093 Effect of trace mineral (TM) source on postweaning Bos Taurus bull growth, performance and liver mineral status

The objective was to investigate the effect of postweaning trace mineral (TM) source on bull growth, performance and liver TM status over a 224 d period. Bulls (231 ± 4 d, 260 ± 5 kg, n = 14, 7 per TM) were blocked by sire, age and weaning BW and randomly assigned to TM source (inorganic as salt sulfates, ING; organic as Se-yeast and proteinates, ORG). Diet included cracked corn, cottonseed hulls, a protein pellet, and TM supplement pellet. Weekly BW and blood samples were collected for quantification of serum IGF-1 concentrations by RIA. Hip height (HH) and ultrasound measurements of LM area (LMA), 12th rib back fat thickness (FAT) and LM intramuscular fat percentage (IMF) were recorded every 28 d, while liver biopsies were collected every 56 d to determine TM status (Co, Cu, Fe, Mn, Mo, Se, Zn). Statistical analysis used repeated measures in PROC MIXED of SAS with fixed effects of TM, time and interaction. Growth data presented as LSM ± pooled SE. There was no effect (P > 0.31) of TM on LMA (69.18 vs. 70.25 ± 2.11 cm2), FAT (0.51 vs. 0.48 ± 0.04 cm), IMF (3.41 vs. 3.98 ± 0.39 %), BW (385 vs. 387 ± 17 kg), BCS (5.06 vs. 5.01 ± 0.08) HH (118.7 vs. 118.0 ± 1.4 cm) and ADG (1.25 vs. 1.28 ± 0.09 kg), for ING and ORG, respectively. Throughout the trial, bull LMA, FAT, BW, BCS, HH, ADG and IGF-1 increased (P < 0.01), while IMF remained unchanged (P = 0.56). Concentrations of IGF-1 did not differ (P = 0.14) for ORG compared to ING (182.2 vs. 126.5 ± 25.0 ng/mL, respectively). A TM × time effect (P < 0.01) occurred for IGF-1. On d 0, ING (52.7 ± 30.4 ng/mL) and ORG (56.4 ± 30.4 ng/mL) had similar IGF-1, but ORG (198.3 ± 30.6 ng/mL) had greater IGF-1 compared to ING (149.7 ± 29.7 ng/mL) on d 224. Liver TM concentrations were not (P > 0.11) affected by TM source, but were affected (P < 0.01) by time and increased from trial start in all bulls. Bull performance was not affected by TM source; although, IGF-1 concentrations were increased over time in ORG compared to ING bulls.