Abstract
Simple SummaryAdverse weather conditions and harvesting technique have broad effects on forage quality including contamination with soil particles, e.g., clay minerals. Clay minerals are organised in a layered structure which enables adsorption of bivalent cations. Accordingly, ingested clay minerals may interact with dietary bivalent trace elements, such as Cu, Fe, Mn, and Zn. This study aimed to assess the relationship between clay mineral ingestion and the solubility of dietary trace elements along the digestive tract in vitro. In the presence of clay minerals, we found a reduction of solubilised Zn, Cu, and Mn under ruminal, abomasal, and duodenal conditions. However, clay minerals led to an increase in dissolved Fe under abomasal and duodenal conditions. Therefore, ingested clay minerals may be assumed to alter the solubility of essential dietary trace elements in the digestive tract of ruminants.Ruminants ingest large quantities of clay minerals along with inorganic soil constituents in roughages. The layered structure of clay minerals, however, may adsorb cations and may, thus, interfere with the ruminants’ supply of essential trace metals, such as Zn, Mn, Cu, and Fe. As quantitative knowledge about interactions between clay ingestion and essential trace metal metabolism are largely lacking, this in vitro study focussed on the effect of clay on the solubility of dietary Zn and other bivalent trace metals in the digestive tract of ruminants. Therefore, buffered rumen fluid was used for the simulation of ruminal conditions (RC), acidified rumen fluid (pH 2) was used for abomasal conditions (AC), and duodenal chyme was used for duodenal conditions (DC). These media were added with gradient levels of zinc and incubated at 39 °C for 24 h in the absence or presence of clay minerals. Soluble Zn, Cu, Mn, and Fe were derived by centrifugation (10,000× g) of incubated media, and the supernatants were analysed. Clay depressed the solubility of added Zn in ruminal (65.3% vs. 16.5%), abomasal (97.7% vs. 33.7%), and duodenal conditions (41.3% vs. 21.1%), the results of which were statistically significant (p < 0.001). Moreover, clay reduced dissolved Cu (µg/mL) (RC: 0.13 vs. 0.10; AC: 0.16 vs. 0.13; DC: 0.10 vs. 0.08) and Mn (µg/mL) (RC: 3.00 vs. 1.80; AC: 5.53 vs. 4.80; DC: 3.18 vs. 1.77) (p < 0.05 in all cases). The presence of clay minerals increased the concentrations of solubilised Fe (µg/mL) in abomasal (1.80 vs. 2.86, p < 0.05) and duodenal conditions (1.76 vs. 2.67; p < 0.05). In total, the present in vitro study demonstrates the potential of clay minerals ingested with ruminant feeds for depressing the solubility of dietary Zn, as well as the depression of dietary Cu and Mn along the passage of the digesta from the rumen until the duodenum. Additionally, clay minerals may release Fe into the digesta.
Highlights
IntroductionThe crude ash content of forages is an indicator of undesired contamination with inorganic soil components and should not exceed 10% of dry matter (DM) [1]
Buffered rumen fluid was used for the simulation of ruminal conditions (RC), acidified rumen fluid was used for abomasal conditions (AC), and duodenal chyme was used for duodenal conditions (DC)
After digestion with nitric acid, the clay mineral mixture was analysed for its mineral content (Table 2) using inductively coupled plasma mass spectrometry (ICP-MS; PerkinElmer, Waltham, MA, USA)
Summary
The crude ash content of forages is an indicator of undesired contamination with inorganic soil components and should not exceed 10% of dry matter (DM) [1]. Most of the inorganic fraction of soil constitutes silicates in conjunction with cations [8]. One main category of silicates is represented by clay minerals. Clay minerals are organised into a layered structure of silica and alumina sheets, which has a surface with negative charges that may adsorb cations, such as protons and metal ions [9,10]. Cation sorption sites occur, where the resulting layered structure of octahedral and tetrahedral sheets becomes negatively charged [11]. The pattern of clay minerals present in the soil substantially influences the overall adsorptive potential, with the type of clay minerals and the density of the layer structures within the clay mineral being the most prominent determinants
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