Pharmacologic and toxicologic properties of humic acids and their activity profile for veterinary medicine therapy

Humic acids derive from a class of natural substances in humic substances. The chemical properties of certain defined humic acid products enable their application in diseases of the digestive system of mammals when combined with metabolic disorders, especially in rearing age. The simple administration (via feed), their exceptional safety and the absence of side effects (e. g. allergy, resistance) as well as no residue formation in animal derived products allow a broad application of these substances in veterinary medicine, even when regarding ecotoxicological aspects.     

Resistance to triforine: A nonexistent problem?

Permanent resistance to triforine in Cladosporium cucumerinum was obtained after UV irradiation of spore suspensions and selection of resistant strains in the presence of triarimol or triforine. About 50 strains were examined for mycelial growth on malt agar, viability upon routine subculturing, growth and inhibition by triforine in thin-layer chromatographic bioassays, and virulence towards cucumber seedlings. In addition, sporulation and spore germination, as well as effects of ergosterol were investigated in a restricted number of strains. Although all strains differed considerably from each other in these characteristics, they were quite similar in a reduced overall-fitness. These triforine-resistant mutants of C. cucumerinum might, therefore, have a greatly reduced chance of survival in competition with the wild-type strain, as was actually demonstrated for two strains in greenhouse experiments with mixed-inoculations of cucumber seedlings. Such a reduced chance of survival might also explain why under practical conditions development of resistance to triforine has not been observed yet.The triforine-resistant C. cucumerinum strains showed cross-resistance to a number of systemic fungicides known or supposed to inhibit ergosterol biosynthesis, viz. Denmert, fenarimol, imazalil, triadimefon and triarimol. The practical implications and potential hazards of such cross-resistance for the use of already established fungicides are discussed.     

The digestibility of crude nutrients in horses. 1. Methods of determining digestibility

The ascertainment of the digestibility of crude nutrients in rations for horses requires the inclusion of movement-based performance as influencing factor. Under the consideration of this requirement, indicator methods gain significance in comparison with the standard method of collecting faeces completely. In two experiments the digestion of the crude nutrients in rations for horses was tested according to the standard method (complete collection of faeces) and the indicator method 4 N HCl-insoluble ash). According to the indicator method the digestibility of crude nutrients was slightly higher, the differences to the values of the standard method were statistically insignificant. Under consideration of the inhomogeneity of horse faeces and the possibility of doing without the complete collection of faeces, the indicator method with 4 N HCl-insoluble ash is to be preferred to the standard method. The analysis of air-dried faeces connected with the indicator method resulted in improved reproducibility due to the significantly better homogeneity. A recommendation is made for carrying out digestibility experiments with horses, in which the 4 N HCl indicator method is used.     

Comparison of the sensitivity of in vitro and in vivo tests for detection of the presence of a bovine viral diarrhoea virus type 1 strain

Veterinary vaccines are usually tested for the absence of contaminants. However, the quality control does not always imply that vaccines are not contaminated as, for example, illustrated by the bovine herpes virus 1 (BHV1) vaccine used in The Netherlands in 1999 that contained a small amount of bovine viral diarrhoea virus (BVDV1). Thousands of cows were vaccinated with BHV1 vaccine batches, and the question arose as to whether these small amounts of BVDV1, most likely not detected with in vitro tests, could have infected cattle. More in general, the question was whether the outcome of the in vitro tests, i.e. the in vitro infectivity, was indicative for the infectivity for cattle, i.e. the in vivo infectivity. We therefore carried out in vitro experiments to determine the sensitivity of a BVDV1 isolation assay. In addition, we performed two animal experiments, in which we estimated the lowest dose needed to infect calves with BVDV1. We extrapolated the experimental in vitro and in vivo results from a tissue culture infectious dose (TCID50) to a cattle infectious dose (CID50). We observed a partial response in the calves inoculated with this dose: four out of six calves turned out to be infected. In the tissue culture test, all 20 samples tested negative. The response in vivo, however, was not significantly higher than the in vitro response, which implies that no difference in susceptibility was observed between the animal test and the tissue culture test. Based on the results in our experiments, some cattle may have been infected with BVDV1 after the application of the contaminated BHV1 vaccine during the vaccination campaign. The question remains that how many cattle received contaminated vaccine, and became infected with BVDV1.