Two experiments with dairy cows during early lactation were conducted to determine the effects of feeding feather meal and fat. The objective of Experiment 1 was to determine milk production, milk composition, feed intake, and concentrations of AA and long chain fatty acids in blood plasma. Thirty two Holstein cows began a six week trial at the start of the fourth week of lactation. Diets included a control diet (51% forage, 49% concentrate, 16.8% CP, and 19.1% ADF) and diets containing 2.2% feather meal, 3.6% supplemental fat (hydrogenated tallow), or feather meal plus fat. Feather meal and supplemental fat were substituted for soybean meal and corn grain, respectively, in the control diet concentrate. For Experiment 2, four lactating Holstein cows (15, 20, 21, and 65 d postpartum) with ruminal and duodenal cannulae were used in a 4X4 Latin square design (21 d feeding periods) to determine digestibilities of the four diets. The markers used to estimate digesta flow were Co- EDTA and chromic oxide. When cows were fed feather meal, milk fat % was higher, milk protein % was lower, and plasma total essential AA were increased. Dry matter intake, milk production, and plasma long chain fatty acids increased when cows were fed diets containing fat. Differences between concentrations of AA in the tail artery and mammary vein indicated significant uptake by the mammary gland. The mammary gland extracted approximately 36% of the total essential AA in plasma. Intake, duodenal flow, and ruminal and total tract digestibilities of DM, ADF, N, and OM were similar for all diets. No changes were seen in rumen pH, rumen ammonia-N, VFA's, or rumen bacteria AA. Intake and fecal output of total, essential, and non-essential AA were greater when cows were fed diets containing feather meal. However, flow of AA to the duodenum, AA absorbed, and AA digestibilities did not differ. Results suggest that bypass proteins with a complimentary EAA profile must be fed with feather meal to compensate for the low amounts of Lys, Met, and His provided by feather meal. / Master of Science