Survey of intramammary infections in ewes on the New England Tableland of New South Wales

Samples of mammary secretion were collected aseptically from 1093 ewes in 8 separate flocks. Most of the ewes were suckling lambs 4 to 6 weeks old. Standard bacteriological tests were carried out on the samples to identify the organisms involved in intramammary infections. Data on age, breed, lactational status and clinical status of the gland and its secretion were recorded at the time of sampling. The prevalence of intramammary infection was 14% of ewes (8% of glands). There was a tendency for prevalence of intramammary infection to be positively correlated with age of the ewe (two-year-old and six-year-old ewes had, respectively, 4.4% and 14.0% of glands infected). This relationship was highly significant for Border Leicester x Merino ewes. There were also significant differences in infection prevalence between breeds. infected glands had a higher prevalence of clinical abnormalities of udder, teat and secretion than did non-infected glands. Staphylococcus aureus was overwhelmingly the most frequently isolated bacterium being responsible for 40% of all intramammary infections.     

Approaches to modeling intramammary infections in dairy cattle

In this paper, three approaches (Markov processes, discrete-event simulation, and differential equations) to modeling intramammary infections (IMI; focusing on the dynamic changes between uninfected, subclinical, and clinical udder-health states) are described. The objectives were to describe the various approaches to modeling intramammary infections, determine if simulations of the examples of the three approaches yield stable prevalences, and discuss the approaches' limitations. The literature review showed that there is no agreement on the proportion of animals that change health states. The approach of discrete-event simulation modeling included the most cow-level risk factors and udder-health states (hence, was judged to replicated best the dynamics of the infection process) and yielded stable prevalences for all udder-health states. However, there remain parts of the dynamics that need further research. These include the pathogen-specific probabilities and times of occurrence for: regression of clinical IMI to subclinical IMI, flare-up of subclinical IMI to clinical IMI, and incidence of subclinical IMI. Also, the assumption in all current approaches of homogenous mixing is violated because the primary contact structure for contagious pathogens during milking is either between cows through residual infectious milk in the milking machine or within a cow by vacuum fluctuations or teat-cup liner slips. Better contact structures should be incorporated so that the effects of control strategies can be better-estimated. Moreover, the three modeling approaches discussed assumed that all non-infected quarters are susceptible to infection—which might be denied by work in genetic resistance.     

Intramammary antibiotic treatment at the end of lactation for prophylaxis and treatment of intramammary infections in ewes

Ewes treated by intramammary infusion of cephapirin benzathine at the end of lactation were less likely to develop new intramammary infections by early in the next lactation. A controlled clinical trial involving 135 treated ewes and 145 untreated control ewes evaluated the prophylactic and treatment efficacy of intramammary antibiotic treatment of ewes at the time of weaning lambs. Milk samples for bacteriologic examination and identification of intramammary infections were collected at weaning of lambs and 1 to 3 weeks into the subsequent lactation. Untreated ewes were 2.6 times more likely than treated ewes to develop new intramammary infections between sampling times. Existence of an intramammary infection in one mammary gland significantly increased the risk of the other mammary gland becoming infected. Treatment also appeared to be associated with a higher cure rate of existing infections.     

Phenotypic and genotypic identification of streptococci and related bacteria isolated from bovine intramammary infections

Background

Streptococcus spp. and other Gram-positive, catalase-negative cocci (PNC) form a large group of microorganisms which can be found in the milk of cows with intramammary infection. The most frequently observed PNC mastitis pathogens (major pathogens) are Streptococcus uberis, Strep. dysgalactiae, and Strep. agalactiae. The remaining PNC include a few minor pathogens and a large nonpathogenic group. Improved methods are needed for the accurate identification and differentiation of PNC.A total of 151 PNC were collected from cows with intramammary infection and conclusively identified by 16S rRNA sequencing as reference method. Nine phenotypic microbiological tests (alpha-hemolysis, CAMP reaction, esculin hydrolysis, growth on kanamycin esculin azide agar and on sodium chloride agar, inulin fermentation, hippurate hydrolysis, leucine aminopeptidase and pyrrolidonyl peptidase activity), multiplex PCR for the three major pathogens (target genes for Strep. uberis, Strep. dysgalactiae and Strep. agalactiae: pauA, 16S rRNA, and sklA3, respectively), and mass spectroscopy using the matrix-assisted laser desorption ionization-time of flight (MALDI-TOF MS) were evaluated for the diagnosis and discrimination of the three clinically most relevant PNC.

Results

The probability that a strain of Strep. uberis, Strep. dysgalactiae and Strep. agalactiae was correctly identified by combining the results of the 9 phenotypic tests was 92%, 90%, and 100%, respectively. Applying the multiplex PCR, all strains of the three major pathogens were correctly identified and no false positive results occurred. Correct identification was observed for all strains of Strep. uberis and Strep. agalactiae using MALDI-TOF MS. In the case of Strep. dysgalactiae, some variability was observed at the subspecies level, but all strains were allocated to one single cluster.

Conclusions

The results of the present study show that reliable identification of the clinically most relevant PNC (Strep. uberis, Strep. agalactiae and Strep. dysgalactiae) can be obtained by use of a combination of colony morphology, hemolysis type and catalase reaction, and a multiplex PCR with specific primers restricted to these 3 pathogens. The MALDI-TOF MS is a fast method that shows promising results, although identification of Strep. dysgalactiae at the subspecies level is not yet satisfactory.     

Clinical features of consecutive intramammary infections with Streptococcus agalactiae in vaccinated and non-vaccinated heifers

The clinical, haematological and functional changes which followed three consecutive intramammary infections of Streptococcus agalactiae in the first lactation of eight heifers, four of which were systemically hyperimmune to the organism, are described. Irrespective of whether it was a vaccinated or non-vaccinated heifer or first, second or third infection the clinical features during the first 24 hours were characterised by elevated temperatures with hard, swollen and painful infected quarters. First infections were almost all of short duration because of self cure, while second or third infections were prolonged, with intermittent excretion of bacteria and low cell counts. Milk yields of infected quarters were depressed, ranging from 8 per cent in short infections to 31 per cent in chronic infections. All blood parameters remained within normal limits with the exception of total and differential white cell counts, which showed a change from a quantitative to a qualitative response by the third infection. The most significant finding was the absence of any real difference between the systemically hyperimmune and the non-vaccinated heifers, suggesting that circulating antibody has little effect against intramammary infection.     

Non-clinical intramammary infection in lactating ewes and its association with clinical mastitis

A bacteriological survey for the study of non-clinical intramammary infection in the sheep udder was carried out in 88 Assaf ewes. A mean infection prevalence in the first few weeks of lactation was 55%. The most common bacterial isolates were Micrococcus spp. followed by coagulase negative staphylococcus, together accounting for 93% of the total number of isolates. An infection prevalence of 54% was found in ewelambs 2 days after their first lambing, indicating a marked new infection rate around lambing. Generally, the course of lactation was characterized by dynamic changes of new infection and spontaneous resolution. About 5% of half udders examined developed clinical mastitis. The comparison of bacteriological data from mastitic milk samples and from samples taken from the same half udders before the appearance of the clinical disease could not support the theory that in sheep, mastitis is a clinical exacerbation of a non-clinical intramammary infection.     

Host-response patterns of intramammary infections in dairy cows

Many different bacterial species have the ability to cause an infection of the bovine mammary gland and the host response to these infections is what we recognize as mastitis. In this review we evaluate the pathogen specific response to the three main bacterial species causing bovine mastitis: Escherichia coli, Streptococcus uberis and Staphylococcus aureus. In this paper we will review the bacterial growth patterns, host immune response and clinical response that results from the intramammary infections. Clear differences in bacterial growth pattern are shown between bacterial species. The dominant pattern in E. coli infections is a short duration high bacteria count infection, in S. aureus this is more commonly a persistent infection with relative low bacteria counts and in S. uberis a long duration high bacteria count infection is often observed. The host immune response differs significantly depending on the invading bacterial species. The underlying reasons for the differences and the resulting host response are described. Finally we discuss the clinical response pattern for each of the three bacterial species. The largest contrast is between E. coli and S. aureus where a larger proportion of E. coli infections cause potentially severe clinical symptoms, whereas the majority of S. aureus infections go clinically unnoticed. The relevance of fully understanding the bovine host response to intramammary infection is discussed, some major gaps in our knowledge are highlighted and directions for future research are indicated.     

Relationships between teat-end bacteria and intramammary infections

Teat-end populations of staphylococci and streptococci were studied on teat apices of an experimental herd. Individual cows were found to have higher numbers of some of these microorganisms than other cows and certain teats had consistently higher populations than other teats in the same individual. A positive relationship was found between the numbers of staphylococci on teat-ends and presence of intramammary infections of the quarters. High teat-end bacterial numbers were present prior to the laboratory recognition of intramammary infections.     

Duration of bovine intramammary infections in commercial dairy herds

Data on the infection status of cows on seven commercial dairy farms were collected over 492 full lactations. Foremilk samples were taken at an average interval of five weeks. A total of 249 streptococcal and 433 staphylococcal infections were diagnosed. Spontaneous elimination occurred in 49 per cent of all streptococcal infections and in 54 per cent of Staphylococcus aureus infections. The average duration of spontaneously eliminated infections was 10.8 weeks for Streptococcus agalactiae, 9.9 weeks for Strep dysgalactiae, 10.4 weeks for Strep uberis and 12.8 weeks for Staph aureus. The average duration of infections persisting until drying off was 19.3 weeks for Strep agalactiae, 18.7 weeks for Strep dysgalactiae, 18.5 weeks for Strep uberis and 25.2 weeks for Staph aureus. The method and rate of elimination of infection as found in this analysis are of value for estimating new infection rates and selecting quarters for dry cow therapy.     

Prevalence and incidence of intramammary infections in lactating dairy goats

AIM: To determine the prevalence of intramammary infection (IMI) of lactating dairy goats between 0 and 4 days postpartum, the prevalence and incidence rate of new IMI at Weeks 2, 14 and 27 of lactation, and the relationship between herd-level prevalence of IMI and bulk tank somatic cell count (BTSCC).

METHODS: Milk samples were collected from 8% of a herd (total 624 does) from 18 dairy goat herds in the Waikato region of New Zealand, for bacteriology and somatic cell count (SCC) determination, from both glands within 4 days of kidding (Week 0) and again at Weeks 2, 14 and 27. Prevalence of IMI was determined at each time point and incidence rate calculated for Weeks 0–2, 2–14, and 14–27. Greenwood and Reed-Frost models were compared for estimation of the transmission parameter for all pathogens, and for Staphylococcus aureus, coagulase negative staphylococci (CNS) and Corynebacterium spp. separately.

RESULTS: Bacteria were isolated from 1,122/4,814 (23.3%) glands, with CNS (13.4%) and Corynebacterium spp. (7.3%) being the most common isolates. Prevalence of any IMI increased with stage of lactation, varied among herds, and increased with age (all p<0.05). Incidence rate was 80, 24 and 7 new IMI/10,000 gland days for Weeks 0–2, 2–14 and 14–27, respectively. Incidence rate for any IMI increased with age and with the presence of an IMI in the contralateral gland, and varied among herds (p<0.001). The transmission of each pathogen was better modelled assuming contagiousness (Reed-Frost models), than not (Greenwood models).

At gland level, IMI increased SCC at all stages of lactation (p<0.001). The gland prevalence of IMI within herds was positively associated with ln BTSCC at Week 2 (p=0.02), but not Weeks 14 or 27 (p>0.05).

CONCLUSIONS: Prevalence of IMI increased with stage of lactation, but the highest incidence rate of new IMI occurred in early lactation. Models accounting for the contagious nature of infection fitted better than those not accounting for contagiousness. BTSCC was only associated with prevalence of IMI in early lactation.

CLINICAL RELEVANCE: Reduction of BTSCC in dairy goats may be best achieved by minimising the prevalence and incidence of new IMI in early lactation. Further studies are required to define management factors associated with the between herd, and stage of lactation, effects on prevalence and incidence rate in order to reduce BTSCC throughout lactation.     

Failure of Duddingtonia flagrans to reduce gastrointestinal nematode infections in dairy ewes

A field study was conducted on three Swiss farms to investigate the efficacy of Duddingtonia flagrans against naturally acquired infections of gastrointestinal nematodes in adult dairy sheep. On each farm the ewes were divided into two equal groups. One group received Duddingtonia during a period of 4 months at a daily dose rate of 10(6) chlamydospores per kilogram body weight, the second group acted as controls. At an overall moderate infection level in all farms D. flagrans did not have a significant effect on the observed parasitological parameters with the exception of a significantly reduced herbage infectivity in one farm. In contrast, the results from faecal cultures indicated a mean suppression of larval development during the fungus-feeding period between 82, 89 and 93% on the three farms, respectively. The discrepancy observed between the fungus efficacy in coprocultures and on pasture, which was also observed in several other studies deserves further research.     

Observations on intramammary infections in first calf heifers in early lactation

Intramammary infections and mastitis were monitored on four occasions at three-week intervals in 61 first calf heifers in five dairy herds during the first ten weeks of lactation. Of 940 quarter milk samples examined 65% were classed as negative, 10.4% as positive for mastitis (mainly subclinical), 1.8% as group 3 (infection present but no elevation in somatic cell count) and 22.8% as group 4 (elevated somatic cell count). Seventy-seven percent of the infections detected and identified were those due to coagulase-negative staphylococci, the main species being S. hyicus, S. epidermidis, S. simulans and S. hominis. Other infections detected with Corynebacterium pyogenes (three samples), Escherichia coli (one sample), Micrococcus spp. (one sample), S. aureus (two samples) and Streptococci (non-agalactiae) (seven samples).The geometric mean somatic cell count for 23 quarters infected with coagulase-negative staphylococci was 311 x 10(3) cells / mL compared to 134 x 10(3) cells / mL in noninfected adjacent contralateral quarters. The respective figures for% cell volume in Channel 8 (mainly neutrophils) were 10.6% and 3.5%. There was a highly significant association between herd and the proportion of quarter milk samples in the four mastitis categories.     

Clinical findings and pathological changes in Histophilus ovis infections of sheep

The Gram-negative pleomorphic bacterium Histophilus ovis was incriminated as the cause of natural cases of epididymitis in rams, polyarthritis in lambs, mastitis and abortion in ewes. Epididymitis was sporadic in occurrence, unilateral in distribution and varied from acute to chronic in degree. Polyarthritis affected recently born lambs and resulted in acute lameness and subsequent debility. Mastitis was rare in occurrence, unilateral in distribution, acute and gangrenous in type. Abortion was also rare and manifested by a specific haemorrhagic placentitis. These four conditions were reproduced experimentally. The clinical, pathological and histopathological changes associated with field and experimental cases are described.     

Field trials on the prophylaxis of intramammary infections in pregnant heifers

The study was carried out in 5 farms on 174 pregnant heifers. Clinical examination of the udder and bacteriological tests of quarter secretion were performed between the 8th and 3rd week before parturition, and then the animals were divided into a control group (64 heifers) and 3 experimental groups and immediately treated. A group of 32 experimental heifers was injected once with antioxidants (Vitamin A--600,000 i.u.; Vitamin D3--200,000 i.u.; Vitamin E--1.5 mg/kg b.w., Selenium--0.022 mg/kg b.w., i.m.). The next group (26 heads) was intramammary infused with antibiotic DC product (cloxacillin). Heifers from last experimental group (52) were injected with lysosyme dimer in a single dose of 0.02 mg/kg b.w. Clinical and bacteriological examinations were made during the first week after calving. The presence of bacteria was found in secretion of 22.6-38.9% udder quarters in 56.2-71.2% of pregnant heifers. The number of infected quarters (cows) did not change distinctly in the first week after calving except the lysozyme dimer group, where a decrease by 30% was noted. The percentage of quarters with elevated somatic cell count was higher in antibiotic DC group and closely similar in the other groups. None of examined methods showed an acceptable prophylactic effect. Clinical mastitis cases during first week after parturition were mostly caused by Escherichia coli, Staph. chromogenes, Staph. simulans, Staph. aureus, Staph. hyicus, Str. uberis, Str. acidominimus and Enterococcus faecalis.     

Epidemiology of Streptococcus uberis intramammary infections in a dairy herd.

From 1987 to 1991, almost 36,000 quarter samples of mammary secretion representing 1790 lactations of 510 dairy cows from a research herd were collected for bacteriological examination. The percentage of cows infected with Streptococcus uberis ranged from 12 to 16% of cows/year. S. uberis was isolated from 14.2% of lactations over the 5-year period. The prevalence of S. uberis intramammary infection (IMI) was significantly higher in cows with > or = 4 lactations than in cows with 3 or fewer lactations. Regardless of lactation number, the prevalence of S. uberis was highest before parturition, during early lactation and near drying off. The prevalence of S. uberis infected quarters ranged from 1.3 to 2.3% of quarters/year; the prevalence rate for the 5-year period was 2% of quarters. The quarter prevalence of S. uberis was lowest in cows with < or = 3 lactations, increased significantly with lactation number and was highest in cows with > or = 6 lactations. The percentage of quarters infected with S. uberis varied significantly by year. The majority (95%) of S. uberis IMI were subclinical. The ratio of subclinical IMI to clinical IMI was lowest during early lactation, and increased with days in milk, and with lactation age except for cows in their 5th and 6th lactations. Results of this epidemiological investigation suggest that opportunities exist where suitable control measures could be applied to reduce the impact of S. uberis infections in the dairy herd.     

Treatment of persistent intramammary infections with Streptococcus uberis in dairy cows

A survey was conducted of the prevalence of environmental pathogens, especially Streptococcus uberis, as causes of clinical mastitis in dairy cows. The response of intramammary infections with S uberis to conventional treatment was monitored by taking milk samples for bacteriology and somatic cell counting seven, 14 and 21 days after the treatment. The results showed that 51 per cent of the infections failed to respond, and the odds of cases failing to respond was significantly increased when the individual quarter somatic cell count seven days after the treatment was greater than 201,000 cells/ml. Ninety-six per cent of the suspected S uberis isolates identified by culture were confirmed as S uberis by using the api 20 Strep system. Restriction endonuclease fingerprinting was used to type the strains of S uberis isolated from 75 milk samples from 32 cows. Analysis showed that 96 per cent of the cases of S uberis that failed to respond to conventional treatment were persistent infections with one strain rather than reinfections with different strains. The persistent cases of S uberis were treated further with an extended course of intramammary preparations containing either procaine penicillin with dihydrostreptomycin or cefquinome. There was no significant difference between the cure rates achieved by the two preparations, and 55 per cent of the cases that had failed to respond to conventional treatment responded to the additional treatment.     

Study of intramammary infections in dairy goats from mountainous regions in Italy

Extract

The manufacture of dairy products from the milk of small ruminants presents an opportunity to improve the economics of farming in remote areas such as the mountainous regions in northern Italy. Mastitis, particularly subclinical and chronic, is the most persistent and widespread problem affecting milk quality. Currently, there is a lack of information concerning the most common causal agents of mastitis in dairy goat herds in Italy. This study was undertaken to determine the aetiology and prevalence of intramammary infections (IMI), and to measure somatic cell counts (SCC) of dairy goats in mountainous regions of northern Italy.