The Brazilian tannery industry produces annually an enormous amount of scraps and leather shavings impregnated with chromium due to the tanning process. Technologies have been developed to remove chromium from this material. The resultant residue from the chromium removal process is high in protein with a high digestibility, suggesting that this residue may be used to feed monogastric animals. However, due to the nature of this residue, there is a risk of chromium poisoning and the introduction of botulism. The aim of this work was to establish the risks of adding tannery residues to animal feeds, using rats as an experimental model. Forty-eight Wistar rats were placed under eight treatments in a 2 by 4 factorial arrangement. The rats were fed over 60 days with a standard AIN-93 diet and the treatments consisted of replacing part of the diet with 0, 25, 37.5 or 50% of the chromium-tanned leather residue, in natura, known as ‘wet blue’, or the same percentages of this residue after chromium extraction. Industrial processing was able to remove 70–80% of the chromium from the residue. This high chromium level had a negative effect on the weight gain of the animals and caused lesions in the kidneys especially due to the chromium extraction material, suggesting that the removal process increases the biological activity of chromium, making it nefrotoxic. The gravity of this effect was directly proportional to the inclusion level. The results of this study indicate that until industrial processing is refined so that more of the chromium residue is removed, the use of the tannery residues in animal feeds is not safe.
-The objective of this study was to find an alternative to minimize environmental contamination by leather waste using it as ruminant feed. The wet blue leather wastes (WB) without chrome extraction were compared with the leather wastes in which the chrome was extracted (CE). Both materials had 99.7% of dry matter (DM), but the crude protein level was higher (90.4%) in CE than in WB (74.3%). In situ effective ruminal degradability of DM was 59.7% and it was 63.1% for CP in CE. The WB did not suffer degradation in the rumen. In vitro abomasal digestibility of CE was 100%. The percentage of degradation per hour was higher for CE (8.2%) than for WB (0.08%). The mineral content was higher in wet blue leather wastes (10.4%) than in CE (0.4%) reflecting the chrome level and demonstrating that the removal process of this mineral is efficient. The use in animal feed is presented as a viable alternative for the disposal of waste and scrap generated by the leather tanning industry and treated by the extraction method, thus minimizing environmental contamination and providing a source of protein for animal feed.
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