[Animal-derived feedstuffs as possible vectors for bovine encephalopathy (BSE) in Germany. Part 2: Assessment of vector risk for compounded feed]. / Futtermittel tierischer Herkunft als mögliche Verbreitungsursache für die bovine spongiforme Enzephalopathie (BSE) in Deutschland. 2. Mitteilung: Einschätzung des Verbreitungsrisikos über Mischfutter.

Specific conditions and practices of cattle feeding in Germany have to be taken into account for assessing the risk of feed born transmission of bovine spongiform encephalopathy, especially regarding the situation before the year 2000 when specific directives were introduced for feed production. The present retrospective epidemiological study includes data on feed production and the estimated amount of animal derived feedstuffs for the production of compounded feed for cattle. Risk assessment was performed based on the 'reproduction rate' (R0), that is defined as the estimated number of infections resulting from the processing of brain and spinal cord of BSE affected cattle that is recycled to bovines via feed. Under the conditions as given in Germany until the year 2000 the reproduction rate of BSE via the inclusion of animal derived feedstuffs in compounded feed production for cattle was estimated to be 1.1. Thus, it can be expected that BSE could be reproduced in the system, but with comparatively low efficiency. The expected incidence of BSE should be considerably lower compared to the situation during the 90th in the UK, due to the markedly lower recycling rate of animal protein in cattle feeding. Animal fat could have been a significant factor for BSE transmission due to contamination by proteinaceous brain and spinal cord material during the production process. The relative significance of fat containing feedstuffs for BSE transmission could have been higher in Germany compared to the situation in the UK where meat and bone meal was produced under different conditions and frequently used in higher proportions as an ingredient for compounded feed for ruminants.

[Animal-derived feeds as possible vectors for bovine spongiform encephalopathy (BSE) in Germany. 1. Comparative risk assessment for a single animal food of animal origin]. / Futtermittel tierischer Herkunft als mögliche Verbreitungsursache für die bovine spongiforme Enzephalopathie (BSE) in Deutschland: 1. Mitteilung: Vergleichende Risikobewertung der Einzelfuttermittel tierischer Herkunft.

The occurrence of BSE cases in Germany after the ban of meat and bone meal for ruminant feed in 1994 requires a detailed investigation of animal derived feedstuffs regarding their specific risks as vectors for the disease. Accepting the theory that BSE is a prion transmitted disease, the theoretical infectious potential was calculated for animal derived feedstuffs. This calculation was based on the assumption, that risk material (brain, spinal cord) of one clinically diseased cattle was rendered in the process as established in Germany (133 degrees C, 3 bar, 20 min) or, alternatively, that one diseased animal was slaughtered resulting in normal processing of the by-products for human food production. From this risk assessment it became obvious that meat and bone meal was one, but probably not the most important source for the spreading of BSE. Taking into account the high sensitivity of calves it can be speculated that certain products, e.g. from bone processing (bone meal) and fat melting (mixed animal fats), commonly used for the formulation of milk replacers, might have been more important as pathways. As it can't be excluded retrospectively that infected meat and bone meal was imported from the UK, this non-calculable influence may have been related to the significance of the other products. The calculation model underlines that efficient removal of specified risk material (brain, spinal cord) and adequate processing (133 degrees C, 3 bar, 20 min) or alternatively other equivalent treatments of fats are prerequisites for minimising the risk of feed borne transmission of BSE by animal derived feedstuffs. The epidemiological consequences are part of a subsequent paper.

Partially carboxymethylated feather keratins. 2. Thermal and mechanical properties of films.

Free cysteine thiol groups of keratin extracted from chicken feathers were partially carboxymethylated with iodoacetic acid (25-76% cysteine modification). Stable dispersions were used for the preparation of films by solution casting. Glycerol was used as a plasticizer (0.05-0.47 g/g of keratin), and films were stored at a constant relative humidity (20, 30, 50, 70, or 90%). The degree of crystallinity in the films was higher when more cysteine residues were carboxymethylated. The films displayed an optimum in mechanical properties at approximately 50% cysteine carboxymethylation. The tensile strength at this optimum was 25 MPa, the E modulus, 350 MPa, and the elongation at break, 50%. Probably, this optimum was the result of both a decreasing amount of disulfide bonds and an increasing degree of crystallinity for higher degrees of cysteine modification. The influences of a higher amount of glycerol and of different storage conditions on the mechanical properties of films from keratin with a defined degree of cysteine modification were also investigated.

Partially carboxymethylated feather keratins. 1. Properties in aqueous systems.

Feather keratins were extracted from chicken feathers with an aqueous solution of urea and 2-mercaptoethanol. The keratin solution obtained was dialyzed to remove the reagents. Upon dialysis, extensive protein aggregation occurred. To obtain stable solutions or dispersions in water, cysteine residues were modified prior to dialysis with iodoacetamide, iodoacetic acid, or bromosuccinic acid, thereby blocking free thiol groups and introducing hydrophilic groups. For the development of biodegradable materials with good mechanical properties from these biopolymers, disulfide bonds between the keratin molecules are needed. Therefore, cysteine residues were only partially modified by using different reagent/cysteine molar ratios. The reaction rate constants of iodoacetate with glutathione and 2-mercaptoethanol were successfully used to predict the degree of modification of keratin cysteine. It was shown that, for carboxymethylated keratin, fewer aggregates were formed for higher degrees of cysteine modification, while more protein was present as oligomers. Aggregates and oligomers were stabilized through intermolecular disulfide bonds.

Studies on the efficacy of hyperbaric rendering procedures in inactivating bovine spongiform encephalopathy (BSE) and scrapie agents.

The efficacy of the procedures in use at the two rendering plants in the Netherlands was assessed on a laboratory-scale using procedures that simulated the pressure cooking part of the rendering process. A pool of bovine spongiform encephalopathy (BSE)-infected brainstem from the United Kingdom and a pool of scrapie-infected brainstem from Dutch sheep were used to spike the rendering materials. The mixtures were subjected to various time-temperature combinations of hyperbaric heat treatment related to the conditions used in Dutch rendering plants in the early 1990s, and to the combination of 20 minutes at 133 degrees C required by the EU Directive on rendering of 1996. The efficacy of the procedures in inactivating BSE or scrapie infectivity was measured by titrating the materials before and after heat treatment in inbred mice, by combined intracerebral and intraperitoneal inoculations at limiting dilutions. Two independent series of experiments were carried out. The design of the study allowed for minimum inactivations of up to 2.2 log (2.0 in the second series) to be measured in the diluted infective material and 3.1 log in the undiluted material. After 20 minutes at 133 degrees C there was a reduction of BSE infectivity of about 2.2 log in the first series (with some residual infectivity detected), and in the second series more than 2.0 log (with no residual infectivity detected). With undiluted brain material there was an inactivation of about 3.0 log (with some residual infectivity detected). With the same procedure, scrapie infectivity was reduced by more than 1.7 log in the first series and by more than 2.2 log in the second series. With undiluted brain material there was an inactivation of more than 3.1 log. In each case no residual scrapie infectivity was detected. The BSE agent consistently appeared to be more resistant to heat inactivation procedures than the scrapie agent, particularly at lower temperatures and shorter times.