Differences in Sensitivity of Milk Fermentation to Lactating Cow and Dry Cow Intra-mammary Antimicrobial Agents

Abstract

Antimicrobial agents for treatment of mastitis in dairy cows may result in drug residues in milk, suppressing production of fermented dairy products. The objective of this study was to compare the effects of lactating cow and dry cow intra-mammary antimicrobial preparations on fermentation of milk. Samples of ultra-high temperature-treated milk + starter culture (Lactococcus lactis subsp. lactis), were prepared. Using serial double dilution, erythromycin-trimethoprim lactating cow formula was added to five samples at 62.5-1000 mg/L and cloxacillin benzathine dry cow preparation to another five at 75-1200mg/L. A negative control with neither starter culture nor antimicrobial agent, and a positive control with starter culture but no antimicrobial agent were included. All samples were incubated at 30° C for two days and osmolarity (mOsmoles/L) monitored by a cryoscopic osmometer. From a starting value of 301±1.72 for fresh milk, osmolarity of non-inoculated milk did not rise beyond 314±7.07. Maximum osmolarity of inoculated milk attained in the presence of erythromycin-trimethoprim was 328±0.97, in contrast to 507±35.53 in the presence of cloxacillin benzathine. Hence hydrophilic lactating cow antimicrobial formulas exert a highly significant inhibitory effect on milk fermentation compared to hydrophobic dry cow antimicrobial preparations.