The effect of a commercial feed additive on the immune-metabolic axis, liver function and predicted carcass quality in purebred Angus steers

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To determine the effect of the commercial feed additive OmniGen-AF® on immune, physiological, and carcass ultrasound variables in steers during backgrounding, transition, and finishing phases, nine purebred Angus half-sibling steers were randomly assigned to one of two treatment groups: Control (n = 4) and OmniGen-AF (OG; n = 5). Cattle were offered 0 (Control) or 56 g daily of OG throughout a 28-d backgrounding period (limit-fed a predominantly forage diet), a 14-d transition period, and a 56-d finishing period on a high concentrate diet (104 days total). During the three feeding periods, whole blood and serum was collected to evaluate markers of immune function and physiology, respectively. Across basal diet phases, OG supplementation increased serum chloride (P = 0.02) and haptoglobin (P = 0.03) concentrations and decreased serum NEFA (P = 0.001) concentrations. At the end of the high-concentrate finishing period, OG supplementation vs. Control attenuated the decrease in serum paraoxonase and the increase in AST concentrations, a marker of liver cell necrosis. Carcass prediction measurements, collected in 30-day intervals during the finishing phase, indicated lower predicted numerical yield grades (P = 0.03) due to higher REA (P = 0.009) and a tendency for less 12th rib fat (P = 0.06) in Control vs. OG steers. Weight gain, feed intake, feed efficiency, and predicted quality grades did not differ between treatments. In conclusion, OG may act on the immune-metabolic axis across the three studied basal diet phases to support healthier livers and improved predicted yield grades in Angus steers by decreasing fat deposition and increasing REA.