Comparing Blanket vs. Selective Dry Cow Treatment Approaches for Elimination and Prevention of Intramammary Infections During the Dry Period: A Systematic Review and Meta-Analysis

Abstract

A systematic review and a series of meta-analyses were conducted to investigate the efficacy of selective dry cow antimicrobial treatment (SDCT) (in which only infected quarters/cows were treated with an antimicrobial) compared with blanket dry cow treatment (BDCT) (all quarters/all cows received an antimicrobial, regardless of their infection status). A full detailed protocol was published before initiating this review. Studies reporting on the (1) proportion of untreated quarters or cows when using SDCT, (2) intramammary infection (IMI) incidence risk over the dry period, (3) IMI elimination risk, (4) post-calving IMI prevalence, (5) early lactation clinical mastitis incidence, or (6) subsequent lactation milk yield and somatic cell counts were considered eligible. Thirteen articles representing 12 controlled trials, whether randomized or not, were available for analyses. SDCT reduced the use of antimicrobials at dry off by 66% (95% CI: 49-80). There was no difference in the elimination of existing IMI at dry off, between SDCT and BDCT. Meta-regression showed that the risk of IMI incidence during the dry period, IMI risk at calving, early lactation clinical mastitis risk, and early lactation milk yield and somatic cell counts did not differ between SDCT and BDCT as long as an internal teat sealant (65% bismuth subnitrate) was administered to untreated healthy quarters/cows at dry off. For trials not using internal teat sealants, SDCT resulted in higher risk than BDCT of acquiring a new IMI during the dry period and of harboring an IMI at calving. Lines of evidence strongly support that SDCT would reduce the use of antimicrobials at dry off, without any detrimental effect on udder health or milk production during the 1st months of the subsequent lactation, if, and only if, internal teat sealants are used for healthy, untreated quarters/cows.

Keywords: antimicrobial use; dairy cows; dry period; intramammary infection; selective antimicrobial treatment.

Figure 1

Result of the different steps for searching and identifying relevant records for the systematic review and meta-analysis on antimicrobial-based dry cow therapy approaches. The search was conducted to answer three research objectives: (1) choice of antimicrobial at drying off; (2) comparison of blanket vs. selective dry cow treatment; and (3) complementing an antimicrobial treatment with a teat sealant. The gray box indicates results specific for objective (2), comparison of blanket vs. selective dry cow treatment, and the other two objectives will be presented in subsequent independent articles. Screening of references cited by the included articles was also conducted but did not lead to the addition of eligible articles specific to the comparison of selective and blanket dry cow therapies. This latter part of the search strategy will be presented for the other two objectives in the subsequent associated articles. NMC, National Mastitis Council; AABP, American Association of Bovine Practitioners.

Figure 2

Proportion of studies with a given risk of bias among 12 trials included in a systematic review comparing selective dry cow therapy and blanket dry cow therapy.

Figure 3

Forest plots showing the proportion of antimicrobial use reduction.

Figure 4

Forest plots showing the effect of selective dry cow treatment compared with blanket dry cow therapy on risk of acquiring new IMI during the dry period, grouped by studies where untreated cows/quarters with antimicrobial received an internal teat sealant (ITS = Yes) and those where they did not receive an internal teat sealant (ITS = No).

Figure 5

Forest plots showing the effect of selective dry cow treatment compared with blanket dry cow therapy on risk of IMI elimination during the dry period.

Figure 6

Forest plots showing the effect of selective dry cow treatment compared with blanket dry cow therapy on risk of IMI prevalence at calving.

Figure 7

Forest plots showing the effect of selective dry cow treatment compared with blanket dry cow therapy on risk of acquiring CM during the first 4 months of lactation.

Figure 8

Forest plot illustrating the mean difference in milk production (kg/day) during the first 4 months of lactation after a selective dry cow treatment approach, in comparison with a blanket dry cow therapy.

Figure 9

Forest plot illustrating the mean difference in somatic cell counts (on a natural logarithm scale) during the first 4 months of lactation after a selective dry cow treatment approach, in comparison with a blanket dry cow therapy.