found no advantages to supplementing VA to cattle grazing summer pasture. Kohlmeier and Burroughs (1970) observed that most cattle entering the feedlot from grazing situations have sufficient VA reserves to meet VA requirement
for 90–120 days and suggested that no supplemental VA was needed, provided that plasma concentrations of VA remained higher than 250 ng/mL and liver concentrations remained higher than 2000 ng/g. Retinoic acid concentrations in plasma for all treatments in the present study were slightly lower than the 250 ng/mL threshold but liver retinoic acid concentrations for all treatments were well above the 2000 ng/g threshold. Knight, Death, Muir, Ridland, and Wyeth (1996