Effects of a Cover Crop on Splash Dispersal of Colletotrichum acutatum Conidia

ABSTRACT A rain simulator, with generated rains of 11 and 30 mm/h, was used to determine the effect of a cover crop or intercrop on the splash dispersal of Colletotrichum acutatum conidia. Dispersal through sudangrass, which can be used as a 'living mulch', was tested at two planting densities (140 or 280 kg/ha) and two heights (5 and 20 cm) and compared with a control consisting of a bare soil. Dispersal of C. acutatum conidia was assessed by counting colonies formed from spore-bearing splash droplets deposited in sheltered petri plates containing a selective medium. Both a cover crop and rain intensity significantly affected splash dispersal as measured by the interpolated total number of colonies (denoted by Sigma) from 0 to 72 cm from the inoculum source and in a time span of 61 min of generated rain (P < 0.001). However, there was no significant interaction of cover crop and intensity (P > 0.90). Dispersal with a 30-mm/h rain was higher than dispersal with a 11-mm/h rain, and presence of a cover crop significantly reduced dispersal compared with bare soil (P < 0.001). Of the treatments with sudangrass, cover crop planting density did not affect dispersal overall, but there was greater spore dispersal with the taller sudangrass at the higher planting density, due in part to the higher rate of water splashing with the tall grass compared with the short grass. Spore deposition in the petri plates could be functionally related to distance and time using a diffusion-type model, and parameter estimates could be used to explain the effects of cover crop on Sigma. Although the relationship between cover crop properties and splash dispersal is complex, results show the potential beneficial effects of the cover crop on disease management.     

Epidemiology and pathogenesis of Mycobacterium bovis infection of red deer (Cervus elaphus) in New Zealand

AIMS: This study was initiated to investigate aspects of the epidemiology, pathogenesis and transmission of tuberculosis in wild red deer, with the aim of determining whether this species may be considered a reservoir host of Mycobacterium bovis in New Zealand. METHOD: One hundred and six wild red deer (Cervus elaphus) carcasses from the Castlepoint and Hauhungaroa Range areas, which are endemic for bovine tuberculosis, were examined for the presence of M. bovis infection. Samples were also examined from 46 skin test-positive farmed deer killed at two deer slaughter premises. Where possible, a standard set of tissues and excretion site samples was collected for mycobacteriological examination. RESULTS: Fifty-eight infected deer were identified, and of these 28% showed no gross lesions. The prevalence of tuberculosis confirmed by culture in the wild deer was 32%. Only one of 18 deer younger than 1 year was infected. Mature deer (>2 years) were 12 times more likely to be infected than those under 1 year of age. Infected older deer were less likely to show typical gross lesions than younger animals. Mycobacterium bovis was isolated from the oropharyngeal tonsil of 34 of 56 (61%) of the infected deer, and this was the most commonly infected site. Gross lesions were found in 18 of the 34 infected tonsils and only one of these showed a purulent tonsillitis. Mycobacterium bovis was recovered from four of 53 nasopharyngeal tonsils, four of 53 oropharyngeal swabs, one of 53 tracheal and nasal swabs, and one of 46 faecal samples, but not from any urine specimens. CONCLUSION: These findings suggest that significant bacillary excretion from infected deer was uncommon, and is more likely to occur in severely affected animals. This study has confirmed the importance of mucosa-associated lymphoid tissues (MALT), particularly the oropharyngeal tonsil, in the pathogenesis of tuberculosis in deer. The findings justify investigation of the hypotheses that the prevalence of tuberculosis in wild deer in New Zealand is high due to transmission of infection from possums, and that in the absence of an infected possum population, the prevalence of tuberculosis in deer is likely to be low, and spatially patchy. CLINICAL RELEVANCE: The results suggest that about one quarter of infected deer show no detectable gross lesions. This implies that many infected carcasses may enter the food chain unrecognised and that the estimated sensitivity and specificity of diagnostic tests may be erroneous if there is a difference in test performance between those conducted on deer with or without gross lesions. Diagnostic sensitivity following slaughter may be improved by routine culture of oropharyngeal tonsils and careful examination of lungs for adhesions and small subpleural tubercles.     

Selecting linear-score distributions for modelling milk-culture results

The data for this cross-sectional retrospective study are from surveys of 65 dairy-cattle herds in central New York, USA sampled between February, 1993 and March, 1995. The objective was to identify probability distributions of logarithmically transformed somatic-cell counts (linear score) for use in a simulation model of mastitis and milk quality. Probability density functions were estimated using maximum-likelihood estimators for the linear score of individual-cow compositemilk samples culture negative and culture positive for the pathogens Streptococcus agalactiae, Streptococcus non-agalactiae, Staphylococcus aureus, and coagulase-negative staphylococci for the complete dataset and by bulk-tank somatic-cell count group (< 500 000, ≥ 500 000 SCC/ml). Based on the rankings of three goodness-of-fit tests (Anderson-Darling, Kolmogorov-Smirnov and x²), the Weibull distribution (among the three top-ranking distributions for 14 out of 15 cases) may be used to model the individual-cow linear-score response by culture-result-specific bulk-tank somatic-cell count group. A β distribution was among the three top-ranking distributions for nine out of 15 culture-result-specific bulk-tank somatic-cell count groups and has a logical relationship to linear score because it is defined on a fixed interval. On the other hand, the normal distribution had a poorer fit than the Weibull and at least two other distributions for all culture negative and coagulase-negative staphylococci samples. We do not assume that the underlying biological processes are fully explained by either Weibull or β distribution—but modelling the linear score for the above culture results with these distributions provided an adequate fit to the survey data, reduced the need for two-sided truncation that open intervals needed, and had errors that did not appear to be systematically positive or negative.     

Essential Fatty Acid Supplementation In The Treatment Of Canine Atopy: A Preliminary Study

Abstract— In an open, uncontrolled study, 10 dogs with atopy were given evening primrose oil (EPO) (5ml/10kg/day) over a period of 9 weeks. During the first three weeks pruritus, scaling and oedema worsened but erythema and coat condition tended to improve. Subsequently all these parameters tended to improve. The effect on oedema was significant (p < 0.05). Eight of these dogs and two others were then given a 4:1 mixture of EPO and marine fish oil for 9 weeks. Although further reductions in scale and improvements in coat condition were marked in some animals, no significant changes occurred. Alterations in the plasma phospholipid essential fatty acid levels reflected the compositions of the two supplements. These findings suggest that EPO can ameliorate of atopy in dogs. This mirrors observations obtained in studies of human atopic eczema. Résumé— Dans une étude ouverte, sans lot témoin, 10 chiens souffrant d'atopie ont reçu de l'huile d'onagre (5 ml/10 kg/jour) pendant une période de 9 semaines. Pendant les 3 premières semaines, le prurit, le squamosis et l'oedème se sont aggravés mais, l'érythème et l'aspect du poil tendaient à s'améliorer. Enfin tous ces parametres tendaient à s'améliorer. L'effet sur l'érythème a été significatif (p < 0.05). Huit de ces chiens et deux autres ont alors reçu un mélange (4:1) d'huile d'onagre et d'huile de poisson de mer pendant 9 semaines. Bien qu'ultérieurement la diminution du squamosis et l'amélioration de l'état de la fourrure aient été manifestes chez certains animaux, il n'y eut pas de changement significatif. Les modifications des taux d'acides gras essentiels des phospholipides plasmatiques ont reflété la composition des deux supplémentations. Ces observations suggèrent que l'huile d'onagre peut apporter une amélioration de l'atopie canine. Cela reflète certains résultats observés lors d'études sur l'eczéma atopique de l'homme. Zusammenfassung— In einer offenen, nicht kontrollierten Untersuchung wurde 10 Hunden mit Atopie Nachtkerzenöl (EPO) in einer Dosierung von 5 ml/10 kg/Tag über einen Zeitraum von 9 Wochen verabreicht. Während der ersten 3 Wochen verschlimmerten sich Pruritus, Schuppenbildung und Ödeme, während Erytheme und Fellzustand eher eine Tendenz zur Besserung zeigten. Danach besserten sich alle diese Parameter. Die Wirkung auf Erytheme war signifikant (p < 0.05). Acht dieser Hunde und zwei andere erhielten 9 Wochen lang Nachtkerzenöl und Seefischöl in einer Mischung von 4:1 im Anschlufl an diese Untersuchung. Obwohl eine weitere Verminderung der Schuppenbildung und eine Vorbesserung der Fellqualität bei einigen Tieren festgestellt wurden, waren diese Veränderungen nicht signifikant. Die Veränderungen der essentiellen phospholipiden Fettsäuren im Plasma spiegeln die Zusammensetzung der beiden verabreichten Öle wieder. Diese Befunde weisen darauf hin, daß die Atopie des Hundes durch EPO gebessert werden kann. Dies entspricht auch Beobachtungen bei Untersuchungen des atopischen Exzems des Menschen.     

Culture conditions for blastogenic responses of bovine mammary mononuclear cells

Several experimental parameters were examined to determine optimal conditions for proliferative responses of mammary mononuclear cells (MMC) obtained from six nonlactating dairy cows. These parameters were: pre-incubation of cells in medium prior to assay, mitogen concentration, assay incubation time, and type of culture medium. Response variables included viability of cells and the rate of proliferation as assessed by tritiated thymidine incorporation. Pre-incubation of cells in medium had no effect on the proliferative response of MMC. Whereas Concanavalin A (ConA; 3.3 or 6.6 micrograms/ml) and phytohemagglutinin (PHA; 1, 5, 10 micrograms/ml) did stimulate proliferation of MMC, the higher doses did not stimulate greater proliferation than the lower doses of mitogens. The greatest mitogenic response was obtained on days 2 and 3 of incubation. Proliferative responses were significantly higher at all mitogen levels tested in a 50-50 mixture of Rosewell Park Memorial Institute medium 1640 and Liebovitz-15 medium (RPMI/L-15) than in RPMI alone. Viability of MMC was also significantly higher in the RPMI/L-15 medium. To test whether the significant effect of media on blastogenesis was specific for mononuclear cells from the bovine mammary gland, peripheral blood lymphocytes (PBL) from four dairy cows were cultured with ConA and PHA in a mitogen assay in both RPMI and RPMI/L-15. Viability was measured on day of collection and on all culture days. PBL were stimulated equally in both media. PBL viability decreased significantly on day 1 in both RPMI and RPMI/L-15. These results suggest that the optimal culture conditions for blastogenic responses of mammary mononuclear cells and peripheral blood lymphocytes may differ.