Meta-analysis of dry cow management for dairy cattle. Part 1: Protection against new intramammary infections, and Part 2: Cure of existing intramammary infections.

 In a large study this question was addressed in two papers: in the first paper the preventive effect of various dry cow measures on new infections were investigated and in the second paper the cure of existing infections. These studies are unique in the sense that a highly powerful statistical method, called meta-analysis, was used which enable scientists to pool research data from various studies conducted in different circumstances and synthesize a highly reliable result which for all practical purposes can be considered correct to implement. The titles of the respective papers published by T. Halasa and co-workers in the Journal of Dairy Science, Volume 92 of 2009, page 3134 to 3149 and page 3150 to 3157 are: Meta-analysis of dry cow management for dairy cattle. Part 1. Protection against new intramammary infections and Part 2. Cure of existing intramammary infections.

The main goal of dry cow therapy is to cure existing intramammary (in the udder) infections and to prevent new infections. Previous studies indicated that Staphylococcus aureus (the most prominent organism responsible for mastitis) infection during the dry period is mainly due to contamination of the teats after the last milking of the lactation period. What also became clear was that treatment with antibiotics at the beginning of the dry period could provide nearly full protection against infection by species of both Staphylococcus and Streptococcus (another important organism of mastitis). The latter result also has implications for re-infection, since although the risk of new infection by various environmental organisms is high in the early and late dry period, the risk for the above mentioned contagious organisms is much lower during the dry period than during other times. This means that treatment against these organisms during the beginning of the dry period should to a large extent protect the cow during the rest of the dry period. The antibiotic treatment practices followed were primarily all-inclusive, known as "blanket treatment", which in recent times became questionable because of emerging antibiotic bacterial resistance and economic reasons. The blanket practice has therefore largely been replaced by selective dry cow treatment based on cow characteristics such as somatic cell counts near dry off or the intramammary infection history of the cow. An alternative to blanket and selective dry cow treatment with appropriate antibiotics is the use of an internal or external teat sealant, which is meant to prevent access of the organism to the interior of the udder. Research results where these different methods were used and which were documented in some 20 to 30 papers depending on the questions addressed, were re-analysed by the present authors with the meta-analysis technique. The main results are summarized in the next paragraph.

As far as protection against re-infection is concerned: 1) Dry cow therapy provided effective protection for new udder quarter infection caused by Streptococcus species during the dry period and up to 21 days after calving. 2) No protection was indicated against new coliform (environmental) species and the combined results casted doubt whether the protection against new Staphylococcus invasion was effective. 3) The therapeutic agent cloxacillin provided similar protection against all new quarter infections and was similarly effective against newly infecting Staphylococcus species compared with other dry cow treatments. 4) Selective dry cow treatment provided substantial protection against new quarter infection when compared with no treatment, but was less effective compared with blanket dry cow treatment. 5) Teat sealants mostly were effective against re-infection. As far as curing is concerned: a) Blanket and selective dry cow treatment cured 80% more effectively than no dry cow treatment. b) The cure efficacy of blanket treatment for Streptococcus species was similar to that for Staphylococcus species. c) The cure efficacy with cloxacillin in curing quarter intramammary infection from all organisms, and specifically from Staphylococcus species up to 21 days after calving, was similar to that of the standard dry cow treatment products used.

Bottom line: The various dry cow treatments discussed should be effective under most circumstances; the actual ones implemented will depend on economics and the incidence and severity of mastitis on the specific dairy farm.