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Red Angusbased, Mayborn heifers (n = 799) at 2 locations were utilized to determine the effects of an injectable trace mineral on reproductive performance. Heifers were managed at the Maddux ranch near Wauneta, NE. Following weaning in October, heifers were backgrounded in a feedlot (Table 1) until a body weight (BW) of 650 lb was reached and then moved to graze native range at location 1 (L1, n = 125) or location 2 beginning in early March (L2, n = 286). A subset of heifers (n = 388) grazed corn residue with cows over winter, weaned in April, and backgrounded in a feedlot until target BW of 650 lb was attained and then transported to L1 and L2 finishing in early June. Heifers were offered free-choice mineral at both locations. Initial mineral status was analyzed via liver biopsy prior to mineral treatment (677 lb, n = 22). Initial liver concentrations of copper (146 μg/g), manganese (9.22 μg/g), selenium (1.54 μg/g), and zinc (115 μg/g) were adequate and not different (P > 0.26) among heifers managed at the 2 overwinter locations (Table 2). Heifers were synchronized with a 14d controlled internal drug release (CIDR)prostaglandin F2α protocol (Figure 1) and either injected with a trace mineral (5 ml, MULTIMIN, n = 399) or received no injection (CON, n = 400) the day of CIDR insertion. Fertile bulls were placed with heifers on range for 60 d following AI (1:17 tation free-choice; however, tracemineral intake can vary. Furthermore, dietary tracemineral absorption may be reduced due to negative interactions with other nutrients during digestion. An injectable tracemineral (ITM) solution used with free-choice trace minerals may be beneficial before breeding to increase mineral status. Heifers given an ITM in conjunction with a freechoice mineral supplement have shown an increase in conception rates to timed embryo transfer. Additionally, conception to fixedtime AI was greater in ITM cows when compared with salinetreated cows. Conversely, a more recent study noted no differences in reproductive performance of feedlotdeveloped heifers given an ITM 30 d prior to the breeding season when adequate concentrations of trace mineral were provided in the diet. Limited research has been conducted concerning the effects of an injectable trace mineral administered at CIDR insertion on reproductive performance of extensivelydeveloped beef heifers. Heifers developed extensively represent those managed under dormant or scarce forage conditions, low precipitation, undulating terrain, or restrictedgain pen developed. Therefore, the objective of the current study was to determine if an injectable trace mineral at CIDR insertion affected reproductive performance of rangedeveloped beef heifers. Shelby A. Springman John G. Maddux Mary E. Drewnoski Rick N. Funston

321 Effect of injectable trace mineral on reproductive performance in beef heifers