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Mineral Sources May Impact Reproductive Efficiency

By Jonathan Sumption
 
Advancements in reproductive technologies have improved production efficiency of beef cattle in the world and continue to do so at a rapidly increasing rate. Many producers are familiar with embryo transfer. Another form of embryo collection is called in-vitro fertilization or ovum pick up (OPU) which harvests unfertilized oocytes directly from the ovaries of a donor cow or heifer. The oocytes are fertilized in a lab the day after collection and then they are grown in an incubator that mimics a cow’s uterus. The embryos are transferred to the recipient cow seven days after estrus which is the same as in traditional embryo transfer. There have been advancements in collection procedures and hormonal manipulations but there has been little focus on nutrition of the donor cow as a way to possibly increase the efficiency of IVF embryo production. It is well known by producers and feed specialists that trace minerals play an essential role in physiological functions. Minerals like copper, iodine, manganese, selenium, and zinc are important in embryonic development. Previous studies have shown a greater trace mineral concentration in animals that were fed organic trace minerals compared to those fed a similar quantity of inorganic trace minerals, possibly due to variation in absorption and utilization. Organic forms are absorbed differently because they have a metal ion bound with a carbon-based molecule while inorganic forms of trace minerals are subject to interactions that limit bioavailability. Past research has shown dairy cows supplemented with organic trace minerals had improved reproductive outcomes. The research described below was conducted to compare the efficiency of IVF collection and fertilization in cows that received either organic or inorganic trace mineral supplementation.
 
Postpartum Angus cows received either a custom formulated free choice mineral containing Zn, Cu, Mn, and cobalt glucoheptonate amino acid complexes (organic), or a custom formulated supplement of the same concentrations of trace minerals but from inorganic sources. For 90 days prior to the experiment, cows were provided a common inorganic trace mineral supplement to provide an equal starting point for mineral status. Cows were synchronized, AI’d and pregnancy tested at 28 d post-AI. Open cows were removed and not included in the IVF protocol leaving 20 cows which received organic minerals and 18 cows which received inorganic minerals. Pregnant cows were processed for IVF embryo production once on day 52 and again on day 67. Ovum pick-up was performed and follicles greater than 5 mm were aspirated to collect cumulus-oocyte complexes (COC’s), which were later placed into incubators. The COCs were washed and graded A to D for quality. Grade D COCs were discarded. In vitro fertilization was performed and the fertilized COCs cultured for 8 days.
 
The effects of organic mineral supplementation were assessed by the recovery, cleavage rate, and transferrable embryo production of COCs. Pregnancy rate was 64.71 % for cows that received complexed organic minerals and 52.90% for cows on inorganic minerals. Mineral supplement consumption was similar between groups. At day 30 the number of total COCs recovered was similar between the groups but at days 52 and 67 there were a greater number of COCs recovered from cows that received organic minerals, and a greater percentage of those COCs reached grades A through C. There were positive correlations between liver concentration of Zn or Mn and number of mature COCs. As liver concentration of Zn increased from 20 to 230 ug/ gram of dry weight, the number of mature COC’s increased from 2.07 to 8.00 per cow. When the liver concentration of Mn increased from 4.5 to 29 ug/g dry weight, the number of mature COC’s increased from 1.96 to 2.26 per cow. A similar relationship was observed with the trace mineral Co, with COC’s increasing from 2.46 to 5.20 per cow as liver Co concentration increased. Transferable and freezable embryo yields tended to be greater for the cows that received complexed trace minerals over inorganic trace minerals. Through odds ratio analysis it was concluded that cows that received organic trace mineral supplementation were 75% more likely to produce a transferable embryo than those that received inorganic minerals.
 
Physiological processes are affected by the deficiencies of trace minerals and from a reproductive standpoint, there is prolonged anestrus, decreased ovulation, decreased pregnancy rates, and increased mortality of embryos or fetuses. The concentrations of trace minerals did not differ in this experiment, but the results support the hypothesis that complexed trace minerals (organic) will aid reproductive performance. The complexed form of trace minerals increased IVF embryo production efficiency. For the producer, this suggests that replacing inorganic source trace mineral with complexed source trace mineral may be beneficial to achieve greater reproductive efficiency. The cost of IVF embryo transfer is higher than feasible for many producers; however, if using a different type of trace minerals could improve reproductive efficiency in terms of embryo collection and transfer, it may also have positive impacts on other aspects of reproductive efficiency. Further research is needed to determine if similar effects would be realized with embryo transfer, artificial insemination and natural mating.