373 Effects of Different Trace Mineral Supplementation Strategies on Liver Mineral Status and Gene Expression of At-Risk Mineral Deficient Feedlot Cattle

Abstract

Abstract Grazing lands in the western US are deficient in several trace minerals known to be critical for livestock health and performance. Mineral supplementation is often not possible since animals graze rough terrain, making mineral delivery logistically difficult. Therefore, trace minerals are often supplemented during the growing and feedlot period to maximize cattle health and production. However, morbidity and mortality rates are often greater in these mineral deficient cattle, at least in part due to their mineral deficiencies, and producers welcome input on best practices for mineral supplementation. This study aimed to evaluate how different mineral supplementation strategies affect liver mineral concentrations and abundance of mRNA involved in mineral transport in mineral deficient cattle receiving different mineral supplementation strategies. Sixty mineral deficient feedlot steers were obtained and initially stratified by weight into one of four treatment groups (n = 15): no mineral supplementation (CON); dietary mineral supplementations at industry recommended levels (DM); multimin injection at labeled dose (MM); or a combination of the MM and DM treatments (MM+DM). Treatments were given for the first 40 days of the trial and steers were fed ad libitum in pens equipped with GrowSafe bunks. Liver biopsies were conducted on days 0, 5, 10, 20, 30 and 40 to assess liver mineral concentrations of copper (Cu), manganese (Mn), selenium (Se), and zinc (Zn). Total mRNA was isolated from liver biopsies on days 0, 20, and 40 and mRNA abundance of genes involved in trace mineral transport was measured. The liver mineral data was analyzed using the PROC MIXED procedure of SAS with day as a repeated measure to evaluate the fixed effect of treatment. A series of contrasts were also conducted to determine whether mRNA abundance differed between the mineral treatments and the CON. There was a treatmentxday interaction (P < 0.05) on the Cu concentration where the MM treatment peaked at day 20 and then started to decrease towards day 40. All mineral treatments increased (P < 0.05) the liver Se concentration and mRNA abundance of zinc transporter (ZNT) 7, ZNT9, and Mn superoxide dismutase (MnSOD) compared with the CON. Steers receiving the DM treatment increased (P < 0.05) the mRNA abundance of Zrt- and Irt-like proteins (ZIP) 1, ZNT1, ZNT3, and ZNT4 compared with the CON. When compared with the CON treatment, the DM and MM+DM had a tendency (P = 0.07) to increase the abundance of divalent metal transporter 1 (DMT1) and ZNT1, as well as the liver Mn concentration. Overall, both the MM+DM and DM treatments improved mineral status by increasing liver mineral concentrations. However, the DM treatment was more effective at increasing the mRNA abundance of mineral transporters in the liver. Further research is needed to determine which pathways were influenced by an improved trace mineral status.