PSIX-26 - Effectiveness of mineral supplementation during range grazing on mineral status in ewes

Abstract: Mineral supplementation in the intermountain west region of the US may be necessary for maintenance of healthy flocks since important trace minerals are deficient in this region. However, rough terrain can make mineral supplementation challenging. The objective of this study was to evaluate the trace mineral status of ewes on range. We hypothesized that ewes with access to a mineral supplement would have decreased risk of mineral deficiency. In this study, ewes (N = 59) grazed four summer pastures on Cedar Mountain near Cedar City, Utah. Ewes between the ages of one and six years old were stratified by initial weight (87 kg ± 13 kg) and breed [black face (BLF; Suffolk) and white face breeds (WF; Targhee, Rambouillet, and their crosses)] into two treatment groups: 1.) trace mineral supplement ad libitum (TRT; n = 7 BLF and 23 WF) or 2.) no mineral supplement (CON; n = 15 BLF and 14 WF). All ewes received a diet of mixed alfalfa and triticale hay without mineral supplementation 30 d before the trial began. A SmartFeed™ (C-lock Inc.) was used to track individual animal mineral intake. Plasma samples were collected via jugular venipuncture at d 0, 34, 77, and 116. A clinical veterinarian from Utah State University performed liver biopsies at d 0 and 116 on a subset of ewes (n=10). After the grazing season, plasma and liver samples were sent to the Iowa State University VDL for analysis of Cu, Mn, Se, and Zn. The mixed procedure of SAS was used to analyze plasma mineral content with day as a repeated measure and individual ID as a random variable. The Glimmix procedure of SAS was used to analyze liver mineral content. Plasma Cu and Se increased (P≤0.05) by day in all ewes throughout the grazing season. No differences related to treatment or breed (P >0.10) were observed for plasma Cu or Se levels. Plasma Mn and Zn decreased (P < 0.0001) by 1.5 ppb and 0.4 ppm, respectively, between d 0 and 116 with no treatment effect (P >0.10). BLF ewes had 0.3 ppm (P=0.01) greater plasma Mn concentrations than WF ewes, with no difference (P=0.6) observed due to treatment. Hepatic Cu and Se increased (P≤0.05) by 114 ppm and 1 ppm, respectively, between d 0 and 116. Hepatic Mn concentrations did not differ (P >0.10) by day or treatment. Hepatic Zn concentrations tended to increase by day (P=0.07), 23 ppm between d 0 and 116. CON ewes had 28 ppm greater (P=0.04) hepatic Zn concentrations than TRT ewes. Additional research is warranted to understand why CON had greater hepatic Zn levels than TRT, which may indicate that diverse rangeland forages may provide sufficient concentrations for sheep production in summer months.