Absorption and Retention of Trace Minerals in Adult Horses

Professional Animal Scientist, Jun 2005 by Wagner, E L, Potter, G D, Eller, E M, Gibbs, P G, Hood, D M

Abstract

Absorption and retention of Cu, Mn, and Zn were compared when feeding diets supplemented with oxide, sulfate, or organic-chelated forms of the minerals. Six mature Miniature Horses were used in the replicated 3 � 3 Latin square-designed experiment. The experiment was conducted in three 17-d periods, consisting of 10 d of diet adaptation followed by a 7-d total fecal and urine collection. Horses were fed a diet of 40% coastal Bermudagrass and 60% concentrate formulated to meet the energy, protein, Ca, and P requirements for maintenance of mature horses. Copper, Mn, and Zn were supplemented to provide 140 to 180% of the NRC (1989) recommended dietary concentrations for these minerals and were supplied in oxide, sulfate, and organic-chelate forms. Following total collections offeces and urine, feed, fecal, and urine samples were processed and analyzed for Cu, Mn, and Zn concentrations by atomic absorption spectrophotometry. Absorption of Cu, Mn, and Zn in all forms was low compared with previous studies, but systemic retention of these minerals was high. The cause of this disparity is unknown, although experimental error is unlikely. There were no differences in the absorption or retention of Cu, Mn, and Zn among the three forms of mineral supplements. Mature, idle horses may not be appropriate animals in which to evaluate absorption of various forms of trace minerals.

(Key Words: Trace Minerals, Absorption, Oxide, Sulfate, Organic-Chelate.)

Introduction

Copper, Mn, and Zn are important nutrients in the diets of horses, with integral roles in such processes as bone matrix formation and hoof strength (Jackson, 1998). These minerals can be supplemented in the diet as inorganic oxides, sulfates, or organic chelates with the mineral bound to an amino acid or peptide complex. Differences in the absorption and incorporation of these mineral supplement forms have been noted in several livestock species (Baker and Ammerman, 1995a,b; Henry, 1995). Ashmead et al. (1985) suggested the differences in absorption are due to the specific ion-friendly conditions required by inorganic minerals compared with the less energy-demanding uptake of chelated minerals bound to and absorbed with their low molecular weight, amino acid complex. The latter transport method is hypothesized to result in an increased rate of absorption and incorporation of minerals into body tissues.

Differences in absorption, retention, and bioavailability among oxide, sulfate, and organic-chelate mineral supplements for non-equine species have been reported (Henry et al., 1986, 1989; Spears, 1989; Baker et al., 1991; Kegley and Spears, 1994; Sandoval et al., 1997), whereas other research has not been as conclusive (Apgar et al., 1995; Apgar and Kornegay, 1996). Research in horses on the various forms of trace minerals has been limited. When comparing an inorganic trace mineral supplement to an inorganic-organic blend, there was no difference in liver mineral concentration (Siciliano et al., 2001a) or hoof wall characteristics (Siciliano et al., 2001b) in mature horses. In another study, yearlings supplemented with a proteinate trace mineral mix had greater hoof growth rates than those fed an inorganic supplement, but there was no difference in hoof wall strength or skeletal growth characteristics between groups (Ott and Johnson, 2001). These studies have illustrated a need for a direct comparison of the absorption and retention of oxide, sulfate, and organic-chelate trace mineral supplements in horses. Furthermore, there is a tendency in the equine industry to feed these minerals at amounts greater than NRC (1989) recommendations, yet there have been few studies examining the efficiency of absorption at or near these values.

Materials and Methods

Six mature Miniature Horse geldings with an average BW of 90 kg were used in a replicated 3 � 3 Latin square-designed experiment. The experiment was conducted in three 17-d periods, divided into a 10-d diet adaptation period followed by a 7-d total collection. The diet treatments consisted of a control diet (40% hay:60% concentrate) balanced to contain sufficient energy, protein, Ca, and F for maintenance of mature horses. In each of the three experimental diets, Cu, Mn, and Zn were supplemented to provide 130 to 160% of the NRC (1989) recommended dietary concentrations for the minerals (Tables 1, 2, and 3). In one diet, supplementation was supplied by the oxide form, the second by the sulfate form, and the third by minerals in the organic-chelated form, provided as mineral-proteinate. All of the trace mineral supplements were provided by a commercial supplier. Concentrate was hand-mixed weekly and offered to the horses as a textured feed.

Horses were maintained on drylots between feedings. At feeding, horses were brought to individual concrete-floored stalls and offered feed from non-metal containers. Drylots were cleaned daily to remove waste and reduce the risk of coprophagy. The protocol for animal treatment was reviewed and approved by the Texas A&M University Agricultural Animal Care and Use Committee. Horses were placed in the drylot and fed to project standards for a minimum of 30 d prior to the beginning of the research period. During this time, horses were offered the basal diet.