Meta-analysis of dry cow management for dairy cattle. Part 1. Protection against new intramammary infections.

The objective of this study was to estimate the preventive effect of various dry cow management measures against quarter new intramammary infections (IMI) during the dry period up to 21 d postcalving. Moreover, the potential publication bias was assessed in the studies selected for this analysis. The intervention measures were blanket dry cow therapy (BDCT), selective dry cow therapy (SDCT), cloxacillin compared with other dry cow therapy products, and teat sealant. A meta-analysis relative risk (RR) was calculated per intervention and pathogen group when enough studies were available from the 33 selected studies. Results of the meta-analyses were examined using publication bias tests. Blanket dry cow therapy showed significant protection against new IMI caused by Streptococcus spp. [the pooled RR was 0.39 (0.30 to 0.51)] but no protection was observed against coliform new IMI [the pooled RR was 0.95 (0.81 to 1.10)]. After correction for publication bias, it became doubtful whether DCT is protective against new Staphylococcus spp. IMI. Cloxacillin showed similar protection against new quarter IMI compared with other DCT products [the pooled RR was 1.09 (0.94 to 1.25)]. Selective dry cow therapy showed higher protection against new IMI compared with no DCT [the pooled RR was 0.51 (0.30 to 0.86)]. However, BDCT showed more protection when compared with SDCT [the pooled RR was 0.55 (0.37 to 0.80)], but the inference about whether BDCT is superior to SDCT was dependent on whether the selection criteria for SDCT was at the cow or quarter level. Internal teat sealants showed significant protection against new IMI during the dry period [the pooled RR was 0.39 (0.18 to 0.82)]. Publication bias should be taken into account when attempts are made to review literature in a meta-analysis.