Influence of soil contamination before and after ensiling on mineral composition of grass silages, feed intake and carry-over to body tissue of goats

Iron (Fe) is ubiquitous in the environment and has possible impact on quality and safety of feed and food due to the fact that it can be transferred from soil to animal feed and further to the products of animal origin. Therefore, the objective of the present study was to evaluate the effect of contamination of forage with soil differing in Fe concentration on Fe solubility, mineral composition and quality of grass silages. Furthermore, the effect of feeding these silages on feed intake, performance, trace element absorbability and carry-over into edible tissues was tested in young goats. Two ensiling experiments revealed that treating grass without or with different levels and types of soil before ensiling did not affect fermentation parameters of silages. Nevertheless, the addition of soil caused a highly significant increase of crude ash and trace elements contents in forage and silages. During ensiling, the in vitro solubility of Fe increased on average 5 times. Also, the aluminium content was the best indicator of soil contamination in forages. In a feeding trial with growing goats, feed intake and live weight gain were decreased in the group fed grass ensiled with the soil in contrast to the control group and animals receiving feed with soil added just before feeding. Fe concentration was highest in the duodenal tissue of kids fed the forage contaminated with soil before ensiling (184 vs 88-80 mg Fe/kg DM in the other two treatments), which might be also an indicator of Fe regulating properties. Fe concentration in the liver increased likewise. In conclusion, data indicate that ingesting ensiled soil impairs animal performance.