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; 221 +/- 22 d of age) were utilized in a completely randomized design. Heifers were stratified by body weight (BW) and were administered an injectable trace mineral (MM; Multimin 90) or saline (CON) given subcutaneously, post-weaning at 221, 319, 401, and 521 +/- 22 d of age. Throughout development, heifers grazed endophyte-infected fescue, red clover pastures and were supplemented with corn distillers grains (2.7 kg per heifer per day) and given access to free choice inorganic minerals. Heifer BW and body condition scores (BCS) were collected at trial initiation and 4- to 7-wk intervals thereafter. Hair coat scores (HCS) and respiration rates (n = 30 heifers per treatment) were collected at 269, 310, and 361 +/- 22 d of age. Blood and liver samples were collected at trial initiation and estrous synchronization from 30 heifers per 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 cyclicity determination. Estrous synchronization was initiated, and reproductive tract scores (RTS) were collected at 421 +/- 22 d of age, and heifers were bred via artificial insemination (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 heifers. Respiratory rates were greater (P = 0.05) for MM than CON heifers 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 (P >= 0.54). However, MM heifers 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. Antral follicle count and ovarian size did not differ (P >= 0.51) due to treatment. Throughout development, number of heifers cycling was lesser (P < 0.01) for MM than CON heifers. However, there was no difference (P = 0.19) in RTS, AI pregnancy rates, or overall pregnancy rates. Supplementing an injectable trace mineral increased heifer Cu and Se status; however, no effect was noted on ovarian development or pregnancy rates.