Potassium Dynamics in US Coastal Plain Soils

ABSTRACT

Potassium (K) deficiency in crops in southern US Coastal Plain soils has been documented since the l880s. Long-term soil fertility studies such as Alabama’s “Cullars Rotation” experiment (circa 1911) have been conducted with K since 1911. Other Alabama long-term experiments on several Coastal Plain and related Hapludults, Paleudults, and Kandiudults also contain K variable treatments which have been monitored since 1929. Soil test data from these long-term experiments have allowed us to answer some practical questions regarding K dynamics in Coastal Plain soils. Potassium movement through the soil profile is dependent on the soil’s cation exchange capacity (CEC) but relative accumulation is greater in the plow layer regardless of soil CEC. While subsoil K testing may be useful for identifying situations where subsoil K has been depleted, this extra effort and expense is not necessary for most cropping situations. A crop will remove most of its K from the plow layer if it is present in sufficient quantity based on soil test. Crop depletion of plow-layer K to the point where yield may be reduced is gradual and may take 10–15 years or more depending upon soil CEC and initial soil K concentration. Depletion is most rapid in low CEC soils as would be expected. However, soil test K can vary considerably during the course of a crop season with the lowest soil test K concentrations occurring immediately after harvest.     

Histofarcin test for the diagnosis of epizootic lymphangitis in Ethiopia: development, optimisation, and validation in the field

Histofarcin, a skin test antigen for the diagnosis of epizootic lymphangitis, was locally produced from the mycelial form of Histoplasma capsulatum var. farciminosum (HCF) in disease-endemic districts of Ethiopia and tested for its application in the field between April 2002 and May 2003. The test was evaluated using 108 mules, 84 in endemic and 24 in disease-free districts. Microscopic and mycological examinations of clinical lesions were used as the "gold standard" for the validation of the test. The concentration of histofarcin that caused an optimum reaction was 0.2-0.4 mg/mL in a 0.1 mL dose and this was attained 24-48 h post-injection. The sensitivity and specificity of the histofarcin test were 90.3% (CI = 73.1, 97.5) and 69% (95%, CI = 48.1, 84.9%) in disease-endemic districts. On the other hand, specificity was 100% (CI=94.8, 100) in disease-free districts. Positive and negative predictive values of the histofarcin test were 77.78% (95% CI = 60.4, 89.3) and 85.71% (95% CI = 62.6, 96.2), respectively. A marginal substantial agreement (kappa = 0.61, P = 0.0000) was observed between the clinical status and the result of the histofarcin test. A large proportion (31%) of 'false positives' was recorded in endemic districts, which could be due to the pre-clinical stage of the disease. The latter ended in lower specificity and positive predictive value of the test since the true infection status of a 'false positive' could not be known on the basis of clinical features. Therefore, standard test validation procedures including slaughtering and isolation of HCF is required. After proper validation, we conclude that the histofarcin test could play a significant role in detecting early infection, and differentiating of EL from glanders, ulcerative lymphangitis, and sporotrichosis.     

Vaccination of calves with Mycobacteria bovis Bacilli Calmete Guerin (BCG) induced rapid increase in the proportion of peripheral blood γδ T cells

Changes in the proportion of peripheral blood T cell subsets after subcutaneous inoculation of cattle with Mycobacterium bovis Bacille Calmette-Guerin (BCG) were studied. Calves were injected with approximately 8 × 10⁶ BCG bacillus and blood samples collected at weekly intervals for flow-cytometric analyses to determine the proportion of CD4⁺, CD8⁺ and γδ T cells. In addition, whole blood samples were stimulated in vitro with M. bovis purified protein derivative (PPD) and the secreted IFN-γ quantified by ELISA. Results showed cellular and cytokine changes which could be categorized into three phases. The first phase occurred within the first 2 weeks after vaccination involving an increase in proportion of WC1⁺ γδ T cells and a concomitant increase in the secretion of IFN-γ. These two responses peaked at 2 weeks and waned thereafter. The second phase involved an increase in the CD4/CD8 ratio as a result of an increase in the proportion of CD4⁺ T cells between 4 and 6 weeks. The third phase involved a decrease in the CD4/CD8 ratio due to an increase in the proportion of CD8⁺ T cells between 8 and 10 weeks. Surprisingly, the IFN-γ response was associated with changes in the γδ rather than the CD4⁺ or CD8⁺ T cells, suggesting that this cytokine was secreted by γδ-T cells. These results are consistent with the reported ability of γδ T cells to act rapidly and bridging the innate and classically adaptive immune responses.     

Erratum to: A cross-sectional study on bovine tuberculosis in Hawassa town and its surroundings,Southern Ethiopia

Tropical Animal Health and Production -     

Comparison of different testing schemes to increase the detection <Emphasis Type="Italic">Mycobacterium bovis</Emphasis> infection in Ethiopian cattle

Host immune responses to Mycobacterium bovis (M. bovis) infection are variable at the different severity stages of pathology of the disease. In countries like Ethiopia, where routine screening of bovine TB is not undertaken, the use of tests which measure cellular and antibody responses may help for the maximum detection of infection. In the present study, 701 cattle were tested for bovine tuberculosis (BTB) using comparative intradermal tuberculin (CIDT) test, interferon (IFN)-γ test, and lateral flow assay. The apparent prevalence was 32% when all the three tests were used, but varied from 23 to 25% when a pair of tests was used and from 9% to 15% when a single test was used. Agreement was observed between CIDT and IFN-γ tests both at a cut-off >2 mm (Kappa ± standard Error, k ± SE, 0.129 ± 0.045; 95%CI = 0.041,0.216) and a cut-off >4 mm (k ± SE, 0.094 ± 0.044, 95%CI = 0.008,0.179) while no agreement was observed either between CIDT test and lateral flow assay (k ± SE, −0.04 ± 0.033; 95%CI = −0.104,0.024) or between IFN-γ tests and lateral flow assay (k ± SE, −0.031 ± 0.032; 95% CI = −0.093,0.031). Thus, the use of more than one test leads to the detection of the maximum number of infected animals.     

A cross-sectional study on bovine tuberculosis in Hawassa town and its surroundings,Southern Ethiopia

A cross-sectional study was conducted in Hawassa town and its surroundings from October 2007 to May 2008 to estimate the prevalence of bovine tuberculosis (BTB) based on comparative interadermal tuberculin test (CIDT) and abattoir survey. Accordingly, 39 herds comprising 413 cattle were subjected to CIDT, and the herd and individual animal prevalence were 48.7% (19/39) and 11.6% (48/413), respectively. One of the 16 milk samples collected from tuberculin-positive cows was culture positive. The prevalence significantly differed among the age group (P = 0.001) and management system (P = 0.001). Thus, age group over four (OR = 7.9) and animal with poor management system (OR = 4.1) had a higher odds for tuberculin reactivity compared to those with age group under four and cattle with good management system, respectively. Of the total 1,023 cattle subjected to postmortem examination, 11 (1.1%) were found to be positive for gross tuberculous lesions. Larger proportion (50%) of TB lesion was recorded in the respiratory pathway followed by digestive system (28.6%) and prescapular lymph nodes (21.4%). Of 14 tissue specimens collected from the gross lesions, four (28.6%) were positive for histopathological TB lesions. In conclusion, this study revealed the importance of BTB in the study area in particular and the region in general.     

Equine histoplasmosis: Treatment trial in cart horses in Central Ethiopia

Therapeutic effects of Sodium Iodide (NaI), Potassium Iodide (KI), ground berries of "Endod" (Phytolacca dodecandra) and Penstrip were evaluated on 70 cases of equine hitoplasmosis (EH). Response to each treatment was assessed using clinical examination of the lesions. Statistically significant difference (P = 0.0036) in therapeutic effect was observed among the different remedies. Cases treated either with a combination of NaI and Penstrip (F = 6.34, P = 0.004) or "Endod" and Penstrip (F = 3.64, P = 0.031) demonstrated significant response. The difference in response to treatment between early and advanced cases of EH was statistically significant (t = 2.22, P = 0.0148).     

Epidemiology of equine histoplasmosis (epizootic lymphangitis) in carthorses in Ethiopia

A study was conducted between January 2003 and June 2004 on 19,082 carthorses in 28 towns in Ethiopia to investigate the epidemiology of equine histoplasmosis (EH). Clinical and microscopic examinations were used and an overall prevalence of 18.8% (3579/19082) was recorded. Statistically significant (P<0.001) differences was observed in the average prevalence with high, medium, and low prevalence categories. The highest prevalence (39%) was recorded at Mojo while the lowest (0.0%) was recorded at five towns, namely, Agaro, Bokoji, Debre Berhan, Dinsho, and Sagure. The prevalence of EH was not associated (R=0.08, F=0.15, P=0.71) with the mean annual rainfall but was associated (R=0.64, F=11.5, P<0.01) with the average annual temperature. Statistically significant (R=0.57, F=12.34, P<0.01) association was observed between the altitude of the study towns and the prevalence of EH. Moreover, the number of cases of EH increased significantly (R=0.88, F=90.9, P<0.001) with the horse population in the towns. In general, EH was prevalent in hot and humid towns with an altitude ranging from 1500m above sea level (asl) to 2300masl but was nil or low in cold and in dry and windy towns. It was concluded that EH is prevalent in Ethiopia and warrants the initiation of a control strategy.     

Mycobacterium tuberculosis infection in grazing cattle in central Ethiopia

A preliminary study to characterise mycobacteria infecting tuberculous cattle from two different management systems in central Ethiopia was carried out. Approximately 27% of isolates from grazing cattle were Mycobacterium tuberculosis, while cattle in a more intensive-production system were exclusively infected with M. bovis. The practice of local farmers discharging chewed tobacco directly into the mouths of pastured cattle was identified as a potential route of human-to-cattle transmission of M. tuberculosis.     

The influence of cattle breed on susceptibility to bovine tuberculosis in Ethiopia

Bovine tuberculosis in domestic livestock such as cattle is an economically important disease with zoonotic potential, particularly in countries with emerging economies. We discuss the findings of recent epidemiological and immunological studies conducted in Ethiopia on host susceptibility differences between native zebu and the exotic Holstein-Friesian cattle that are increasingly part of the Ethiopian National herd, due to the drive to increase milk yields. These findings support the hypothesis that native Zebu cattle are more resistant to bovine tuberculosis. We also summarise the results of experimental infections that support the epidemiological data, and of laboratory experiments that suggest a role for the innate immune response, and in particular interleukin-6, in the outcome of bovine tuberculosis infection.