BIOAVAILABILITY OF NIACIN FROM FEED INGREDIENTS COMMONLY USED IN FEEDS FOR CHANNEL CATFISH, ICTALURUS-PUNCTATUS

A catfish bioassay for available niacin was developed using liver NAD levels as the response measure. Triplicate groups of fingerling channe l catfish were fed 7 different feed ingredients as the sole source of dietary niacin in a basal casein-gelatin diet for 8 weeks. Three other experimental diets containing known amounts of supplemental niacin (6 , 9 and 12 mg/kg diet, respectively) were also fed to triplicate group s of fish to establish the levels of NAD in the liver after 8 weeks. A standard linear regression equation of available niacin in diet (y in mg/kg) as a function of liver NAD concentration (x in mu mol/g) was d erived and used to determine the amount of available niacin in the fee d ingredients. Menhaden fish meal (MFM), meat and bone/blood meal (MBM ), wheat middlings (WML), cooked corn (CCO), uncooked corn (UCO), cott onseed meal (CSM) and soybean meal (SBM) contained 105.3, 50.5, 153.3, 21.9, 12.8, 22.5 and 20.3 mg/kg of available niacin, respectively. Wh en compared to the total niacin content of each feed ingredient, niaci n in animal tissue (MFM, MBM) was totally available to channel catfish . Availability of niacin in cereals and cereal byproducts, WML, CCO an d UCO, was about 60, 44 and 28%, respectively. Niacin availability in the two oilseeds, CSM and SBM, was found to be 58 and 57%, respectivel y. Niacin availability from corn was increased by about 57% when the c orn was extrusion-cooked. It was concluded that supplementation of nia cin may not be needed or can be lowered in typical commercial catfish feeds because of the relatively high amount of available niacin found in the feed ingredients. (C) 1998 Elsevier Science B.V.