Effects of Dietary Additives on B-Vitamin Production and Absorption in Steers

Abstract

Eight Hereford-cross steers (470 kg), each with T cannulae in the duodenum and ileum, were used in four trials to measure effects of monensin and chlortetracycline on thiamin, niacin, riboflavin and biotin production and absorption. Steers were fed at 2-h intervals and Cr-EDTA and acid-insoluble ash were used as markers. Diets were fed in pelleted form. Effects of monensin were tested (trial 1) using a diet that contained 90% corn + 22 mg monensin/kg feed. Feed, duodenal and ileal quantities of thiamin in steers fed the basal diet were 12.6, 7.4 and .8 mg/d, respectively. Steers fed the monensin diet had thiamin quantities of 14.0, 9.3 and 1.7 mg/d for the three sites. Dietary niacin quantities did not differ among diets; however, duodenal, ileal and fecal quantities of niacin were lower in monensin-fed animals. Riboflavin and biotin quantities were not affected by monensin supplementation. Apparent ruminal organic matter digestibility was lower for steers fed monensin. In trial 2, chlortetracycline (7.8 mg/kg diet) did not affect quantities of duodenal or ileal thiamin. Chlortetracycline tended to reduce flow of niacin to the duodenum. Duodenal or ileal riboflavin was not affected by feeding chlortetracycline. In trial 3, chlortetracycline (70 mg·head−1 ·d−1) did not affect duodenal quantities of thiamin, but increased ileal (P<.01) and fecal (P<.10) quantities of thiamin. Chlortetracycline did not affect quantities of duodenal or ileal niacin or riboflavin. Quantities of riboflavin were greater in feces of control steers than in steers fed chlortetracycline. In trial 4, effects of feeding chlortetracycline (1 g/d) for 3 d were investigated during the post-antibiotic feeding period. Samples were collected on d 1 and 2, 5 and 6, and 9 and 10 following withdrawal of chlortetracycline feeding (samples from adjacent days were pooled). Chlortetracycline resulted in increased quantities (P<.005) of duodenal thiamin during d 1 and 2 (13.7 vs 6.7 mg/d). This effect decreased with time. Chlortetracycline tended (P<.25) to decrease duodenal, ileal and fecal riboflavin throughout the collection period. Niacin and biotin quantities at the various sites were not greatly affected by feeding chlortetracycline in this manner.