Interpretive Summary: Effects of management strategies during early lactation and weaning on etiological agents of ovine subclinical mastitis and antimicrobial susceptibility of milk-derived bacterial isolates

By: Ryan M Knuth, Kelly L Woodruff, Gwendolynn L Hummel, Jordan D Williams, Kathleen J Austin, Whitney C Stewart, Hannah C Cunningham-Hollinger, Bledar Bisha

Subclinical mastitis is a common intramammary disease in livestock. Expenses associated with compromised animal performance, therapeutic interventions, and decreased ewe longevity make minimizing its prevalence worthwhile. The objectives of this study were to quantify the prevalence of subclinical mastitis, evaluate the impact of bedding treatments on subclinical mastitis, evaluate the efficacy of weaning treatments, and identify levels of antimicrobial resistance in milk-derived bacteria. The overall prevalence of subclinical mastitis was 45%. Common bacteria included coagulase-negative staphylococci (CoNS), Bacillus spp., Mannheimia haemolytica, Staphylococcus aureus, Corynebacterium spp., and Streptococcus spp. Early lactation milk samples were compared between jug bedding treatments: jugs were cleaned before adding fresh straw (CLEAN) or jugs had fresh straw added atop soiled bedding (SOILED). Jug bedding treatment did not affect the prevalence of subclinical mastitis, though did affect CoNS resistance to sulfadimethoxine. Three different weaning treatments were used: ewes were administered penicillin at weaning, ewes had restricted feed access at weaning, or a combination of the two treatments. Weaning treatment did not affect the prevalence of subclinical mastitis, though subclinical mastitis prevalence decreased post-weaning. Our data show that subclinical mastitis is generally prevalent throughout lactation, and the levels of antimicrobial resistance of bacteria isolated from ewe milk are generally low.

Read the full article on the Journal of Animal Science.