tTwo in vitro experiments were conducted to evaluate the interactions of monensin with lau-ric acid distillate (LAD) or palm oil (PO) in forage and concentrate diets on 24 h in vitro rumenfermentation characteristics. Two Holstein steers, each surgically fitted with a ruminal can-nula, consuming 0.50 alfalfa cubes and 0.50 cracked corn-based concentrate at 1.75 × NEmrequirements were used as rumen fluid donors.