Effect of complexed trace minerals on cumulus-oocyte complex recovery and in vitro embryo production in beef cattle1,2.

The objective of this experiment was to evaluate the impact of complexed trace mineral supplementation on ovum pick-up (OPU) and in vitro embryo production in lactating beef cows. Thirty days prior to fixed-time artificial insemination (FTAI; day -30), 68 postpartum cows were stratified by BW, BCS, and parity before being randomly assigned to 10 pens of either a treatment (TRT; n = 5) or a control (CNT; n = 5) group. Each group received a weekly mineral supplement allotment of 1.16 kg × week-1 × cow-calf pair-1 for 14 wk. Cows assigned to the TRT group received a mineral supplement that contained amino acid complexes of zinc, copper, and manganese, as well as cobalt glucoheptonate (Availa Plus; Zinpro Corp., Eden Prairie, MN, USA), while cows assigned to the CNT group received a mineral supplement that was formulated to contain similar concentrations of these trace minerals from inorganic sources. All cows were submitted to a 7 d CO-Synch + CIDR protocol on day -10 and bred using FTAI on day 0. Pregnancy diagnosis was performed on day 28 and nonpregnant cows were removed. All pregnant cows were subjected to ovum pick-up (OPU) on day 52 and 67 of gestation. Cumulus-oocyte complexes (COCs) were evaluated and graded prior to in vitro fertilization (IVF). Analysis of variance was conducted to determine effects of treatment on response variables, and pen was considered the experimental unit. Supplement consumption did not differ (P = 0.48) between treatments (1.16 ± 0.12 vs. 1.07 ± 0.15 kg of DM × week-1 × cow-calf pair-1 for TRT and CNT, respectively). Total COC recovery was greater (P = 0.03) from TRT when compared with CNT cows (22.4 ± 2.0 vs. 16.4 ± 1.4 COCs × pen-1, respectively) and the number of COCs meeting maturation criteria was increased in TRT cows (P = 0.05) when compared with CNT cows (15.9 ± 1.6 vs. 11.8 ± 1.0 COCs × pen-1, respectively). Production of transferable embryos tended to be greater (P = 0.06) for TRT than CNT cows (4.7 ± 0.6 vs. 2.7 ± 0.7 embryos × pen-1, respectively). Furthermore, when expressed as a ratio, the number of recovered COCs meeting maturation criteria that were required to produce a transferable embryo tended to be lower for TRT than CNT cows (3.10 ± 0.93 vs. 7.02 ± 1.60; P = 0.06). In summary, complete replacement with complexed trace mineral improved COC recovery and in vitro embryo production when compared with inorganic forms of these trace minerals in beef cows.