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The development of reliable models for transmission of intramammary infections (IMI) is the subject of extensive research. Such models are useful to enhance the identification and understanding of factors that affect pathogen-specific IMI dynamics. Longitudinal transmission models are valuable for predicting infection outbreak risks, quantifying the effectiveness of response tactics, and performing response planning. In this work, we focused on modeling Corynebacterium spp. by using a compartmental model. Previous investigations have considered modeling the transmission dynamics of several bacterial pathogens, but not Corynebacterium spp. We established a Corynebacterium spp. Susceptible-Infectious-Susceptible (SIS) model. We simulated the model numerically by using parameters that we estimated by a generalized linear model approach, using month of study as the time variable. The data, from which the parameters of the model were estimated, were obtained in a field trial conducted in 2 US dairy herds. Altogether, 786 cows were sampled at least once during the 13-mo study period. The total number of quarter milk cultures and cases of IMI caused by Corynebacterium spp. were 11,744 and 556, respectively, in farm A; the corresponding figures for farm B were 11,804 and 179. Our modeling study included only transmission from persistent IMI caused by Corynebacterium spp. within the lactation pens. The rate of new infections was significantly related to preexisting IMI in both farms, underscoring the importance of preexisting Corynebacterium spp. IMI for the transmission of Corynebacterium spp. within lactation pens. The estimated basic reproduction numbers (R 0 ) in the 2 farms were 1.18 and 0.98, respectively. The nonsignificant disparity in R 0 was associated with significant differences in cure rates between farms., (Copyright © 2018 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

The objective of the study was to explore the relationship between herd dry period (DP) intramammary infection (IMI) incidence and elimination rates. A cohort of 91 Canadian dairy herds was recruited and followed in 2007 and 2008. Universal dry cow therapy was widely adopted among the participating herds. At the beginning of years 2007 and 2008, a sample of 15 cows was selected in each herd. A series of quarter-milk samples consisting of 2 predry and 2 postcalving samples were collected on each quarter of these 30 cows. Milk samples were analyzed using routine bacteriological milk culture, and predry and postcalving IMI statuses of these quarters were established using parallel interpretation of the 2 predry and 2 postcalving tests, respectively. Intramammary infection status was defined as IMI by Staphylococcus aureus, streptococci other than Streptococcus agalactiae, coagulase-negative staphylococci (CNS), or Corynebacterium spp. Incidence and elimination rates of DP IMI were computed for each herd. Lowess curves and linear regression were used to investigate the association between DP IMI incidence and elimination rates. Significant negative associations were found between incidence and elimination rates of Staph. aureus and CNS. The relationship between incidence and elimination rates was nonlinear for CNS, with a relatively strong negative relationship between DP IMI incidence and elimination rates for herds with relatively low DP IMI incidence (<0.10 new IMI/quarter-month). For herds with higher DP IMI incidence (≥ 0.10 new IMI/quarter-month), a weaker negative relationship was observed between rates. No significant associations could be seen between DP incidence and elimination rates of streptococci other than Strep. agalactiae and of Corynebacterium spp. These results suggest that, conversely to the general belief, acquisition of new IMI and elimination of existing IMI during the DP may be driven, at least for staphylococci, by common mechanisms. The use of management strategies that would lead to the selection of pathogens less well adapted to the host could explain the associations observed between acquisition and elimination of IMI over the DP., (Copyright © 2013 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

The efficacy of 2 iodine barrier teat dips was compared with a conventional iodine postmilking teat dip. The products were evaluated using a natural exposure trial on a 250-cow dairy based on the National Mastitis Council guidelines. Bacteriological samples were taken every 2 wk over 6 mo. All dips contained 1.0% available iodine and high levels of free iodine for germicidal efficacy. Barrier 1 was an experimental dip containing 14 to 20 ppm of free iodine, barrier 2 contained 8 to 14 ppm of free iodine, and the nonbarrier control contained 12 to 16 ppm of free iodine. The average free iodine for barrier 1 and barrier 2 combined was 14 ppm, which was equal to the average free iodine for the positive control. A 21% reduction of new intramammary infections (IMI) was observed for the 2 barrier dips combined when compared with the nonbarrier control. A significant reduction of 38% was observed for the clinical infection rate for barrier 1 when compared with barrier 2; however, barrier 1 did not significantly reduce the subclinical IMI when compared with barrier 2. Barrier 1 significantly reduced the combined clinical and subclinical IMI by 24% when compared with the positive control. The skin condition showed slight variation among the dips over the course of the trial, but no difference was observed at the end of the trial. Barrier 1, with the highest concentration of free iodine, gave the best efficacy results of all 3 dips.

Effectiveness of a polyethylene intramammary device against naturally occurring infections was evaluated in three Maryland herds over 2 yr. Treated cows [62] were fitted with intramammary devices in all quarters of udders. Control cows [62] were sham treated. Rates of new intramammary infection over single lactation in treated and control quarters of primiparous cows averaged 18 and 27%. Reduction of infection rate was due primarily to fewer Corynebacterium bovis infections. Infection rate between multiparous cow treatments were similar. In uninfected quarters cell counts in strippings averaged .11 to .13 X 10(6)/ml and in quarters fitted with intramammary devices concentrations were only .22 to .31 X 10(6) cells/ml. But in infected quarters with intramammary devices, cell counts of strippings were 1.38 to 1.48 X 10(6)/ml. Concentrations of somatic cells of strippings in infected quarters without devices averaged .48 to .63 X 10(6)/ml. Dairy herd improvement cell counts for primiparous and multiparous cows with and without intramammary devices were similar and averaged .2 X 10(6)/ml. Neither milk nor fat production differed. The intramammary device as currently designed is incapable of stimulating a leukocytosis sufficient in stripping milk to prevent intramammary infection.

Rates of environmental streptococcal and coliform intramammary infections were compared among quarters uninfected and infected with either Corynebacterium bovis or Staphylococcus species. Rate of environmental streptococcal intramammary infections was 3.9 times greater in C. bovis-infected quarters than in uninfected quarters. Rate of environmental streptococcal infections was 2.6 times greater in quarters infected with Staphylococcus species than in uninfected quarters. Rate of coliform intramammary infections did not differ among quarters with differing bacteriological infection statuses. Quarters infected with either C. bovis or Staphylococcus species had higher milk SCC than did uninfected quarters. Intramammary infection with either Corynebacterium bovis or Staphylococcus species did not protect quarters against coliform infection. Rate of environmental streptococcal infections was enhanced in quarters infected with either C. bovis or Staphylococcus species.