Randomized controlled non-inferiority trial investigating the effect of 2 selective dry-cow therapy protocols on antibiotic use at dry-off and dry period intramammary infection dynamics

Abstract

Selective dry-cow therapy (SDCT) could be used to reduce antibiotic use on commercial dairy farms in the United States but is not yet widely adopted, possibly due to concerns about the potential for negative effects on cow health. The objective of this study was to compare culture-and algorithm-guided SDCT programs with blanket dry-cow therapy (BDCT) in a multi-site, randomized, natural exposure, non-inferiority trial for the following quarter-level outcomes: antibiotic use at dry-off, dry period intramammary infection (IMI) cure risk, dry period new IMI risk, and IMI risk at 1 to 13 d in milk (DIM). Two days before planned dry-off, cows in each of 7 herds were randomly allocated to BDCT, culture-guided SDCT (cult-SDCT), or algorithm-guided SDCT (alg-SDCT). At dry-off, BDCT cows received an intramammary antibiotic (500 mg of ceftiofur hydrochloride) in all 4 quarters. Antibiotic treatments were selectively allocated to quarters of cult-SDCT cows by treating only quarters from which aseptically collected milk samples tested positive on the Minnesota Easy 4Cast plate (University of Minnesota, St. Paul, MN) after 30 to 40 h of incubation. For alg-SDCT cows, antibiotic treatments were selectively allocated at the cow level, with all quarters receiving antibiotic treatment if the cow had either a Dairy Herd Improvement Association test somatic cell count >200,000 cells/ mL during the current lactation or 2 or more clinical mastitis cases during the current lactation. All quarters of all cows were treated with an internal teat sealant. Intramammary infection status at enrollment and at 1 to 13 DIM was determined using standard bacteriological methods. The effect of treatment group on dry period IMI cure, dry period new IMI, and IMI risk at 1 to 13 DIM was determined using generalized linear mixed models (logistic), with marginal standardization to derive risk difference (RD) estimates. Quarter-level antibiotic use at dry-off for each group was BDCT (100%), cult-SDCT (45%), and alg-SDCT (45%). The crude dry period IMI cure risk for all quarters was 87.5% (818/935), the crude dry period new IMI risk was 20.1% (764/3,794), and the prevalence of IMI at 1 to 13 DIM was 23% (961/4,173). Non-inferiority analysis indicated that culture-and algorithm-guided SDCT approaches performed at least as well as BDCT for dry period IMI cure risk. In addition, the final models indicated that the risks for each of the 3 IMI measures were similar between all 3 treatment groups (i.e., RD estimates and 95% confidence intervals all close to 0). These findings indicate that under the conditions of this trial, culture-and algorithm-guided SDCT can substantially reduce antibiotic use at dry-off without negatively affecting IMI dynamics.

Randomized equivalence study comparing the efficacy of 2 commercial internal teat sealants in dairy cows

“…In addition, the prevalence of IMI caused by Staphylococcus aureus (0.4% of quarters at risk) and gram-negative pathogens (0.5%) was low. The quarterlevel prevalence of IMI at 1 to 13 DIM was 12.8%, which is slightly less than other multi-herd studies of DCT protocols using ITS in the United States, which found risks of 23.0% (Rowe et al, 2020a), 23.0% (Johnson et al, 2016), and 14.7% (Arruda et al, 2013). The profile of pathogens causing IMI at 1 to 13 DIM in the current study was similar to the aforementioned studies, with gram-positive (324 of 358 infected quarters, 90.1%) and NAS being the predominant causes (225 of 358, 62.8%) and gram-negative pathogens being uncommon (32 of 358, 1.1%).…”

Randomized controlled field trial comparing quarter and cow level selective dry cow treatment using the California Mastitis Test

“…If barriers for DO at quarter level are overcome, our study shows AB use at DO can be substantially reduced by a range of 11 to 57% in study herds. This reduction would be on top of antibiotic reductions of 21% (Cameron et al, 2014) and 55% (Rowe et al, 2020a) as shown by others to already be achieved by switching from blanket to selective dry cow treatment at the cow level. Such approaches are in line with recommendations of prudent AB use coming from a growing concern regarding the potential for AB use in food animals to promote the future emergence of antimicrobial resistance in bacteria (O'Neill, 2014).…”

“…Antibiotic dry cow treatment is widely used for the cure and prevention of IMI (Halasa et al, 2009a,b). Three strategies have been recommended (Kabera et al, 2020;Rowe et al, 2020a): treatment of all cows to be dried off with antibiotics (AB) regardless of infection status (blanket cow level treatment, BCLT), treatment of all 4 quarters of infected cows (selective cow level treatment, SCLT), and treatment of infected quarters (selective quarter level treatment, SQLT).…”

Taurine reprograms mammary-gland metabolism and alleviates inflammation induced by Streptococcus uberis

“…Mastitis remains an ongoing health problem, especially when caused by persistent intracellular bacterial infection, such as S. uberis (1,7). Recent ndings in our lab have shown that in ammation is tightly controlled, which protects the host from excessive or chronic damage induced by this process (13).…”

“…More than 150 different pathogens can cause mammary gland infection and no speci c vaccines are available. Antibiotics combined with anti-in ammatory drug therapy is the usual method to control mastitis (1). These therapies are often ineffective for the diversity of pathogens and the complexity of breast tissue (2,3).…”