Patterns of mycoplasma shedding in the milk of dairy cows with intramammary mycoplasma infection

Abstract

Objective - To determine patterns of mycoplasma shedding in the milk of dairy cows with intramammary mycoplasma infection. Design - Prospective clinical trial. Animals-10 Holstein cows with intramammary mycoplasma infection. Procedure - Milk samples were collected from each cow daily for 28 days and plated on mycoplasma agar to evaluate shedding patterns. To determine whether enrichment improved recovery of organisms, some samples were also inoculated in mycoplasma enrichment medium and incubated for 4 days prior to plating. Somatic cell count (SCC) was determined in samples collected weekly. Results - Mycoplasma organisms were not isolated from 81 of 280 (29%) composite milk samples, but > 106 colonies/mL were obtained from 151 (54%). Similarly, mycoplasma organisms were not isolated from 433 of 1,008 (43%) quarter milk samples, but > 106 colonies/mL were obtained from 392 (39%). For 71 of 104 (68%) samples, mycoplasma organisms were isolated both following direct plating and following enrichment; for 24 of 104 (23%), mycoplasma organisms were isolated only following enrichment; and for 9 of 104 (9%), mycoplasma organisms were isolated only after direct plating. There was a linear correlation between logarithm of the SCC and logarithm of the number of colony-forming units of mycoplasma per milliliter of milk for composite and quarter milk samples. Conclusions and Clinical Relevance - Shedding of organisms was inconsistent in dairy cows with intramammary mycoplasma infection, increasing the risk of misdiagnosis if multiple milk samples are not tested.