Incidence Of Intramammary Infection Research Articles

Epidemiology of coagulase-negative staphylococci intramammary infection in dairy cattle and the effect of bacteriological culture misclassification

Objectives of this study were to identify the manageable risk factors associated with the lactational incidence, elimination, and prevalence of coagulase-negative staphylococci (CNS) intramammary infections (IMI) while taking into account the difficulties inherent to their diagnosis. A second objective was to evaluate the effect of CNS IMI misclassification in mastitis research. A cohort of 90 Canadian dairy herds was followed throughout 2007 to 2008. In each herd, series of quarter milk samples were collected from a subsample of cows and bacteriological culture was performed to identify prevalent, incident, and eliminated CNS IMI. Practices used on farms were captured using direct observations and a validated questionnaire. The relationships between herd CNS IMI prevalence and herd incidence and elimination rates were explored using linear regression. Manageable risk factors associated with the prevalence, incidence, or elimination of CNS IMI were identified via Bayesian analyses using a latent class model approach, allowing adjustment of the estimates for the imperfect sensitivity and specificity of bacteriological culture. After adjustment for the diagnostic test limitations, a mean CNS IMI quarter prevalence of 42.7% [95% confidence interval (CI): 34.7, 50.1] and incidence and elimination rates of 0.29 new IMI/quarter-month (95% CI: 0.21, 0.37) and 0.79 eliminated IMI/quarter-month (95% CI: 0.66, 0.91), respectively, were observed. Considerable biases of the estimates were observed when CNS IMI misclassification was ignored. These biases were important for measures of association with risk factors, were almost always toward the null value, and led to both type I and type II errors. Coagulase-negative staphylococci IMI incidence appeared to be a stronger determinant of herd IMI prevalence than IMI elimination rate. The majority of herds followed were already using blanket dry cow treatment and postmilking teat disinfection. A holistic approach considering associations with all 3 outcomes was used to interpret associations between manageable risk factors and CNS IMI. Sand and wood-based product bedding showed desirable associations with CNS IMI compared with straw bedding. Quarters of cows that had access to pasture during the sampling period had lower odds of acquiring a new CNS IMI and of having a prevalent CNS IMI. Many practices showed an association with only one of the CNS outcomes and should, therefore, be considered with caution.

Intramammary infections and teat canal colonization with coagulase-negative staphylococci after postmilking teat disinfection: Species-specific responses

Coagulase-negative staphylococci (CNS) are the most common pathogens associated with intramammary infections (IMI) in dairy cows. We hypothesized that postmilking teat disinfection would reduce microbial colonization of the teat canal and thus reduce the prevalence of IMI caused by certain CNS species. The efficacy of iodine postmilking teat dip was tested against CNS colonization of the teat canal, and incidence of IMI was measured. Using an udder-half model, 43 Holstein cows at the Washington State University Dairy were enrolled in the trial; postmilking teat dip was applied to one udder-half, treatment (TX), and the remaining half was an undipped control (CX). Teat canal swabbing and mammary quarter milk samples were taken in duplicate once a week for 16 wk for microbial culture. Isolates from agar cultures were presumptively identified as CNS and then speciated using PCR-RFLP and agarose gel electrophoresis. Colonization of the teat canal and IMI by CNS were assessed. Thirty CNS IMI were diagnosed and the number of new IMI in CX quarters (21) was significantly greater than that in TX mammary quarters (9). The majority of CNS IMI were caused by Staphylococcus chromogenes (30%) and Staphylococcus xylosus (40%), and the latter were appreciably reduced by teat dip. Except for S. xylosus, an association was observed between teat canal colonization and IMI by all CNS species in this study, in which the majority of IMI were preceded by teat canal colonization. The total number of CNS IMI was greater for CX group cows compared with TX group cows. However, the effect of disinfection on IMI did not appear to be the same for all CNS species.

Association of standing and lying behavior patterns and incidence of intramammary infection in dairy cows milked with an automatic milking system

The standing and lying behavior patterns of dairy cows, particularly the length of time cows spend standing after milking, have the potential to influence the incidence of intramammary infection (IMI). The objectives were to describe the standing and lying behavior patterns of cows milked with an automatic milking system (AMS) and to determine how these patterns relate to the incidence of IMI. One hundred and eleven lactating Holstein dairy cows were monitored over a 4-mo period. These cows were kept in a sand-bedded freestall barn with 2 pens, each with a free cow traffic AMS. Feed was delivered once daily, and pushed up 2 to 3 times daily. Quarter milk samples were collected for bacteriological culture from each cow once every 4 wk. A new IMI was defined as a positive culture sample following a negative culture. For 7 d before each of the last 3 milk samplings, standing and lying behavior, and times of milking and feed manipulation (feed delivery and push up) were recorded. Daily lying time and lying bout length were negatively related with milk yield (r=−0.23 and −0.20, respectively) and milking frequency (r=−0.32 and −0.20, respectively); milk yield was positively related to milking frequency (r=0.58). Feed manipulation near the time cows were milked (1h before 2h after) resulted in the longest post-milking standing times (mean=86min; 95% confidence interval=78, 94min), whereas feed manipulation occurring outside that time frame resulted in shorter post-milking standing times. Over the study period, 171 new IMI were detected. Of these new IMI detected, those caused by coagulase-negative staphylococci were the only ones associated with post-milking standing time; as post-milking standing time increased past 2.5h after milking, the odds of acquiring a new IMI tended to also increase. In summary, standing and lying behavior patterns of cows milked with an AMS were affected by both feed manipulation and their milking activity. Further, the post-milking standing time of cows milked with an AMS can be managed by providing fresh feed, as well as by pushing up feed, frequently throughout the day. Finally, cows that spend long periods of time (>2.5h) standing following milking may be at higher risk of acquiring a new CNS IMI.

The comparative efficacy of two long-acting dry-cow cephalonium products in curing and preventing intramammary infections

AIMS: To test equivalence between two different cephalonium dry-cow therapy (DCT) products with regard to the incidence of bacteriological cure of existing infections of quarters, the incidence of new intramammary infections (IMI) from 2–5 days postpartum and the incidence of clinical mastitis from drying-off to 21 days postpartum. METHODS: All cows (n=1,570) on four commercial dairy farms in Southland were eligible for inclusion. Power analysis using a variance inflation factor indicated a required minimum of 2,101 quarters per treatment group. Cows were blocked by herd, parity, previous history of mastitis and most recent somatic cell count (SCC), and then randomly allocated to either of two cephalonium treatments at the cow level, viz the treatment group (new formulation cephalonium) or the positive control group (existing reference formulation cephalonium). All quarters within a cow were assigned the same treatment. Samples collected from all quarters with a SCC ≥500,000 cells/mL at drying-off, and those with a positive culture postpartum were cultured, as well as samples from all quarters collected between 2–5 days postpartum. All cases of mastitis were recorded and sampled for culture. The risk of quarter-level incidence of bacteriological cure, IMI and clinical mastitis was modelled using a GLM and generalised estimating equation (GEE), including the effects of treatment group, age,farm, udder-health status at drying-off and length of dry period. RESULTS: For 829 infected quarters, the estimated incidence of bacteriological cure for all pathogens was 78.0 (95% CI=64.3–91.6)% for the treatment group and 75.7 (95% CI=61.6–89.8)% for the positive control group (p=0.71). Incidence of cure varied with the farm (p=0.001), type of pathogen pre-treatment (p=0.009) and log10SCC at drying-off (p<0.001). For 4,530 quarters, the estimated incidence of new IMI, with any pathogen, for treatment and positive control groups was 16.1 (95% CI=13.1–19.7)% and 16.0 (95% CI=13.0–19.5)% respectively (p=0.91). Incidence of IMI varied with farm (p<0.001), pathogen and SCC status before treatment (p<0.001), and length of the dry period (in days) (p<0.001). For 5,136 quarters, the estimated incidence of clinical mastitis was 1.0 (95% CI=0.5–1.7)% in the treatment group and 1.1 (95% CI=0.6–2.0)% in the positive control group (p=0.64). CONCLUSIONS: Use of the two different cephalonium products at drying-off in four dairy herds in Southland resulted in equivalence with respect to incidence of bacteriological cure of existing infections, incidence of new IMI postpartum, and incidence of clinical mastitis in early lactation.

The effect of selenium supplementation before calving on early-lactation udder health in pastured dairy heifers

Selenium (Se) deficiency has been associated with lowered resistance to mastitis in dairy cattle. However, little published data exists on the effect of Se supplementation before calving on udder health of pastured dairy heifers. Further, the relative efficacy of injectable barium selenate and oral organic Se for improving udder health in cows has not previously been tested. The objectives of this study were to determine the effects of precalving Se supplementation and type of supplementation on the blood activity of glutathione peroxidase and measures of udder health immediately after calving and during the first month of lactation in pastured dairy heifers. One hundred forty pregnant Chilean Holstein-Friesian heifers were fed a basal diet containing, on average, 0.15mg of Se/kg of dry matter. One month before predicted calving, heifers were allocated to 1 of 3 groups. Group 1 (n=49) received no supplementary Se, group 2 (n=46) received a single subcutaneous injection of Se (1mg/kg of live weight, as barium selenate), and group 3 (n=45) was fed Se yeast (3mg/heifer/d until calving). Heifers supplemented with barium selenate had a higher glutathione peroxidase activity from 14 d in milk onwards. Selenium supplementation, irrespective of source, tended to reduce the prevalence of intramammary infection (IMI) and decrease the prevalence of quarters with high somatic cell count (SCC) at calving. Overall, Se supplementation did not result in a reduction of the incidence of new IMI or clinical mastitis or in decreased SCC during the balance of the first month of lactation. However, in pasture-based heifers injected with barium selenate before calving, and fed diets with 1.3 and 2.5mg of Se/d precalving and during lactation, respectively, no cases of clinical mastitis were observed in the first month of lactation.

Stochastic bio-economic model of bovine intramammary infection

Although the dynamics of transmission play an important role in the occurrence of intramammary infection (IMI), they have not been considered in previous models used to estimate the cost of IMI. The bio-economic model described includes within-herd dynamics of pathogen-specific IMI. The model simulated Staphylococcus aureus, Streptococcus uberis, Streptococcus dysgalactiae, and Escherichia coli IMI stochastically and estimated the cost of these IMI in a herd of 100 dairy cows in a situation where a quota is applied to milk production. A Reed–Frost model was used for S. aureus, S. uberis, and S. dysgalactiae IMI and a Greenwood model for E. coli IMI. Economic analysis was conducted per pathogen for clinical and subclinical IMI. The parameters used in the model were based on the literature and were deemed credible and valid. Median annual incidence of clinical and subclinical IMI for all pathogens varied considerably. This variation was greatest for S. aureus IMI . The annual incidence of IMI in a herd of 100 dairy cows caused by S. aureus varied between 0 and 88 cases, with a median of 5 cases and the 5th and 95th percentiles of 0 to 36 for clinical IMI, and a median of 7 cases with the 5th and 95th percentiles of 0 to 52 for subclinical IMI. In consequence, the average total annual net costs also varied widely for S. aureus IMI. Clinical IMI costs were € 1375, with the 5th and 95th percentiles of 0 to 4716 and subclinical IMI costs were € 1219, with the 5th and 95th percentiles of 0 to 4030. The average annual net cost due to the 4 simulated pathogens combined was € 4896 and varied from € 915 to € 11,287 in a herd of 100 dairy cows. The bio-economic model developed for this study will be utilized as a tool to investigate the economic impact of management of pathogen-specific IMI.

Concentrations of Ganglioside Type M1 and Immunoglobulin G in Colostrum Are Inversely Related to Bacterial Infection at Early Lactation in Cows

The levels of IgG and ganglioside type M1 in the colostrum of cows and heifers were analyzed to examine their utility in predicting acquisition of intramammary infection (IMI) during the first weeks postpartum. In general, high levels of IgG and ganglioside type M1 in cows were associated with lower new incidence of IMI, and linear discriminate analysis based on these 2 variables yielded 69.4% successful classification into cows that did or did not acquire new IMI. This analysis was less successful in heifers because a high proportion of them joined the herd when already infected with bacteria in their udders. It is suggested that application of a wider range of measures that reflect the immune status would enable the identification of most cows prone to new IMI.

Effect of application of an external teat sealant and/or oral treatment with a monensin capsule pre-calving on the prevalence and incidence of subclinical and clinical mastitis in dairy heifers

AIM: To assess the effect of applying an external teat sealant or a slow-release intraruminal monensin capsule pre-calving on the prevalence and incidence of subclinical or clinical mastitis in dairy heifers post-calving. METHODS: The studies were undertaken in 13 herds. In two herds application of an external teat sealant was compared with a negative control; in nine herds treatment with monensin was compared with controls, and in two herds treatments were applied in a 2 × 2 factorial design. Heifers were randomly assigned within herd to be treated with a slow-release intraruminal device containing 32 g monensin (n=383), or left as untreated controls (n=389), approximately 30 days before the start of the spring calving period; or to be treated with a latex external teat sealant (n=206) when calving was impending, or be left as untreated controls (n=205). Milk samples were collected from each gland between 0 and 5 days after calving and from any gland diagnosed with clinical mastitis. The effect of the treatments on the prevalence of intramammary infection (IMI), i.e. subclinical mastitis, and clinical mastitis were initially analysed at the univariate level, with associated variables (p<0.2) being used in construction of multivariable models. RESULTS: The prevalence of IMI was 18.4% at the gland level, and coagulase-negative staphylococci followed by Streptococcus uberis were the most common isolates. Treatment with an external teat sealant reduced the prevalence, compared with controls, of any IMI (12.1 (SE 1.7)% vs 16.5 (SE 2.1)%, respectively; p=0.05) or IMI caused by a major pathogen (3.8 (SE 0.8)% vs 6.0 (SE 1.1)%, respectively; p=0.05). Monensin treatment did not affect the prevalence of any IMI (p=0.68) or IMI due to a major pathogen (p=0.11). The cumulative incidence of clinical mastitis was 14.2%. Neither monensin treatment (p=0.47) nor application of an external teat sealant (p=0.71) altered the risk of clinical mastitis. There was no interaction between the monensin and external teat sealant in the two herds where the treatments were applied in a 2 × 2 factorial design. CONCLUSIONS: Application of an external teat sealant resulted in a lower prevalence of any IMI and of an IMI caused by a major pathogen. Despite monensin reducing the mobilisation of body tissue and the risk of subclinical ketosis, it had no effect on the prevalence or incidence of IMI or clinical mastitis. CLINICAL RELEVANCE: Application of an external teat sealant is an option for reducing the prevalence of IMI in pasturefed dairy heifers.

Quarter-Level Analysis of Subclinical and Clinical Mastitis in Primiparous Heifers Following the Use of a Teat Sealant or an Injectable Antibiotic, or Both, Precalving

This study investigated the effect of infusion of a bismuth subnitrate teat canal sealant or an injectable antibiotic, or both, in heifers on the cure of existing intramammary infection (IMI), incidence of new IMI, prevalence of postcalving IMI, and incidence of clinical mastitis in the first 2 wk postcalving at the quarter level. Heifers (n = 1,067) in 30 seasonally calving, pasture-fed dairy herds were randomly assigned at the heifer level to 1 of 4 treatments (no treatment; 3 intramuscular injections of 5g of tylosin antibiotic at 24-h intervals; infusion of a teat sealant into all 4 quarters; 3 intramuscular injections of 5g of tylosin antibiotic and infusion of teat sealant into all 4 quarters). Mammary gland secretion samples were collected from each quarter of every heifer before treatment. Heifers within a herd were enrolled on one calendar day, 27 d (on average) before the planned start of the seasonal calving period. Duplicate milk samples were collected from each gland within 5 d after calving for bacterial culture and from glands the herdowners diagnosed as having clinical mastitis. The relative risk of effect of treatment on the incidence of cure, incidence of new IMI, prevalence of postcalving IMI, and incidence of clinical mastitis were calculated at the gland level using multivariate logistic regression analyses. Neither infusion of a teat sealant nor treatment with the injectable antibiotic increased the cure of precalving IMI. Infusion of the teat sealant reduced the risk of new IMI with any pathogen by 74%, reduced the prevalence of postcalving IMI by 65%, reduced the risk of new infection with Streptococcus uberis by 70% in quarters with an IMI precalving, and reduced the incidence of clinical mastitis from which a pathogen was isolated by 70% in quarters with an IMI precalving. Parenteral antibiotic treatment had no effect on any of these outcomes. In conclusion, use of an internal teat-canal sealant in heifers reduced the postcalving IMI prevalence and the incidence of pathogen-associated clinical mastitis postcalving by decreasing the incidence of new infections over this high-risk peripartum period, and may be a useful tool for reducing the risk of mastitis in heifers.

Interdependence of udder quarters for new intramammary infection during the dry period in cows submitted to selective antibiotic therapy

The aim was to investigate the interdependence of udder quarters within cow towards the incidence of intramammary infections during the dry period in herds under selective dry-cow antibiotic therapy. A total of 368 cows among 28 herds were included in a survey. Quarter milk samples collected at the last milking before drying-off and on day 3 after calving were submitted to microbiological procedures. An expected distribution of cows according to their number of newly infected quarters was calculated based on a binomial probability distribution from the overall quarter incidence (or from the quarter incidence in each herd) and compared with the observed distribution. Incidence of newly infected quarters ranged from 0.0 to 39.3%, depending on the herd (median: 17.7%). Interdependence of quarters towards new infection during the dry period was observed whatever the pathogen type, for both treated and untreated cows. Calculation of an expected distribution of cows according to their number of newly infected quarters using the quarter incidence in each herd (instead of the overall quarter incidence) reduced the distance to the observed distribution, but interdependence was still observed. Our results support the application of selective antibiotic therapy at the cow level rather than at the quarter level.

Incidence of intramammary infections during the dry period without or with antibiotic treatment in dairy cows – a quantitative analysis of published data

The study was aimed at summarising the literature that compares the incidence levels of spontaneously occurring intramammary infections (IMI) during the dry period, without versus with antibiotic dry cow treatment (DCT). A meta-analytic relative risk (RR) calculation was implemented when a priori relevant. Two main categories of comparison were used in the 36 selected papers. In the first category, the udder quarters were randomly allocated (at quarter or cow level) to an untreated or a treated group. Quarter incidence averaged 12.8% (weighted mean) in untreated quarters, and depending on the DCT used, from 6.6 to 8.0% in treated quarters. The meta-analytic RR of new IMI for untreated versus treated quarters varied from 1.54 to 1.94, depending on the DCT used. DCT was mainly found effective against IMI due to streptococci and coagulase-positive staphylococci. Based on only a few papers, the application of an internal teat sealer was associated to a quite similar (or possibly better) protection against IMI than DCT, but only in a subpopulation of particular (selected) cows. In the second category of studies, a selective dry cow or quarter antibiotic-treatment (selective DCT or DQT), according to cow or quarter selection criteria, was compared to blanket DCT. The meta-analytic RR of new IMI was 1.71 for selective DCT versus blanket DCT. Selective DQT seemed to be more at risk than selective DCT, but consisted of treating a much lower proportion of quarters. The summary-results provided by our meta-analysis should only be used with caution, due to possibly low external validity. More research seems to be relevant on the risk factors of new IMI during the dry period to make the outcomes of omission of DCT in selected cows more predictable under field conditions.

Removal of Hair Surrounding the Teat and Associated Bacterial Counts on Teat Skin Surface, in Milk, and Intramammary Infections

The effectiveness of monthly removal of hair surrounding teats on the reduction of teat skin surface bacteria, and the incidence of intramammary infection (IMI), was studied for 10 months in a dairy farm. A split udder design was used where hair was removed on one side, left or right, with the other side serving as a control. Controls and treatment sides were randomly applied in a systematic fashion to 218 cows. Standard milking time pre- and post-milking hygiene practices were applied to all udders during the trial. Collection of teat skin swab solutions preceded aseptic collection of milk samples, performed at monthly intervals, immediately prior to milking. Teat skin bacterial counts did not differ between control and treated teats. Incidences of IMI were similar for treatment when compared with control mammary quarters, as measured by total or by pathogen type. In a second study, the effect of hair removal on the bacterial content of milk was determined using 40 cows. Treatments and allocations were as described. Udder half milk, milk from both mammary quarters of each udder half, was combined and diverted into separate buckets. Buckets were thoroughly cleaned and sanitized between milkings. A portion of bucket milk was collected 24 h after removal of udder hair. The total milk bacterial counts, and counts of psychrotrophs and thermoduric organisms were not reduced by udder hair removal. Results do not suggest that removal of udder hair leads to an improvement in milk quality as determined by milk bacterial content in the herd studied.

Effects of automatic milking system on teat tissues, intramammary infections and somatic cell counts

To assess the impact of automatic milking systems (AMS) on the different aspects of milk production a research project involving both commercial and experimental dairy farms with different AMS and different management was started. This paper reports the results of a follow-up study on primiparous cows focused on assessing some markers to be used to monitor udder and teat health. Heifers were included after calving and sampled for at least 12 months. Quarter milk samples and teat measurements were taken to assess: intramammary infection (IMI) frequencies, somatic cell counts (SCC), teat thickness changes, teat skin and apex conditions. The study included 28 cows in herd A and 27 in herd B for a total number of 2344 samples. Overall, teat apex and skin conditions were maintained along the lactation. Teat skin conditions tended to decrease because of the accumulated number of milkings while lactation proceeded, but at a largely acceptable level in both herds. Teat apex conditions showed a decrease. Teat thickness changes displayed different patterns in the two herds, probably because of the different type of AMS, but in both cases a trend to decrease in thickness could be observed. The application of AMS in herd B, free from contagious pathogens, did not influence the frequency of IMI and the SCC. In herd A, characterized by the presence of Staphylococcus aureus IMI, the frequency of IMI showed a progressive increase, very likely as a consequence of the spread of infections during milking. Teat skin had no association with the frequency of IMI. Teat thickness changes outside values considered as physiological proved to be associated with decreased conditions in the teat apex score in herd A, but not in herd B. However, a decrease in teat apex score proved to be associated with an increase in IMI frequency in both herds. The results of this field trial confirm that AMS have no negative impact on IMI incidence, SCC and teat tissue conditions when the initial cow health status and overall herd management are good. In the presence of contagious pathogens, and when cows have more than 300 days in milk (DIM) the frequency of negative outcomes significantly increases and the proper control measures should be taken.

Management strategies to decrease the prevalence of mastitis caused by one strain of Staphylococcus aureus in a dairy herd.

The dairy herd at Washington State University had an outbreak of mastitis caused by a single strain of Staphylococcus aureus. The outbreak strain, termed novel, could not be controlled with routine contagious mastitis pathogen control procedures (incidence, 3.4 infections/100 cow months; peak prevalence > 22%). Our objective was to implement mastitis control measures that would decrease the incidence and prevalence of intramammary infection (IMI) caused by S aureus in the herd. The following intervention strategies were successfully implemented: strict segregation of cattle with IMI caused by S aureus, intensified culling of cattle with multiple-quarter IMI caused by S aureus, and inducing cessation of lactation of infected quarters in single-mammary-quarter infected cattle. One year after implementation of these control measures, incidence of IMI caused by S aureus was 0.35 infections/100 cow months, and prevalence had decreased from 20 to 8%.

Intramammary Infections in Primiparous Holsteins: Heritabilities and Comparisons of Bovine Leukocyte Adhesion Deficiency Carriers and Noncarriers

The objective of this study was to determine the impact of bovine leukocyte adhesion deficiency on intramammary infection (IMI) in Holstein cows at first calving. Quarter milk samples were collected between 3 d prepartum and 4 d postpartum from 756 Holstein cows in first lactation. These samples were frozen and subsequently cultured using National Mastitis Council recommendations. Sixty-eight carriers of bovine leukocyte adhesion deficiency were identified (9.0% of cows) from an additional milk sampling collected in early lactation. Binary variables (infected or uninfected) for each quarter were defined as dependent variables to evaluate IMI incidence from all bacterial species and major species groups: coliforms, coagulase-negative staphylococci, and streptococci other than Streptococcus agalactiae. The model included herd-season of calving, days in milk when samples were collected, age at calving, quarter, cow (random effect), and bovine leukocyte adhesion deficiency. Sire was included as a random effect (instead of cow), and bovine leukocyte adhesion deficiency was dropped from the model to estimate heritabilities. Heritabilities for IMI incidence from the various groups of organisms ranged from 0.02 to 0.66 (0.21 from all bacterial species).No differences were observed between carriers of bovine leukocyte adhesion deficiency and homozygous normal noncarriers for IMI from coliform, coagulase-negative staphylococci, streptococci other than Streptococcus agalactiae, or all bacterial species combined.

Efficacy of Postmilking Disinfection with Benzyl Alcohol Versus Iodophor in the Prevention of New Intramammary Infections in Lactating Cows

Five Michigan dairy herds participated in a split-herd study to compare the efficacy of two postmilking teat dips in the prevention of new intramammary infections (IMI) in lactating cows. Three hundred seventy cows were assigned to 4% benzyl alcohol, and 387 cows were assigned to 1% iodophor germicidal teat dip. The teat dips were applied by directly immersing the teats immediately after milking. Once a group was assigned to a teat dip, cows in that group maintained on that same teat dip throughout the trial. Total new IMI numbered 254 and 201 for cows treated with benzyl alcohol and iodophor germicidal teat dip, respectively. Staphylococcus spp. (52.0%), Staphylococcus aureus (20.1%), and Corynebacterium bovis (12.2%) were the predominant pathogens that caused new IMI in cows treated with benzyl alcohol. Staphylococcus spp., Staph. aureus, and C. bovis, respectively, were the pathogens responsible for 69.7, 12.4, and 4.5% of the new IMI in cows treated with iodophor. The incidences of new IMI caused by Staph. aureus (0.66 new IMI/100 milking quarters per mo), C. bovis (0.38 new IMI/100 milking quarters per mo), and all pathogens (3.15 new IMI/100 milking quarters per mo) were higher in cows treated with benzyl alcohol than in cows treated with iodophor (0.29, 0.11, and 2.35 new IMI/100 milking quarters per mo, respectively). Incidence of new IMI did not differ between groups for other pathogens. One percent iodophor prevented new IMI caused by contagious pathogens more effectively than did benzyl alcohol.

The effect of discontinuation of postmilking teat disinfection in low somatic cell count herds. II. Dynamics of intramammary infections

Summary Results of a 20 month split‐udder trial on the effect of discontinuation of postmilking teat disinfection on intramammary infections (IMI) with major and minor pathogens in seven dairy herds with a low somatic cell count are described. The incidence of Escherichia coli IMI was found to be significantly lower, whereas the incidence of IMI with Staphylococcus aureus and minor pathogens was significantly higher in quarters for which postmilking teat disinfection was discontinued than in disinfected quarters. It was concluded that discontinuation of postmilking teat disinfection decreased the incidence of E. coli IMI, accompanied by a, from a practical point of view, acceptable rise in somatic cell count. However, the possible increase in the incidence of S. aureus IMI calls for careful monitoring of the dynamics of IMI with contagious pathogens, when postmilking teat disinfection is discontinued in an attempt to reduce E. coli mastitis.

Effect of natural infection with minor pathogens on susceptibility to natural infection with major pathogens in the bovine mammary gland

Abstract Objective To evaluate the effect of natural udder infection with minor pathogens on subsequent natural infection with major pathogens. Sample population 7 dairy herds with low bulk milk somatic cell count. Procedure During a 20-month prospective study, milk samples were collected from dairy cows at regular intervals and from quarters with clinical signs of mastitis. Incidence of intramammary infection was calculated in uninfected quarters and in quarters infected with minor pathogens. A within-cow, matched case-control analysis was used to evaluate the effect of minor pathogens on subsequent infection with major pathogens. Results Quarters infected with minor pathogens had higher somatic cell count than did uninfected quarters. In quarters infected with Corynebacterium bovis, the rate of infection with major pathogens was lower, whereas in quarters infected with coagulase-negative Micrococcaceae, the rate of infection with major pathogens was higher than that in uninfected quarters. From the within-cow comparison, it appeared that, in quarters infected with minor pathogens, infection with major pathogens was significantly lower than that in comparable control quarters not infected with minor pathogens. Conclusions Minor pathogens have a protective effect against infection with major pathogens. The protective effect of C bovis against subsequent infection with major pathogens appears to be greater than the effect of coagulase-negative Micrococcaceae. (Am J Vet Res 1997;58:17–22)

Dietary vitamin E and selenium affect mastitis and milk quality.

Vitamin E and selenium (SE) are essential nutrients that are integral components of the antioxidant defense of tissues and cells. Soils in many of the important dairy regions of the world are Se-deficient, and feedstuffs grown on these soils will not provide adequate dietary Se. Cattle consuming stored forages are likely to be low in vitamin E unless supplemented, and vitamin E deficiencies are frequently observed in peripartum dairy cows. Many new intramammary infections (IMI) occur in the 2 wk before and after calving. Deficiencies of either vitamin E or Se have been associated with increased incidence and severity of IMI, increased clinical mastitis cases, and higher somatic cell counts (SCC) in individual cows and bulk tank milk. Somatic cell counts are a primary indicator of mastitis and milk quality in dairy herds. The polymorphonuclear neutrophil (PMN) is a major defensive mechanism against infection in the bovine mammary gland. A know consequence of vitamin E and Se deficiency is impaired PMN activity and postpartum vitamin E deficiencies are frequently observed in dairy cows. Dietary supplementation of cows with Se and vitamin E results in a more rapid PMN influx into milk following intramammary bacterial challenge and increased intracellular kill of ingested bacteria by PMN. Subcutaneous injections of vitamin E approximately 10 and 5 d before calving successfully elevated PMN alpha-tocopherol concentrations during the periparturient period and negated the suppressed intracellular kill of bacteria by PMN that commonly is observed around calving.

Epidemiology of Heifer Mastitis

Until recently, it had been assumed that primigravid heifers were seldom affected by intramammary infections (IMI) at or near parturition. Recent research results now suggest that this assumption is false. A number of studies report a high rate of IMI in heifers at or near parturition.(1-3) Interestingly, the pathogens associated with these IMI's appear to have a regional distribution. A study in the southern United States found a high prevalence of IMI associated with Staphylococcus aureus.(2) Studies in the New England and Southeastern United States detected a high prevalence of IMI associated with coagulase negative staphylococci.(1,3) IMI's associated with Staphylococcus aureus are related to histopathologic lesions in the mammary gland which suggest that these infections may hamper the normal development of the lactating gland.(4) These findings have prompted research to investigate the use of antibiotic therapy to decrease the risk of IMI. This research has found that antibiotics administered prior to calving will decrease the prevalence of peripaturient IMI.(5,6) A question that has not been answered is: Do these infections in heifers, particularly IMI by the minor pathogens, warrant treatment? The objectives of this paper are to report preliminary data describing the incidence of IMI in heifers, the pathogens involved in the infections and the subsequent rates of clinical mastitis in first lactation heifers conditional on the IMI status at freshening.