Metabolic effects of safflower oil given as a supplement for steers fed roughage diets at restricted intake

Abstract

Supplements of safflower oil (300 mL/day) were given to groups of steers fed 4 different diets. Hereford steers were fed 6 kg/day lucerne hay (LH) or LH + 33 mg/kg monensin (LHM). Brahman steers were fed 4 kg/day low quality hay (DA) or DA + 1 kg sucrose + 60 g urea + 2.7 g sulfur (DAS). Metabolic measurements were made when the animals were fed an equal portion of the daily ration at hourly intervals. On all diets, safflower oil had no affect on rumen temperature, pH or the concentrations of volatile fatty acids in ruminal fluid. Safflower oil increased concentrations (mg/L) of microbial lipid in ruminal fluid (LH, 160.4 v. 317.1; LHM, 266 v. 541.7; DA, 194.6 v. 321.8; DAS, 172.8 v. 440.5) and increased plasma concentrations (�g/mL) of non-esterified fatty acids (LH, 117.2 v. 180.1; LHM, 101.1 v. 189.5; DA, 218.2 v 325.4; DAS, 197.4 v 311.4), especially 18:1 trans- 11 and polyunsaturated acids. In steers fed DA and DAS, safflower oil reduced protozoal numbers and increased the bacterial mass in ruminal fluid, and increased water intake and the daily amounts of urinary allantoin excreted. The addition of safflower oil to all diets depressed plasma urea concentrations (mg/L) (LH, 233 v. 203; LHM, 236 v. 191; DA, 74.6 v. 47.6; DAS, 96.6 v. 54). The excretion of daily amounts (mg/kg liveweight) of urinary urea increased in animals fed DA (3.5 v. 10.0) and DAS (6.2 v. 13.6) but decreased in those fed LH (208.8 v. 187.9) and LHM (188.8 v. 158.1). Safflower oil supplementation conserved body protein, accelerated liveweight gains in animals fed LH and LHM diets and retarded liveweight loss in those fed DA and DAS diets.