Effects of Mineral Supplementation During Range Grazing on Ovine Performance

Abstract Western US sheep production systems are dependent on rangeland forages to meet nutritional needs for animal production. While many native rangeland soils and forages are deficient in minerals like Cu, Se, and Zn, it is unknown whether ewes will alter forage selection if they receive a mineral supplemented diet and if alternative forages will affect performance on range. The objectives of this study are to quantify the effects of mineral supplementation on ewe forage selectivity on rangeland, range utilization, and animal performance. We hypothesized ewes who receive a trace mineral supplement will have a more diverse diet, greater rangeland utilization, and improved performance characteristics than their non-supplemented contemporaries. In this study, (n = 59) ewes were grazed across four summer pastures on Cedar Mountain near Cedar City, Utah. Ewes between the ages of 1 and 6 with an average weight of 87 Kg ± 13 Kg were stratified by initial weight and breed into one of two different treatment groups: 1) trace mineral supplement ad libitum (TRT; n = 30), or 2) no mineral supplement (CON; n = 29). Ewe breed types consisted of black face type breeds (BLF; Suffolk) and white face type breeds (WF; Targhee, Rambouillet, and their crosses). All ewes received a similar diet of alfalfa hay and triticale without access to ad libitum mineral supplementation 30 days before the start of the trial. A solar powered C-lock inc. pro was used to track individual animal mineral intake. Back fat (BF) and loin eye depth (LED) were measured at day 0 and day 116 of the trial via ultrasound. Additionally, fecal samples were collected and used for fecal metabarcoding (fDNA) at approximately 30% pasture utilization, which measures the proportion of plant DNA in the feces to determine forage species consumed. Plant species were sorted into functional groups (forbs, grass likes, grasses, shrubs, and trees). The GLM procedure of SAS was used to analyze BF, LED, and fDNA. The mixed procedure of SAS with day as a repeated measure was used to analyze percentage change in body weight. Control ewes had greater BF by 0.08 cm (P = 0.02). No difference in BF was observed by breed (P = 0.8). Loin eye depth was greater by 0.2 cm (P = 0.01) in BLF ewes than WF ewes. Supplemented ewes maintained 1% more of their initial body weight than CON ewes (P = 0.01). No forage selection differences were observed by treatment or breed (P> 0.2). The current study results indicate that mineral supplementation on range may not affect forage selectivity but can benefit animals by maintaining body weight over the grazing season.