THE FOLIC-ACID REQUIREMENTS OF STARTING BROILER CHICKS FED DIETS BASED ON PRACTICAL INGREDIENTS .1. INTERRELATIONSHIPS WITH DIETARY CHOLINE

Five experiments were conducted to evaluate the effect of dietary supp lemental folic acid in starting broiler chick diets. In the first two experiments, basal diets based on corn and soybean meal contained 10 m u g/kg vitamin B-12 but no supplemental methionine or choline. Chicks showed curvilinear responses to folic acid supplementation with maximu m growth and feed efficiencies from 1.45 mg/kg diet. The liver folic a cid response was also curvilinear but reached a plateau at 1.70 mg fol ic acid/kg diet. The basal diet for three additional experiments conta ined soybean meal that had been washed with methanol to remove most of the choline. The basal diet contained only 750 mg/kg choline. Chicks exhibited a larger growth response to folic acid at low choline levels as evidenced by a significant folic acid by choline interaction. Chol ine and folic add both increased tibia length and width. Folic acid su pplementation increased but then decreased valgus deformity. Choline c hloride supplementation also decreased the incidences of valgus and va rus deformities and decreased bone ash, but increased the incidence of tibial dyschondroplasia. It is concluded that chicks fed practical in gredient-based diets require 1.3 mg folic acid/kg diet with low levels of choline, but only 1.2 mg folic acid/kg when choline is offered nea r the NRC recommended level of 1,300 mg/kg of choline.