Antimicrobial usage and risk of retreatment for mild to moderate clinical mastitis cases on dairy farms following on-farm bacterial culture and selective therapy

AIMS: To assess antimicrobial usage for treatment of mild to moderate clinical mastitis, and risk of retreatment, following implementation of an on-farm bacterial culture system and selective therapy based on culture results, and to assess compliance with treatment decision tree protocols and the level of agreement between results from on-farm culture and laboratory-based microbiology methods.

MATERIALS AND METHODS: Herdowners from seven dairy herds were asked to collect milk samples from cases of mild to moderate clinical mastitis between July 2015 and May 2016. All samples were cultured on-farm using a commercially available selective media and were also submitted for laboratory-based culture. Within sequential pairs of cows with mastitis, half were assigned to be treated without regard to culture results (Blanket group), and half were treated based on the on-farm culture results (Selective group) according to decision tree diagrams provided to the farmers. Culture results, treatments, and retreatments for clinical mastitis were recorded. The sum of the daily doses of antimicrobials used per cow, the number of retreatments and interval to first retreatment were compared between treatment groups.

RESULTS: The geometric mean sum of daily doses for quarters assigned to the Selective (1.72 (95% CI=1.55–1.90)) group was lower than for the Blanket (2.38 (95% CI=2.17–2.60)) group (p=0.005). The percentage of cows retreated for clinical mastitis did not differ between the Selective (21.7 (95% CI=10.5–25.9)%) and Blanket (26.1 (95% CI=20.9–31.3)%) groups (p=0.13), and there was no difference between groups in the hazard that cows would be retreated within 60 days of enrolment (hazard ratio=0.82 (95% CI=0.39–1.69); p=0.59). Compliance with the treatment protocols was higher amongst quarters assigned to the Selective (199/233; 85.4%) compared with the Blanket (171/249; 68.7%) group (p<0.001), and varied between farms from 64–94%. The overall agreement between results from on-farm and laboratory culture was 188/331 (56.9%; kappa=0.31; p<0.001), but varied between farms from 44.7–88.2% (p<0.001).

CONCLUSIONS: Use of on-farm culture with selective antimicrobial therapy resulted in approximately 25% lower antimicrobial usage, but was not associated with an increase in the proportion of cows retreated for clinical mastitis.

CLINICAL RELEVANCE: This study has demonstrated that on-farm culture and selective therapy based on culture results can be implemented on-farm. However, farms varied in their implementation of both the treatment protocols and microbiology procedures. Where such systems are to be used on-farm, specific training and on-going monitoring is required.     

A field trial of infrared thermography as a non-invasive diagnostic tool for early detection of digital dermatitis in dairy cows

Infrared thermography (IRT) was used to detect digital dermatitis (DD) prior to routine claw trimming. A total of 1192 IRT observations were collected from 149 cows on eight farms. All cows were housed in tie-stalls. The maximal surface temperatures of the coronary band (CB) region and skin (S) of the fore and rear feet (mean value of the maximal surface temperatures of both digits for each foot separately, CB_max and S_max) were assessed. Grouping was performed at the foot level (presence of DD, n = 99; absence, n = 304), or at the cow level (all four feet healthy, n = 24) or where there was at least one DD lesion on the rear feet, n = 37). For individual cows (n = 61), IRT temperature difference was determined by subtracting the mean sum of CB_max and S_max of the rear feet from that of the fore feet.Feet with DD had higher CB_max and S_max (P < 0.001) than healthy feet. S_max was significantly higher in feet with infectious DD lesions (M-stage: M2 + M4; n = 15) than in those with non-infectious M-lesions (M1 + M3; n = 84) (P = 0.03), but this was not the case for CB_max (P = 0.12). At the cow level, an optimal cut-off value for detecting DD of 0.99 °C (IRT temperature difference between rear and front feet) yielded a sensitivity of 89.1% and a specificity of 66.6%. The results indicate that IRT may be a useful non-invasive diagnostic tool to screen for the presence of DD in dairy cows by measuring CB_max and S_max.     

A retrospective study of the aetiology and temporal distribution of bovine clinical mastitis in smallholder dairy herds in the Dar es Salaam region of Tanzania

A 31-year record-based retrospective study was carried out to determine the aetiology and temporal distribution of bovine clinical mastitis in smallholder dairy herds in the Dar es Salaam region of Tanzania over the period November 1971-December 2002. Laboratory information on 1964 quarter samples from 1365 cows in 281 smallholder dairy herds were retrieved, compiled and studied. Eighty-eight percent of the quarter samples were culture-positive and the predominant mastitis pathogens isolated were Staphylococcus aureus (25.7%), Streptococcus agalactiae (15.4%), Klebsiella pneumoniae (14.3%) and Escherichia coli (14.1%). Other isolates included Pseudomonas aeruginosa (7.5%), Streptococcus dysgalactiae (5.2%) and Streptococcus uberis (4.2%). Contagious mastitis pathogens were isolated from 45.6% of the culture-positive samples, whereas environmental and miscellaneous pathogens were isolated from 48.2% and 5.7%, respectively. Thirty percent of the miscellaneous mastitis pathogens were Candida species. The results demonstrate a steady increase in clinical Candida albicans mastitis. The prevalence of Candida albicans has increased from 1% in 1971 to 17.0% in November 2002. Conversely, despite some fluctuations, the prevalence of Staphylococcus aureus, Streptococcus agalactiae, E. coli and K. pneumoniae remain above 10%. The possible risk factors for these observations are discussed.     

Comparison of models for genetic evaluation of survival traits in dairy cattle: a simulation study.

Three models for the analysis of functional survival data in dairy cattle were compared using stochastic simulation. The simulated phenotype for survival was defined as a month after the first calving (from 1 to 100) in which a cow was involuntarily removed from the herd. Parameters for simulation were based on survival data of the Canadian Jersey population. Three different levels of heritability of survival (0.100, 0.050 and 0.025) and two levels of numbers of females per generation (2000 or 4000) were considered in the simulation. Twenty generations of random mating and selection (on a second trait, uncorrelated with survival) with 20 replicates were simulated for each scenario. Sires were evaluated for survival of their daughters by three models: proportional hazard (PH), linear multiple-trait (MT), and random regression (RR) animal models. Different models gave different ranking of sires with respect to survival of their daughters. Correlations between true and estimated breeding values for survival to five different points in a cow's lifetime after the first calving (120 and 240 days in milk after first, second, third and fourth calving) favoured the PH model, followed by the RR model evaluations. Rankings of models were independent of the heritability level, female population size and sire progeny group size (20 or 100). The RR model, however, showed a slight superiority over MT and PH models in predicting the proportion of sire's daughters that survived to the five different end-points after the first calving.     

Randomized clinical trial to evaluate the effectiveness of enrofloxacin as a second‐line antibiotic for treatment of acute Escherichia coli mastitis

The objective of the present study was to evaluate the effectiveness of enrofloxacin (ERFX) as a second‐line antibiotic for treatment of acute Escherichia coli (E. coli) mastitis. Forty‐two cows with naturally occurring acute E. coli mastitis were enrolled. On the first day of treatment (day 0), empirically selected antibiotics (oxytetracycline: n = 32, kanamycin: n = 10) were administered. Although systemic signs improved in 10 cows (first‐line group), the signs remained unchanged or worsened in 32 cows on day 1, including two cows that were found dead. The 30 surviving cows were randomly assigned to second‐line groups constituting an ERFX group (n = 19) or a control group (n = 11) that was treated with other antibiotics. Response to each treatment was evaluated by measuring clinical signs from day 0 to day 3, subsequent quarter milk recovery, and the 60‐day survival rate. Appetite on day 3 was significantly better in the ERFX group compared to the control group. No significant differences were observed in the 60‐day survival rate or the subsequent milk recovery between the ERFX group and the control group. Thus, the use of ERFX as a second‐line antibiotic for the treatment of acute E. coli mastitis could induce a rapid appetite recovery.     

Differentiating between analytical and diagnostic performance evaluation with a focus on the method comparison study and identification of bias

Prior to introduction of a new method to the diagnostic laboratory, analytical performance must be validated to ensure operation within the manufacturer's specifications and/or within predetermined quality requirements. In addition, the new method may require diagnostic performance assessment to ensure it differentiates between diseased and nondiseased individuals as intended. These 2 phases of assessment, while complementary, are not equivalent and require a different set of experiments, statistical analyses, and interpretation. Studies of analytical performance typically include a method comparison experiment, the purpose of which is to identify bias (inaccuracy) of the “test” (or “index”) method (new method) relative to a “comparative method” (established method). Analysis of method comparison data is facilitated by commercial software programs that present the statistical significance of identified bias; however, the clinical relevance of any bias also should be considered. Studies of diagnostic performance should not be pursued until analytical performance is fully characterized and may not be required for well‐established tests or for those for which results are nonspecific (ie, not referable to a specific disease or condition). Diagnostic performance assessment may include assessment of sensitivity, specificity, predictive values, odds ratios, and/or likelihood ratios. The purpose of this review is to clarify differences between the assessment of analytical and diagnostic performance, and to explore the method comparison study and bias assessment from a perspective not addressed in prior veterinary articles.     

Economic evaluation of artificial insemination of sex‐sorted semen on a Brown Swiss dairy farm—A case study

Artificial insemination using sex‐sorted semen is employed to efficiently increase the number of female dairy calves born. Previous studies have determined that using sex‐sorted semen is beneficial to improve the management, but the mechanism by which it increases cattle numbers through objective indices of breeding remains unclear. This study focused on a Brown Swiss cattle herd in which frozen female sex‐sorted semen was systematically employed to increase the number of cattle. We analyzed the correlation between the increase in the number of cattle and the screening accuracy of sex‐sorted semen, measuring indices such as pregnancy rate and birth rate of female calves. Study revealed that: (1) production cost for female calves is influenced by the pregnancy rate, rate of female calves, and using sex‐sorted semen is less expensive than using nonsorted semen; (2) improvements in screening accuracy nearly doubled the number of cows and tripled the number of heifers in 5 years; and (3) use of sex‐sorted semen improved milk quality. The pregnancy rate was lower when sex‐sorted semen was used, but the birth rate of heifers was improved. Results suggest that artificial insemination using sex‐sorted semen is beneficial because it economically produces offspring to increase the herd.     

Effects of Moringa oleifera leaves as a substitute for alfalfa meal on nutrient digestibility,growth performance,carcass trait,meat quality,antioxidant capacity and biochemical parameters of rabbits

This contribution reports the effects of Moringa oleifera leaves (MOLs) meal on the growth performances, nutrient digestibility, carcass trait, meat quality, antioxidant capacity and biochemical parameters of growing New Zealand white rabbits. The MOL was substituted for alfalfa meal at levels of 0, 10%, 20% and 30% to obtain respective diets MOL0, MOL10, MOL20 and MOL30. Each treatment was replicated five times with 10 rabbits per replicate. Results showed the average daily weight gain (ADWG) and feed conversion ratio (FCR) of rabbits fed MOL20 diet were significantly better (p < 0.05) than those of other three dietary groups. Liver and spleen index of rabbits fed MOL20 and MOL30 diets was significantly higher (p < 0.05) than that of the groups fed with lower M. oleifera leaves (MOL0, MOL10). The meat drip loss of rabbits fed with diet MOL10 was significantly lower (p < 0.05) than that of rabbits fed other diets. All rabbits fed MOL dietary groups had lower (p < 0.05) shear force of longissimus dorsi than the group without M. oleifera leaves. No significant differences were found in the digestibility of crude fibre (CF), crude fat (EE), ash, crude protein (CP) and nitrogen‐free extract (NFE) among the dietary groups. Moringa oleifera leaves also have a significant impact on serum albumin (ALB), low‐density lipoprotein cholesterol (LDLC), triiodothyroxine (T₃) and tetraiodothyroxine (T₄) values and the activity of superoxide dismutase (SOD) and catalase (CAT) in serum and liver. The results indicated that M. oleifera leaves could be developed as a good feed source, and it not only could substitute for alfalfa meal well but also has a significant effect on growth performance, meat quality, antioxidant and biochemical parameters of rabbits.     

Standing low‐field MRI of the equine proximal metacarpal/metatarsal region is considered useful for diagnosing primary bone pathology and makes a positive contribution to case management: A prospective survey study

High‐field MRI of the proximal metacarpal/metatarsal region has been associated with great diagnostic potential and clinical reports of standing low‐field MRI of the forelimb suggest the same. To better understand diagnostic outcomes with standing low‐field MRI of the proximal suspensory region, a prospective survey study was conducted and users of a widely available system questioned on their experience, operating procedures, and interpretation of standing low‐field MRI findings. Response data included scores on a modified Likert scale from which weighted ratings were calculated for statistical analyses. Depending on the question, responses were obtained from 17 to 29 of the 38 invited facilities. Users indicated that standing low‐field MRI was most frequently performed in the face of equivocal diagnostic findings; compared to Sports horses, general purpose riding horses were thought less likely to have detectable abnormalities and standing low‐field MRI was rated most useful for the detection of primary bone pathology in the proximal metacarpal region. Standing low‐field MRI signal change involving both the suspensory ligament and adjacent bone concurrently was rated most relevant and abnormalities solely affecting the muscle/adipose tissue bundles least relevant for diagnosing suspensory ligament injury. Transverse scans and in decreasing order T1‐weighted gradient echo, short‐tau inversion recovery FSE, T2*‐weighted gradient echo, and T2‐weighted FSE sequences were most frequently acquired and judged most useful by the majority of users experienced in imaging of the target area. This survey supports the relevant impact of standing low‐field MRI on clinical case management, particularly in the context of imaging the proximal metacarpal region.