Effect of Repeated Trace Mineral Injections on Beef Heifer Development and Reproductive Performance

To determine the effects of repeated trace mineral injections on heifer development and reproductive performance, commercial Angus heifers (n=290; 199±34.3 kg) were utilized in a completely randomized design. Heifers were stratified by BW into 6 groups and assigned to injectable trace mineral (MM; Multimin90) or saline injection (CON) given post-weaning at 221, 319, and 401±22 d of age. Throughout development, heifers grazed endophyte-infected fescue-red clover pastures and were supplemented with modified corn distillers grains (2.7 kg·heifer^-1·d^-1) and given access to free choice inorganic minerals formulated to meet or exceed NRC recommendations. Heifer BW and BCS were collected at trial initiation and 4-7 week intervals thereafter. Hair coat scores (HCS) and respiration rates (n = 30 heifers/treatment) were collected at 269, 310, and 361±22 d of age. Additionally, blood and liver samples were collected at trial initiation and estrous synchronization from 30 heifers/treatment to determine trace mineral status. At 319, 372, and 421±22 d of age, antral follicle count and ovarian size were determined via ultrasonography. Two blood samples from all heifers were collected 10 d apart, concurrent with ultrasound dates, for puberty determination. Estrous synchronization was initiated and reproductive tract scores (RTS) were collected at 421±22 d of age. Heifers had AI at 430±22 d of age. Heifer BW, BCS, and HCS did not differ (P ≥ 0.12) throughout development, except at 268±22 d of age when BCS was greater (P = 0.03) for MM than CON. Respiratory rates were greater (P = 0.05) for MM than CON at 269±22 d of age, but did not differ (P ≥ 0.66) at 310 and 361±22 d of age. Plasma Mn and Zn concentrations did not differ between treatments (P ≥ 0.54). However, MM had greater (P ≤ 0.01) plasma and liver concentrations of Cu and Se compared to CON. Interestingly, MM decreased (P = 0.02) liver Zn concentrations compared to CON and there was no difference (P = 0.60) in liver Mn concentrations. Antral follicle count and ovarian size did not differ (P ≥ 0.43) between treatments. Throughout development, the number of pubertal heifers was less (P < 0.01) for MM than CON. However, there was no difference (P ≥ 0.26) in RTS or AI pregnancy rates (36 and 37% for MM and CON, respectively). Supplementing an injectable trace mineral increased heifer Cu and Se status; however, no effect was noted on ovarian development or reproductive performance.