Dietary Trace Mineral Level and Source Affect Fecal Bacterial Mineral Incorporation and Mineral Leaching Potential of Equine Feces

Abstract

Minerals excreted in feces have the potential to leach or runoff to water-ways, negatively impacting water quality. This study examined the effect of dietary trace mineral levels, and their source, on the leaching potential of minerals from equine feces. Nine horses were used in a replicated 3 × 3 Latin Square, with three dietary treatments provided as pellets: no added trace minerals (CON), added inorganic trace minerals (ING), and added organic trace minerals (ORG). Supplemental trace minerals included Co, Cu, Mn, and Zn. Horses were allowed ad libitum access to forage and fed their treatment pellets for 16 days prior to fecal sample collection. Estimated dietary mineral intake exceeded requirements for supplemented minerals. Regardless of the source, adding dietary trace minerals increased the fecal leaching potential of Cu, Zn, and P (p < 0.05). More Co leached from ORG compared to ING, while Zn leached in greater amounts from ING compared to ORG (p < 0.05). Fecal bacterial Zn content was greater (p < 0.05) for ORG compared to ING. Negative correlations were observed between bacterial mineral content and leaching for several minerals. Supplementing trace minerals in forms that increase microbial incorporation may provide a strategy to control fecal mineral leaching.Sustainability 2019, 11, 7107 2 of 12 commonly available organic trace minerals used in domestic animal diets include Co, Cu, Mn, Fe, and Zn [13]. The value of replacing inorganic trace minerals with organic sources can include the increased bioavailability of the mineral to the animal, and also increased availability for uptake by intestinal microorganisms. An increase in the bioavailability of the mineral might result in less mineral being excreted, depending on the biological need for that mineral by the horse. Increased uptake by microbes is believed to reduce the solubility of the mineral and could thus have an impact on the leaching potential of that mineral, as shown in soil microbial communities and P leaching potential [14,15]. However, the effect of the trace mineral source on the leaching potential of equine manure has not been investigated.The objective of this study was to examine the effect of trace mineral level and source (inorganic or organic) on fecal mineral excretion, bacterial mineral incorporation, and fecal mineral leaching potential. The hypothesis was that the supplementation of trace minerals to well above recommended amounts [12] would increase the fecal excretion of those minerals and that organic trace minerals would reduce leaching potential. Materials and MethodsThe animal part of this study was approved the Institutional Animal Care and Use Committee at the University of Kentucky.Nine mature geldings (mean ± SD; 9.1 ± 2.1 years; 600.9 ± 50.6 kg initial body weight (BW)) were blocked by age into three groups. The groups were housed in pastures containing cool-season grasses and clovers. When the pasture supply was not sufficient due to changes in season, grass hay that was cut from the same farm was supplied in the fo...

Trace Mineral Leaching from Equine Compost

“…Additionally, DM disappearance was not different among treatments, so Zn should be equally concentrated in the compost treatments due to similar DM losses. Due to the decrease in organic matter content, concentrations of all minerals were greater in the compost compared to the pre-composted feces, which were reported in another study [18]. Briefly, feces from horses supplemented with trace minerals (ING and ORG) had significantly greater concentrations of Cu and Zn, and tended to have greater concentrations of Co compared to CON [18].…”

“…Due to the decrease in organic matter content, concentrations of all minerals were greater in the compost compared to the pre-composted feces, which were reported in another study [18]. Briefly, feces from horses supplemented with trace minerals (ING and ORG) had significantly greater concentrations of Cu and Zn, and tended to have greater concentrations of Co compared to CON [18]. Other studies have also reported an increase in mineral concentration after composting [6].…”

“…The reason why Zn concentration was greater in ING compost is unknown. The concentration of Zn was similar in the feces used to generate the ING and ORG composts [18]. Leaching losses were not possible in our compost system, so there would be no route for Zn to leach from any of the composts.…”

“…Approximately 1.75 kg of wet feces was saved and stored at −20 • C for mineral analysis and leaching. Those data are reported in a companion paper [18]. The remaining fecal material for each horse was composted.…”

“…Compost samples were leached using an apparatus that simulates a rainfall event and allows for capture of the leachate. This method has been described elsewhere [18]. After leaching, the leached compost samples were dried at 55 • C for 24 h and ground for analysis.…”