Milk Culture Results in a Large Norwegian Survey—Effects of Season, Parity, Days in Milk, Resistance, and Clustering

Abstract

A nationwide random computerized assignment survey that included 3,538 sets of 4 quarter milk samples from 2,834 dairy cows was conducted during 2000. Every fifth cow from every 50th herd was randomly selected for sampling and culture during each quarter of the year. Milk culture results of pathogens known to be related to mastitis were recorded regardless of whether mastitis had been indicated by any inflammatory measure or not. Farmers were blinded to all test results to minimize any potential interventions that might be prompted by the results. The most prevalent isolate was Staphylococcus aureus, which was identified in 8.2% of the quarter milk samples. More than 15 colony-forming units/0.01 mL of Staph. aureus were found in 4.3% of the quarter milk samples, whereas 3.5% had only 1 to 3 colony-forming units/0.01 mL. Streptococcus dysgalactiae, coagulase-negative staphylococci (CNS), and Streptococcus uberis were isolated from 1.2, 3.3, and 0.4% of quarter milk samples, respectively. No isolates were found in 76.6% of the quarter milk samples tested. Among individual cows, 22.2% had an isolate of Staph. aureus in > or = 1 quarter. Only Strep. dysgalactiae exhibited a higher prevalence with increased parity. Prevalence of Staph. aureus decreased throughout days in milk, but prevalence of Strep. dysgalactiae increased. There was a strong seasonal effect; the highest prevalence of Strep. dysgalactiae and CNS was observed during April and May (late indoor season), and the highest prevalence of Staph. aureus and Strep. uberis was observed during June and July (the outdoor season). A substantial within-cow clustering effect was found for Strep. dysgalactiae, Staph. aureus, and CNS. Additionally, a within-herd effect was found for Strep. uberis, penicillin-resistant Staph. aureus, total Staph. aureus, and CNS. No within-county cluster effect was found. Lastly, both Staph. aureus and CNS exhibited a surprisingly high seasonal effect regarding the prevalence of resistance to penicillin G. Penicillin resistance of Staph. aureus was likely due to higher prevalence of Staph. aureus as a whole, but for CNS, there was also an additional increase caused by a higher proportional rate of penicillin resistance during the late indoor season.

Diagnosis of Intramammary Infections at Dry-off Based on Sampling Strategy, Epidemiology of Pathogens, and Agreement Beyond Chance

“…For minor pathogens, thresholds of 1,000 and 4,000 CFU/ml have been used to declare an IMI. 2,21 In the present study, using a cutoff of 1,000 CFU/ml for minor pathogens provided an almost perfect agreement 7 between the first and the second sample in DS (kappa 5 0.83, which was significantly higher than kappa 5 0.56 with a cutoff of 100 CFU/ml). This finding supports the use of higher cutoffs for these types of organisms.…”

“…Isolation of $100 CFU/ml of major contagious pathogens has been commonly used to diagnose IMI from quarter milk samples collected from cows with clinical 2,14 and subclinical mastitis. 21,30,32 However, some common mastitis pathogens can colonize teat skin and/or the teat canal without causing IMI 20 or can be environmental contaminants in milk. Therefore, isolation of .100 CFU/ml of milk may be required as an indication of a true IMI with these types of pathogens.…”

“…Therefore, isolation of .100 CFU/ml of milk may be required as an indication of a true IMI with these types of pathogens. When noncontagious major pathogens are considered, higher cutoffs for CFU/ml have been suggested and used as a requirement to diagnose IMI (e.g., $200 CFU/ml, 2 400 CFU/ml, 21 or 500 CFU/ml 23,26,27 ). The results of the current study agree with the suggested higher cutoffs, as the agreement for the major environmental pathogens between the first and the second sample was highest using a cutoff value of 1,000 CFU/ml.…”

Prevalence and herd-level risk factors for intramammary infection with coagulase-negative staphylococci in Dutch dairy herds

“…Although a causal relation 19 between these factors and prevalence of CNS is not proven and for some factors not even 20 likely, knowledge of the associations found may by helpful when approaching CNS problems 21 on dairy farms. 22 M a n u s c r i p t 6 selected. These samples were thawed at room temperature and then cultured again.…”

Herd level approach to high bulk milk somatic cell count problems in dairy cattle

“…Information about seasonality can be important too. For example, in the Netherlands and in Norway, a recurrent increase in BMSCC during the summer pasture season is likely due to S. uberis mastitis or, in Norway, S. aureus mastitis, whereas a similar increase in BMSCC during the winter housing season is more likely to be due to S. dysgalactiae mastitis (Barkema 1999;Osteras et al 2006;Olde Riekerink et al 2007).…”