The main goal of dry cow therapy (DCT) is to cure existing intramammary infections (IMI) at dry off. Although several published studies have estimated the cure rate of IMI after DCT, variation among studies is great, which makes it difficult to conduct a proper economic evaluation of DCT. The objective of the present meta-analysis of existing peer-reviewed literature was to provide a summary quantification of quarter IMI cure based on DCT. A meta-analysis relative risk (RR) was calculated per intervention and pathogen group when at least 4 studies were available for analysis per comparison from the 22 selected studies, according to the selection criteria. Results of the meta-analysis were examined using publication bias tests. Blanket DCT with a 95% confidence interval (CI) provided a 1.78 (1.51 to 2.10) times higher calculated cure rate from quarter IMI during the dry period up to 21 d postcalving, compared with no DCT. The RR of cure was similar when treatment was conducted for Streptococcus spp. IMI quarters compared with Staphylococcus spp. IMI quarters. The pooled RR with the 95% CI were 1.83 (1.48 to 2.35) and 1.65 (1.38 to 1.96), respectively. There was no significant difference between cloxacillin and other DCT products in the cure of quarter IMI during the dry period up to 21 d postcalving. The pooled RR with the 95% CI was 1.00 (0.92 to 1.09). Similarly, there was no significant difference between cloxacillin and other DCT products in the cure of quarter Staphylococcus spp. IMI. The pooled RR with the 95% CI was 1.00 (0.96 to 1.06). The pooled RR with the 95% CI of quarter IMI cure using selective DCT, compared with no DCT, was 1.76 (1.23 to 2.54).

The objective of this study was to see if introduction of a 2-yr combined selective dry-cow therapy and teat-dipping trial would reduce clinical mastitis (CM) events in 164 Norwegian dairy herds. Three different penicillin or penicillin/dihydrostreptomycin-based dry-cow treatments, and 3 different teat-dipping regimens (negative control, iodine teat dip, or an external teat sealant) were independently and randomly allocated to each herd. Complete lactations both before and during the trial were investigated. Altogether, 1,005 CM cases were recorded in the lactations before the trial and 924 cases were recorded during the trial. Bacteriological milk samples were available from 784 of the 924 CM cases during the trial. Among these, Staphylococcus aureus were isolated from 47.4%, Streptococcus dysgalactiae from 22.5%, Escherichia coli from 10.7%, and coagulase-negative staphylococci from 6.3%. In addition, 12.5% cases were bacteriological negative, and the remainder of the CM cases were caused by other microbes. The different models were analyzed using Cox regression analysis with PROC PHREG and a positive stable frailty model in the SAS macro. Separate models were made for cows housed in tie-stalls and free-stalls. Parity had a significant impact on the CM risk in both type of stalls. Older cows (parity > 3) had the highest hazard ratio of contracting CM in tie-stalls (1.68) and free-stalls (2.18) compared with parity 1. The CM risk decreased significantly (13%) in tie-stalls and by 18% in free-stalls. In tie-stalls, iodine-dipped cows had a significantly lower chance (21%) of getting CM compared with the negative control and the use of external teat sealant. The same trend was seen in free-stalls; however, the differences were not significant. Compared with CM before the trial, the reduction of CM was 15% during the trial.

The objective was to promote a reduction in the prevalence of Staphylococcus aureus and Streptococcus dysgalactiae after 2 years of selective dry cow therapies and teat dipping/external teat sealant implementation. Three different dry cow treatments, one long-acting and two short-acting penicillin-based products were tested at herd level together with a negative control teat dipping group, an iodine teat dipping group and DryFlextrade mark, an external teat sealant. The regimes were independently randomly allocated to 178 dairy herds. Yearly bacteriological quarter milk samples were collected from all cows at the beginning of the trial, after 1 year and 2 years. At herd level, a total of 15% of the herds showed no Staphylococcus aureus isolates after 2 years, compared with 5% at the beginning. The distribution of Streptococcus dysgalactiae infected herds remained the same after 2 years. At cow level, there were no significant differences in the reduction of Staph. aureus between the different dry cow therapies and teat dipping regimes. But there was a significant reduction of Str. dysgalactiae in the iodine teat dipping group compared with Dryflextrade mark and the negative control group. The proportional rate of Staph. aureus positive quarters was reduced from 65.9% to 54.9% after 2 years. As for Str. dysgalactiae, an increase was observed from 14.2% to 15.2%.

Data from 350 herds enrolled in the Norwegian Dairy Herd Recording System (NDHRS) were used to investigate the associations between the first two cow-milk somatic cell counts (SCC) test-days' results after calving or the three last SCC test-days prior to drying off in the first lactation and the hazard ratio (HR) of clinical mastitis (CM) during the remaining first or the subsequent second lactation respectively. Altogether, 9519 first lactations and 6046 second lactations were included. Cox regression analyses adjusted for herd frailty effect were used. In the first lactation, SCC>40000 cells/ml on the first or second test-day was significantly associated with an increased risk of a CM event in the remaining first lactation. HR, compared with 10000 cells/ml, increased from 1.6 (1.4) for SCC of 40000-60000 cells/ml to 6.9 (4.2) for SCC >800000 cells/ml, when using the first (second) SCC test-day in the first lactation. Cows with a geometric mean of the three last SCC test-days between 50000 and 100000 cells/ml and between 401000 and 800000 cells/ml in the first lactation had HR of CM during the second lactation of 1.3 and 2.8 respectively compared with a reference group of 10000-20000 cells/ml. If a CM episode in the first lactation occurred, the HR for having a CM event during the second lactation was 1.5. There was a significant frailty effect which disappeared if the incidence rate of CM at herd level was included in the model.