Effect of injectable copper, selenium, zinc and manganese on the pregnancy rate of crossbred heifers (Bos indicus × Bos taurus) synchronized for timed embryo transfer

The success of synchronization protocols for timed embryo transfer (TET) depends on various factors such as breed, body condition scores and nutrition (including trace mineral status). In the present study, crossbred heifers were treated with subcutaneous injectable trace minerals (ITM - 100 mg zinc, 100 mg manganese, 50 mg copper and 25 mg selenium; Multimin®, Minerthal, Brazil) 17 days prior to embryo transfer. Estrus synchronization for TET, conception rate and pregnancy loss were evaluated. Subcutaneous administration of ITM did not increase the number of heifers successfully synchronized compared to non-injected controls [ITM group = 82.1% (308/375) versus control = 83.1% (375/451); P = 0.76]. However, heifers belonging to the ITM group (n = 219) had a 1.58 fold and 1.72-fold higher (P = 0.005) odds of being pregnant 23 and 48 days after TET compared to the control group (n = 276; not receiving ITM), respectively. In contrast, treatment with subcutaneous ITM did not significantly lower the pregnancy-loss rate [control group = 17.2% (17/99) versus ITM group = 10.6% (11/105); P = 0.18]. Even though subcutaneous administration of ITM 17 days prior to TET did not increase the number of heifers successfully synchronized, a significant increase in the conception rate (embryo survival) at 23 and 48 days after TET was noted in heifers of the ITM group.