The objective of the study was to evaluate the utility of a Petrifilm-based on-farm culture system when used to make selective antimicrobial treatment decisions on low somatic cell count cows (<200,000 cells/mL) at drying off. A total of 729 cows from 16 commercial dairy herds with a low bulk tank somatic cell count (<250,000 cells/mL) were randomly assigned to receive either blanket dry cow therapy (DCT) or Petrifilm-based selective DCT. Cows belonging to the blanket DCT group were infused with a commercial dry cow antimicrobial product and an internal teat sealant (ITS) at drying off. Using composite milk samples collected on the day before drying off, cows in the selective DCT group were treated at drying off based on the results obtained by the Petrifilm on-farm culture system with DCT + ITS (Petrifilm culture positive), or ITS alone (Petrifilm culture negative). Quarters of all cows were sampled for standard laboratory bacteriology on the day before drying off, at 3 to 4d in milk (DIM), at 5 to 18 DIM, and from the first case of clinical mastitis occurring within 120 DIM. Multilevel logistic regression was used to assess the effect of study group (blanket or selective DCT) and resulting dry cow treatment (DCT + ITS, or ITS alone) on the risk of intramammary infection (IMI) at calving and the risk of a first case of clinical mastitis between calving and 120 DIM. According to univariable analysis, no difference was observed between study groups with respect to quarter-level cure risk and new IMI risk over the dry period. Likewise, the risk of IMI at calving and the risk of clinical mastitis in the first 120 DIM was not different between quarters belonging to cows in the blanket DCT group and quarters belonging to cows in the selective DCT group. The results of this study indicate that selective DCT based on results obtained by the Petrifilm on-farm culture system achieved the same level of success with respect to treatment and prevention of IMI over the dry period as blanket DCT and did not affect the risk of clinical mastitis in the first 120 d of the subsequent lactation.

This study evaluated matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-ToF MS) for the identification of bovine-associated coagulase-negative staphylococci (CNS), a heterogeneous group of different species. Additionally, we aimed to expand the MALDI-ToF MS database with new reference spectra as required to fill the gaps within the existing commercial spectral library. A total of 258 isolates of CNS were used in the study, covering 16 different CNS species. The majority of the isolates were previously identified by rpoB gene sequencing (n = 219), and the remainder were identified by sequencing of 16S rRNA, hsp60, or both rpoB and hsp60. The genotypic identification was considered the gold standard identification. All MALDI-ToF MS identifications were carried out using the direct transfer method. In a preliminary evaluation (n = 32 isolates; 2 of each species) with the existing commercial database, MALDI-ToF MS showed a typeability of 81% (26/32) and an accuracy of 96% (25/26). In the main evaluation (n = 226 isolates), MALDI-ToF MS with the existing commercial Biotyper (Bruker Daltonics Inc., Billerica, MA) database achieved a typeability of 92.0% (208/226) and an accuracy of 99.5% (207/208). Based on the assessment of the existing commercial database and prior knowledge of the species, a total of 13 custom reference spectra, covering 8 species, were created and added to the commercial database. Using the custom reference spectra expanded database, isolates were identified by MALDI-ToF MS with 100% typeability and 100% accuracy. Whereas the MALDI-ToF MS manufacturer's cutoff for species-level identification is 2.000, the reduction of the species level cutpoint to ≥1.700 improved the species-level identification rates (from 64 to 92% for the existing commercial database) when classifying CNS isolates. Overall, MALDI-ToF MS using the direct transfer method was shown to be a highly reliable tool for the identification of bovine-associated CNS.

Compared with blanket dry cow therapy (DCT), the selective antimicrobial treatment of cows based upon on-farm culture results has the potential to reduce the amount of antimicrobials used in dairy production. The objective of the current study was to determine the effect of a Petrifilm (3M Canada, London, Ontario) on-farm culture-based selective DCT program on milk yield and somatic cell count (SCC) in the following lactation. A total of 729 low-SCC (<200,000 cells/mL) cows from 16 commercial dairy herds with a low bulk tank SCC (<250,000 cells/mL) were randomly assigned to receive either blanket DCT or Petrifilm-based selective DCT. Cows belonging to the blanket DCT group were infused with a commercial DCT product and an internal teat sealant (ITS) at drying off. Using composite milk samples collected on the day before drying off, cows in the selective DCT group were treated at drying off based on the results obtained by the Petrifilm on-farm culture system with DCT and ITS (Petrifilm culture positive) or ITS alone (Petrifilm culture negative). Milk test-day records for the following lactation were obtained from Dairy Herd Improvement for all cows enrolled in the trial. Repeated measures linear mixed models were used to assess the effect of study group (blanket or selective DCT) on test-day milk production and natural logarithm of SCC over the first 180 d of the subsequent lactation. According to the final multivariable models, when low-SCC cows were selectively treated with DCT at drying off based on results obtained using the Petrifilm on-farm culture system, no effect on milk production (least squares means for blanket DCT = 39.3 kg vs. selective DCT = 39.0 kg) or natural logarithm of SCC (least squares means for blanket DCT = 3.95 vs. selective DCT = 3.97) was observed in the subsequent lactation when compared with cows receiving blanket DCT. The results of this study indicate that selective DCT based on results obtained by the Petrifilm on-farm culture system enabled a reduction in the use of DCT without negatively affecting milk production and milk quality.

The objective of this randomized controlled trial was to assess the efficacy of an on-farm culture system using Petrifilm (3M, London, ON, Canada) for targeted treatment decisions at the quarter level at dry-off and its effects on dry period intramammary infections (IMI) and udder health and milk production in the subsequent lactation. A total of 568 cows (2,247 quarters) from 9 dairy herds with bulk tank somatic cell count <250,000 cells/mL in Québec, Canada, were systematically enrolled and randomly allocated to 4 groups: 2 quarter-based selective (QSDCT) groups, using results of quarter-milk culture on Petrifilm, and 2 blanket dry cow therapy (BDCT) groups. The 2 QSDCT groups consisted of (1) antimicrobial to infected quarters and internal teat sealant (ITS) to healthy quarters (QS-DCT/ITS); and (2) antimicrobial and ITS to infected quarters and ITS to healthy quarters (QSDCT+ITS/ ITS). The 2 BDCT groups were (1) antimicrobial alone to all quarters (BDCT); and (2) antimicrobial and ITS to all quarters (BDCT+ITS). Quarter milk samples were collected at dry-off and after calving for routine bacteriological culture at the laboratory to monitor IMI; data on milk production, somatic cell count, and clinical mastitis recorded up to 120 d in milk were retrieved from health and DHI records. The probability of avoiding antimicrobial treatment in QSDCT groups was estimated at 48.3% (95% confidence interval: 35.7, 60.9). There was no significant difference between the 4 treatment groups regarding acquisition of new IMI (15.9, 13.2, 15.8, and 15.1% probability for BDCT, BDCT+ITS, QSDCT/ITS, and QSDCT+ITS/ITS, respectively) or persistence of existing IMI (3.2, 2.1, 3.4, and 2.7% probability, respectively) over the dry period. In the subsequent lactation, there was no dif-ference between groups regarding incidence of clinical mastitis (2.4, 3.7, 2.9, and 1.7% respectively for BDCT, BDCT+ITS, QSDCT/ITS, and QSDCT+ITS/ITS), mean milk somatic cell score (1.7, 2.0, 2.0, and 2.0 respectively), or mean daily milk production (43.8, 44.2, 43.2, and 42.6 kg/d, respectively) during the first 120 d in milk. In conclusion, QSDCT using the Petrifilm on-farm culture system to detect infected quarters at dry-off is an interesting option to decrease antibiotic use without any negative effects on udder health or milk production in the first 120 d of the subsequent lactation compared with BDCT.