A cost-benefit model comparing the California Milk Cell Test and Milk Electrical ResistanceTest

The indirect effects of mastitis treatment are often overlooked in cost-benefit analyses, but it may be beneficial for the dairy industry to consider them. The cost of mastitis treatment may increase when the duration of intra-mammary infections are prolonged due to misdiagnosis of host-adapted mastitis. Laboratory diagnosis of mastitis can be costly and time consuming, therefore cow-side tests such as the California Milk Cell Test (CMCT) and Milk Electrical Resistance (MER) need to be utilised to their full potential. The aim of this study was to determine the relative benefit of using these two tests separately and in parallel. This was done using a partial-budget analysis and a cost-benefit model to estimate the benefits and costs of each respective test and the parallel combination thereof. Quarter milk samples (n = 1860) were taken from eight different dairy herds in South Africa. Milk samples were evaluated by means of the CMCT, hand-held MER meter and cyto-microbiological laboratory analysis. After determining the most appropriate cut-off points for the two cow-side tests, the sensitivity and specificity of the CMCT (Se = 1.00, Sp = 0.66), MER (Se = 0.92, Sp = 0.62) and the tests done in parallel (Se = 1.00, Sp = 0.87) were calculated. The input data that were used for partial-budget analysis and in the cost-benefit model were based on South African figures at the time of the study, and on literature. The total estimated financial benefit of correct diagnosis of host-adapted mastitis per cow for the CMCT, MER and the tests done in parallel was R898.73, R518.70 and R1064.67 respectively. This involved taking the expected benefit of a correct test result per cow, the expected cost of an error per cow and the cost of the test into account. The CMCT was shown to be 11% more beneficial than the MER test, whilst using the tests in parallel was shown to be the most beneficial method for evaluating the mastitis-control programme. Therefore, it is recommended that the combined tests should be used strategically in practice to monitor udder health and promote a pro-active udder health approach when dealing with host-adapted pathogens.Scan this QR code with your smart phone or mobile device to read online.J.K. drafted the manuscript and critically revised it, formatted and edited the manuscript, was involved in the data analysis, calculating the sensitivity and specificity, as well as assisting in calculating the cost-benefit model and determining the model inputs for the partial-budget analysis. I.M.P. assisted in collection of aseptic milk samples and performing of cowside tests, assisted with model inputs, reviewing the technical aspects of the manuscript. I.A.M. was involved in calculating the cost-benefit model, doing all the excel calculations, calculating the model inputs and technical editing of the article. T.J.v.d.S. was mainly involved in collecting of aseptic samples and performing of all the cow-side tests in the dairy, as well as in editing the manuscript.http://www.ojvr.orgam2013ab201

Comparing effects of freezing at -196 °C and -20 °C on the viability of mastitis pathogens

The aim of this study was to compare the effects of cryopreservation at approximately -196 °C in liquid nitrogen (N) and freezing at approximately -20 °C in a freezer, on the viability and survival of eight different mastitogenic bacteria inoculated in milk. Bacteria were frozen at approximately -20 °C in a freezer and cryopreserved at approximately -196 °C in liquid nitrogen. An effective preservation method was needed for follow-up samples from cows identified in the South African National Milk Recording Scheme (NMRS) with somatic cell counts above 250 000 cells/mL milk. The organisation responsible for sample collection of the NMRS milk samples also provides producers with liquid nitrogen for their semen flasks at the collection sites. This existing mode of storage and transport could therefore be utilised. Ten samples of each organism were thawed and cultured bi-weekly until week 18 for both temperature treatments. An additional sampling was performed at week 30 for samples frozen at approximately -20 °C. Freezing and cryopreservation did not impair subsequent isolation of Streptococcus dysgalactiae, Streptococcus uberis, Enterococcus faecalis, Staphylococcus aureus (STH) (phage type lytic group III) or Sta. aureus (STA) (phage typed, other than lytic group III). Survival was indicated by the isolation of bacteria from samples, and viability by the strength of growth of the bacteria isolated. The survival of Streptococcus agalactiae decreased after week 12 and Escherichia coli after week 16 of freezing, but both organisms survived under cryogenic preservation until week 18. Coagulase-negative staphylococci survived until week 18 for both freezing and cryogenic preservation. Both storage methods could thus contribute to the improvement of a pro-active approach towards udder health management in South African dairy herds.I.M.P. (University of Pretoria) was the project leader. I.M.P. (University of Pretoria), J.C.W. (University of Pretoria) and T.J.v.d.S. (University of Pretoria) were responsible for experimental and project design. N.M.I. (Herd Husbandry Help CC) assisted with the storage of samples in liquid nitrogen (-196 ºC) by making facilities available. S.E. (University of Pretoria) assisted with data capturing. J.K. (University of Pretoria) and I.M.P. (University of Pretoria) were responsible for the literature review, the writing-up of the article, and G.T.F. (University of Pretoria) assisted with data utilisation and statistical analysis.http://www.ojvr.orgab201

Trends in udder health and emerging mastitogenic pathogens in South African dairy herds

The aim of this study was to retrospectively analyse the results of milk samples obtained from South African dairy herds during the period 1996 to April 2007 in order to identify possible trends in isolates of microorganisms and their pathogenicity under field conditions. Milk samples were obtained from 7 of the 9 provinces in South Africa where there are low numbers of dairy cows. Although there is scientific limitation to a country wide survey, such as the variation in herd size, management skills, parity, milk yield, milking frequency and other parameters, the size of this database helps to give a fair indication of general udder health in South Africa. Cytology and routine bacteriology were performed on 379 000 milk samples of lactating cows and bacteriology on 11 946 samples from non-lactating cows. According to the results obtained, mastitis did not decrease in South Africa over the test period. The prevalence of mastitis and teat canal infection was lowest in 2002. Mastitis and teat canal infection increased from 2002 to 2006 from 8.1 % and 24.1 % to 15.4 and 30.0 % respectively. The percentage of mastitogenic pathogens isolated from cows over these years also varied. Previously unknown or almost eradicated mastitogenic pathogens such as αβ haemolytic Staphylococcus aureus which is thought to be of human origin, Streptococcus agalactiae and Enterococcus canis were responsible for numerous mastitis outbreaks seen in the test samples. Coagulase-negative staphylococci were the most frequently isolated bacteria in milk samples from both lactating and dry cows, followed by Staphylococcus aureus and Streptococcus agalactiae. Although Staphylococcus aureus remained the principal mastitogenic pathogen in South Africa, owing to its chronic nature and resultant economic losses, most cases of mastitis were caused by coagulase-negative staphylococci. This finding increases the importance of coagulase-negative staphylococci (formerly described as a minor pathogen) significantly. Isolations of Streptococcus agalactiae peaked between 2000 and 2005 and decreased again by 2007. Coagulase-negative staphylococcal isolates increased from 2002 and were still on the increase in 2007. Streptococcus agalactiae, Streptococcus uberis and Enterococcus canis were isolated more frequently from milk samples of lactating cows compared with dry cows, while Enterococcus faecalis was isolated more frequently from dry cow samples

Intramammary antibiotic withdrawal periods for dairy goats compared to those for dairy cattle

This study investigated the withdrawal periods (WP) of two intramammary antibiotics Cloxamast LC (Intervet SA) and Spectrazol Milking Cow (Schering-Plough Animal Health) in dairy goats and compared them to those recommended for use in cattle. The WP for Cloxamast LC, measured by the Thermo Resistant Inhibitory Substances (TRIS) test, was 60 h in composite samples, 56 h in udder half samples, and the dye was visible for up to 56 h. The WP was significantly shorter than the 72 h recommended WP for use in cattle. It was however significantly longer when the 24 h safety margin (48 h) was subtracted from the recommended WP for cattle. For Spectrazol Milking Cow the antibiotics could be detected by the TRIS test for 61 h in composite samples and 59 h in udder half samples. This did not differ significantly from the recommended 60 h WP for cattle. However, it was significantly longer than that recommended for use in cattle without the 24 h safety margin. There was no significant difference in WP between infected and non-infected udder halves, while there was a weak positive correlation between WP and stage of lactation (R2 = 0.253). There was a moderate positive correlation (R2 = 0.583) between the TRIS test and the presence of dye in milk in udder half samples and between WP in both udder half and composite milk samples (R2 = 0.456). Weak to moderate positive correlations were present between milk yield and the WP in both udder half (R2 = 0.414) and composite (R2 = 0.262) milk samples. Significant differences (P < 0.001) were also observed between the milk yield of udder halves with and without palpable udder damage and between samples that tested TRIS positive and negative on both composite (P = 0.008) and udder half samples (P < 0.001). There was no significant difference between the milk yield of samples with or without dye. There was a significant difference in milk yield between infected and non-infected udder halves (P = 0.054) and a weak negative correlation between milk yield and stage of lactation (R2 = –0.379)

Value of tests for evaluating udder health in dairy goats : somatic cell counts, California Milk Cell Test and electrical conductivity

The value of electric conductivity (EC), California Milk Cell Test (CMCT) and somatic cell count (SCC) as diagnostic tools was investigated in dairy goats. Conductivity colour reading correlated with SCC. Milk samples with conductivity colour red had significantly higher SCC than those with conductivity colours green and orange (P < 0.001). There were moderate positive correlations between CMCT (R2 = 0.470), and conductivity score and CMCT and conductivity colour readings (R2 = 0.597). Conductivity scores were significantly (P < 0.001) higher during and after intra-mammary treatment with Cloxamast LC and conductivity colours were significantly different between treatment and control groups (P < 0.001). There was a weak positive correlation between conductivity colour and stage of lactation (R2 = 0.317) and a moderately positive correlation between conductivity score and stage of lactation (R2 = 0.523). A moderately negative correlation was shown between milk yield and conductivity score (R2 = –0.426) and between milk yield and conductivity colour (R2 = –0.433). Moderate positive correlations were present between CMCT and SCC (R2 = 0.689) and between CMCT and stage of lactation (R2 = 0.459). CMCT ratings were significantly different (P < 0.001) for the intramammary treatment groups. CMCT ratings for infected and non-infected udder halves (P = 0.008) were significantly different; as were those for infected and non-infected udder halves and for left and right udder halves separately (P = 0.010). CMCT ratings for milk samples with SCC above and below 750 x 103 cells per mℓ were significantly different (P < 0.001) as well as for milk from treated and control udder halves with SCC below or above 750 x 103 cells per mℓ (P < 0.001). CMCT was found to be more accurate for indicating the absence of mastitis than for diagnosing it. There were significant differences in log SCC between treatment and control groups, during and after treatment. Infected udder halves had significantly higher log SCC than non-infected udder halves before and after treatment, but not during treatment. There was a moderate positive correlation between stage of lactation and SCC (R2 = 0.438)

Intramammary infection rate during the dry period in cows that received blanket dry cow therapy : efficacy of 6 different dry-cow intra-mammary antimicrobial products

The objectives of this study were to compare the efficacy of 6 different dry-cow intramammary antimicrobial products for the treatment and prevention of mastitis during the dry period in a well-managed high producing Friesland dairy herd, and the influence of treatment on the somatic cell count (SCC) of cows during early lactation. One of 6 dry-cow intramammary antimicrobial products was randomly allocated to 162 cows due for drying off over a period of 14 months. All cows were sampled twice prior to drying off, and twice after calving for the determination of SCC and presence of microorganisms. The quarter prevalence of pathogens at drying off and post-calving, the overall quarter cure rate and the rate of new intramammary infections occurring during the dry period were determined. The overall quarter prevalence of intramammary infections (IMIs) at drying off was 29.78 % and after calving 22.22 %. There was a statistically significant difference (P < 0.05) between the prevalence of major and minor pathogens at drying off (7.87 % and 21.91 %) and at calving (4.47 % and 17.75 %). The most prevalent pathogens isolated at drying off (21.14 %) and at calving (16.98 %) were coagulase-negative staphylococci (CNS). The quarter cure rate during the dry period was 83.94 %. The cure rate for the major pathogens (98%) was significantly better (P < 0.05) than that for minor pathogens (78.9 %). The overall quarter cure rate varied from 72.3 % to 93.9 % for the various products. The rate of new quarter infections during the dry period was 17.44 % with a significant difference (P<0.05), between the prevalence of new quarter infections with major (4.32 %) and minor pathogens (13.12 %). CNS was the most prevalent pathogen causing new quarter infections (12.34 %) and the rate o f new quarter infections varied from 13.4 % to 24.1 % for the various products. It is concluded that there is a difference in efficacy between antimicrobial intramammary dry-cow products in their ability to cure and prevent new IMIs during the dry period. Dry-cow products are mainly formulated for efficacy against Gram-positive cocci, while providing no or little protection against Gram-negative bacteria. Therapeutic levels may persist for only 14 to 28 days into the dry period and fail to protect the udder during the last trimester. Dry-cow therapy should, however, always form part of a holistic approach to the dry period which also considers cow factors, dry-cow management, microorganisms and the environment of the dry cow