Experiments were conducted to evaluate amino acid and fatty acid nutrition in beef cattle. Objectives of experiment I were to determine in situ disappearance of hay and a ruminally undegradable protein (RUP) supplement in beef cattle fed restricted amounts of forage. Cattle were fed at one of three percentages of maintenance (30%, 55%, 80%). Estimates of RUP were 49.2, 56.5, and 59.1% for 30, 55 and 80% of maintenance intake, respectively. Restricting intake can reduce dietary protein that escapes ruminal degradation. The objectives of experiment II were to determine intestinal supply of essential amino acids when consuming restricted amounts of forage plus RUP supplement. Cattle fed below maintenance were given increasing amounts of RUP supplement to equalize duodenal essential AA flow to cattle fed 105% of maintenance. Total duodenal essential AA flow did not differ ( P = 0.39) across level of intake. Balancing intestinal essential AA supply in beef cattle can be accomplished with RUP supplementation. In experiment III, objectives were to evaluate site and extent of nutrient disappearance in cattle fed safflower seeds differing in 18C fatty acids. Nine heifers were fed hay and either low-fat control or high-linoleate or high-oleate safflower seed. Total flow of unsaturated fatty acid to the duodenum was greatest ( P < 0.001) in cattle fed safflower seeds and duodenal flow of 18:1 and 18:2 increased ( P < 0.001) in Oleate and Linoleate, respectively. Experiment IV and V were conducted to determine the effects of high-linoleate safflower seeds on fatty acid composition of tissues (Exp. IV) and follicular development and hormone concentrations of postpartum cows (Exp. V). Cows were fed millet hay and either low-fat control supplement or a supplement containing high-linoleate safflower seeds. Fatty acid concentrations differed ( P < 0.05) between uterine tissue types. The provision of supplemental linoleic acid increased (P = 0.01) prostaglandin metabolite production compared to Control during the early postpartum period. Safflower seeds increased concentrations of FSH in the anterior pituitary gland (P = 0.02) and lowered concentrations of IGF-I in the median basal hypothalamus (P = 0.05). Overall, an understanding of rumen metabolism is essential for optimal animal productivity.