Cow-specific risk factors for clinical mastitis in Brazilian dairy cattle

Abstract

Information related to mastitis risk factors is useful for the design and implementation of clinical mastitis (CM) control programs. The first objective of our study was to model the risk of CM under Brazilian conditions, using cow-specific risk factors. Our second objective was to explore which risk factors were associated with the occurrence of the most common pathogens involved in Brazilian CM infections. The analyses were based on 65 months of data from 9,789 dairy cows and 12,464 CM cases. Cow-specific risk factors that could easily be measured in standard Brazilian dairy farms were used in the statistical analyses, which included logistic regression and multinomial logistic regression. The first month of lactation, high somatic cell count, rainy season and history of clinical mastitis cases were factors associated with CM for both primiparous and multiparous cows. In addition, parity and breed were also associated risk factors for multiparous cows. Of all CM cases, 54% showed positive bacteriological culturing results from which 57% were classified as environmental pathogens, with a large percentage of coliforms (35%). Coagulase-negative Staphylococcus (16%), Streptococcus uberis (9%), Streptococcus agalactiae (7%) and other Streptococci (9%) were also common pathogens. Among the pathogens analyzed, the association of cow-specific risk factors, such as Zebu breed (OR=5.84, 95%CI 3.77-10.77) and accumulated history of SCC (1.76, 95%CI 1.37-2.27), was different for CM caused by Coagulase-negative Staphylococcus and S. agalactiae in comparison to CM caused by coliforms. Our results suggest that CM control programs in Brazil should specially consider the recent history of clinical mastitis cases and the beginning of the lactations, mainly during the rainy season as important risk factor for mastitis.

<b>Etiological and molecular profile of pathogens causing clinical mastitis, and antimicrobial use in dairy herds</b>

“…Only one study was found in the recent indexed literature describing the CM profile in Brazilian dairy herds (OLIVEIRA et al, 2015). However, the estimation of CM was expressed as incidence risk (or cumulative incidence) as opposed to rate as we did, and the evaluation was performed at the cow-level, not at the quarter-level as in the current study.…”

“…Only one recent study characterizing CM in dairy herds in Brazil were found in the indexed literature, in which the mean annual incidence risk in primiparous cows was 27%, while for multiparous cows it was 31% (OLIVEIRA et al, 2015). Indices associated with the frequency of CM, such as prevalence, incidence rate, recurrence of cases, most prevalent etiological agents, and the association of such indices with herd-level descriptors were not found for dairy herds in Brazil.…”

“…Epidemiological studies have estimated the incidence rate of clinical mastitis (IRCM) in different regions of the world, including Europe (BRADLEY et al, 2007;VERBEKE et al, 2014;SANTMAN-BERENDS et al, 2015), North America (SARGEANT et al, 1998;OLDE RIEKERINK et al, 2008;, China (GAO et al, 2017), Australia (DANIEL et al, 1982), New Zealand (MCDOUGALL, 1999), andTanzania (KIVARIA;NOORDHUIZEN;MSAMI, 2007). However, studies describing indicators of CM, such as the most prevalent causing pathogens, distribution of severity score and the IRCM are few in Brazil (OLIVEIRA et al, 2015). Additionally, to our knowledge, no studies were conducted in Brazil associating the IRCM at the quarter-level and descriptors at the herd-level.…”

“…Factors such as season, herd size, housing system, average milk yield per cow, bulk milk somatic cell count (BMSCC), and bulk milk total bacterial count (BMTBC) may be associated with both the pathogens causing CM and the IRCM in dairy herds. Studies evaluating the association of herdlevel descriptors and the IRCM caused by specific groups of pathogens are few (VERBEKE et al, 2014), especially those evaluating Brazilian dairy herds where the etiology of CM may be different from that observed in countries with a more developed dairy industry (OLIVEIRA et al, 2015).…”

“…7 Group formed by cases with isolation of Gram-positive bacteria, with exception of contagious pathogens and Trueperella pyogenes. 8 Season categories were formed by the association of the two characteristic seasons in Southeast of Brazil [rainy (October-March); or dry (April-September); OLIVEIRA et al, 2015), and the years that each herd was evaluated in the study (2014 or 2015-2016). 9 Group formed by cases with isolation of Gram-negative bacteria.…”