PSXIV-1 Trace mineral supplementation of beef cows.

Abstract Grazing cattle usually has deficiencies in trace minerals leading to productive and reproductive problems. Therefore, the objective of this research was to evaluate a liquid trace mineral supplement for grazing cows. A previous mineral study of soil, water, forages and cows from a farm in the semi-arid region of México demonstrated copper and zinc deficiencies, and manganese excess. An oral drench (G1) that included copper, iodine, cobalt, zinc and selenium was formulated. It provided, at least, requirements of given minerals for four days. This drench was compared to injectable Multimin® 90 (G2) in an estrus synchronization protocol of fifty multiparous grazing cows. The protocol lasted nine days: on day one, the CIDR® device was placed and estradiol cypionate (2 mg) was injected. On day 7, CIDR® was withdrawn, and cows were injected with 400 IU ECG, sodium colprostenol (0.5 mg) and estradiol cypionate (1 mg). Forty-eight hours after the removal of the CIDR®, fixed-time insemination was done. G1 was given on day one and seven of the protocol, while G2 was applied 30 days before the protocol. Variables measured were mineral concentrations of copper, zinc and selenium in blood serum at days one and nine of synchronization protocol. Gestation was determined with an ultrasound Siui CTS-800® at day 35. Blood samples were centrifuged at 2500 rpm for 10 minutes to extract blood serum, which was frozen until mineral analysis. The mineral determinations were made using an atomic absorption spectrophotometry technique (PerkinElmer A700). The mineral concentrations were analyzed with the GLM and mixed procedures with 2x2 factorial arrangement (types of mineral supplements and protocol days). The mineral trajectories were determined by proc sgplot, and pregnancy rate was analyzed using the bootstrapping technique. Concentrations of copper, zinc, and selenium in cows blood serum were not affected by the supplements (p>0.05). However, blood serum copper and zinc concentrations were lower (p< 0.01) and also deficient at day 9 of the protocol vs day one. Supplemente x day interaction caused higher (p< 0.01) concentrations in cows receiving oral drench at day 9 in comparison with all treatments. The oral drench caused a smaller decrease (p< 0.05) in copper concentrations and a greater increase (p< 0.05) in selenium concentrations over time, compared to cows that received G2; while zinc was not affected (p >0.05). The best response to oral drench was probably due to closeness to the synchronization protocol and a better status was achieved for copper and selenium. Cows that received oral drench were superior in gestation rate (p=0.001) than cows injected with G2: 68 vs 40 %. Strategic supplementation with a liquid product of trace minerals, coupled to an estrus synchronization program, proved to be effective to improve pregnancy rate in beef cows.