Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/20/2000
Publication Date: 6/20/2000
Citation: GRINGS, E.E., POLAND, W.W. EFFECT OF HAY SOURCE AND LEVEL ON TISSUE TRACE MINERAL CONCENTRATIONS IN GROWING STEERS. WESTERN SECTION OF ANIMAL SCIENCE PROCEEDINGS. 2000. p. 490-493. Interpretive Summary: Understanding the use of minerals from forages is critical to developing cost effective supplementation strategies, however, information on mineral utilization from forages is lacking. Western wheatgrass is a major forage species on Northern Great Plains rangelands. Mineral profiles of western wheatgrass have been reported but little information is available on the availability of these minerals. This study was designed to evaluate the impact of increasing intake on tissue mineral concentrations of steers fed western wheatgrass or alfalfa hays. Steers were fed alfalfa or western wheatgrass hay at two levels of intake for about 91 days. Tissue samples were collected at slaughter and analyzed for mineral content. Ruminal mineral disappearance was determined using nylon bags incubated in the rumen of steers fed the four diets. Some organ trace mineral levels and concentrations were altered by feeding different forages. Some of these alterations were due simply to differing trace mineral concentrations in the forages while others were related to differing solubilities within the gastrointestinal tract. Additional work is needed to evaluate the interrelationship of altering organ mass through changing nutrient densities on mineral metabolism.
Technical Abstract: Twenty-four steers (avg 410 kg) were fed alfalfa or western wheatgrass hay at either 1.90 or 2.35% of BW for 91 d to evaluate the effects of hay type and feeding level on tissue trace mineral concentrations. At the end of the feeding period, steers were slaughtered at a commercial abattoir. Tissue weights and samples were collected; samples were oven dried and analyzed for Cu, Zn, Mn, and Fe by atomic absorption spectrophotometry. Data were analyzed with a model including hay source and intake level, their interactions, and BW as a covariate. Alfalfa hay contained 7 ppm Cu, 17 ppm Zn, 30 ppm Mn, 426 ppm Fe, and 3.6 ppm Mo. Grass hay contained 2 ppm Cu, 20 ppm Zn, 29 ppm Mn, 143 ppm Fe, and 1.3 ppm Mo. Increasing hay intake by 124% increased intake of minerals but had little effect on tissue mineral concentrations. Heart Cu concentrations were greater in steers on the high than low intake level. Kidney Zn concentrations were affected by the hay source by level interaction. Liver weights averaged 1,466 g DM for alfalfa-fed and 1,276 g DM for grass-fed steers. On a dry tissue basis, total liver Cu, Zn, and Mn were affected by hay source, being greater in alfalfa-fed than grass-fed steers. For Zn and Mn this was due to increased liver weight but for Cu it was related to both increased concentration and liver weight in alfalfa-fed steers. Heart Zn concentrations and total heart Zn were greater for grass-fed (80.3 ppm and 25.7 mg) than alfalfa-fed steers. Kidney, heart, and muscle Mn concentrations were greater for alfalfa-fed than grass-fed steers even though Mn intake were similar. Differences in tissue mineral concentrations among steers fed different hays are related to more than mineral intake.