005 Evaluation of Metal Loss through Simulated Rainfall-Induced Leaching of Salt-Based, Free-Choice Mineral Supplements: An Extension Service

Abstract

Previous research identified preferential intake of Cu, Zn, and Mn-fortified supplements containing Zn and Mn hydroxychloride and basic Cu chloride vs. sulfate and organic forms of these metals among young beef calves. However, in the days following significant rainfall events, the preferential differences lessened. In addition, visual observation of the colored pooled water collecting under the raised mineral feeders suggested rainfall-induced leaching of trace minerals. Therefore, we designed a series of experiments to investigate rainfall-induced metal losses under laboratory conditions. From these efforts, a simplified laboratory procedure was established allowing benchtop evaluation of rainfall-induced leaching susceptibility from free-choice, salt-based mineral supplements. This procedure is now available as an extension service of the UF-IFAS, Range Cattle Research and Education Center. Briefly, the procedure is designed to simulate a 10.2 cm rainfall occurring over 3 separate events (3.4 cm on Monday, Wednesday, and Friday). The procedure requires a minimum of 4 kg of mineral supplement being tested, which is divided into 4, 1 kg subsamples. A single pre-leaching sample (250 g) is collected from each of the subsamples and the remaining 750 g of sample is placed into Buchner funnels (177 cm2) on 20 to 25 µ pore filter paper. Deionized water (pH adjusted to 5.6) is poured over the mineral and the leachate collected into volumetric flasks. Along with the original pre-leaching sample, the remaining leached mineral is dried, weighed and analyzed for Cu, Zn, and Mn concentration using inductively coupled plasma spectroscopy techniques. Metal loss is estimated by calculating the difference between the total metal in the initial pre-leached sample less the metal remaining in the leached sample. Results are presented as percent metal loss ± SD of the 4 replications. The service is offered for $350 per sample with a turnaround time of approximately 14 d. In addition to leaching loss of trace metals, the analysis also provides important comparison between labeled nutrient specifications and actual chemical analysis. Results provide both manufacturers and producers with an understanding of the potential for essential nutrient losses due to rainfall interactions with free-choice, salt-based mineral and assist in evaluating the economic advantages of increased frequency of supplementation, use of weathering agents, and investment in rainfall-protected mineral feeders.