. Enrollment criteria included no evidence of clinical mastitis, two functional udder halves, no antimicrobial or anti-inflammatory treatment within 30 days prior to dry-off, and an expected dry period between 30 and 90 days. All eligible does had aseptic milk samples collected for aerobic culture one week prior to scheduled dry-off. Pathogens were isolated and identified using standard laboratory techniques and confirmed using Matrix Assisted Laser Desorption Ionization-Time of Flight. Halves that cultured positive for NAS were randomly assigned to one of three treatment groups: 500 mg CLOX² (Orbenin DC, Merck & Co., Rahway, NJ), 300 mg CEPH³ (ToMORROW, Boehringer Ingelheim Vetmedica, Duluth, GA), or NT.⁴ If the contralateral half also cultured positive, it was assigned the same treatment group as the other half. Contralateral halves that cultured negative were enrolled as NC⁵ and no therapy was administered. Each enrolled doe had post-kidding aseptic milk samples collected for aerobic culture within 7 days of parturition. Cured infection risk was used to evaluate efficacy of each treatment.

Data analysis was completed using publicly available statistical software. Of all halves sampled prior to dry-off, 38.6 % had subclinical infection with NAS at dry-off. Across all farms 85.4 % of CEPH treated halves experienced a cure while 81.4 % of CLOX treated halves cured during the dry period and 54.1 % of NT halves. Both antimicrobial treatments were significantly more effective for curing infections than non-treatment (P < 0.001). Given the high prevalence of subclinical mastitis due to NAS at dry-off and the improved cure rates with administration of a long-acting intramammary antimicrobials compared with non-treatment, selective dry therapy can be an effective management strategy for commercial goat dairies in the US.