Gibb, D. J., Van Herk, F. H., Mir, P. S., Loerch, S. and McAllister, T. A. 2011. Removal of supplemental vitamin A from barley-based diets improves marbling in feedlot heifers. Can. J. Anim. Sci. 91: 669-674. The objective of this research was to determine if removing supplemental vitamin A from barley-based feedlot diets affects animal performance, health, or carcass quality. Six pens per treatment (10 heifers per pen) were randomly assigned to receive zero (-VA) or 3640 ( VA) IU kg-1 dry matter of supplemental vitamin A in barley-based feedlot diets. Initial serum retinol was similar between treatments (28 µg dL-1; P=0.34), but -VA reduced levels by 40% (30 vs. 50 µg dL-1; P<0.001) by day 217. Removal of supplemental vitamin A reduced dry matter intake during the 58 d backgrounding period (6.93 vs. 7.07 kg d-1; P=0.007) and over the 218-d trial (9.18 vs. 9.35 kg d-1; P<0.001), but had no effect on average daily gain during backgrounding (1.22 kg d-1; P=0.46) or over all (1.46 kg d-1; P=0.15). Based on camera grading, -VA increased degree of marbling (480.6 vs. 439.3; P=0.02) without affecting backfat thickness (0.74 cm; P=0.62). Ultrasound measurements were highly correlated with camera grading, but did not detect treatment difference in marbling score (P=0.99). Results from this study show that the removal of supplemental vitamin A increased marbling without affecting backfat, gains, or animal health.
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