Addition of fatty acids (FA) and amino acid (AA) supplements to dairy cow diets is becoming common practice due to the growing demand to increase milk fat and milk protein yields. This thesis contains two studies that evaluate the effects of supplemental palmitic (C16:0) and oleic (cis-9 C18:1) acids, and methionine (Met) and lysine (Lys), on lactating dairy cows. The first experiment used a product containing 80% C16:0 + 10% cis-9 C18:1 supplied at 1.5% diet dry matter (DM) and supplemental Met and Lys in low forage diets (LF) and a control diet with no added FA or AA at typical midwestern forage content (CON). Compared with CON, LF increased dry matter intake (DMI), milk fat yield, milk protein yield, energy-corrected milk (ECM) yield, and body condition score (BCS). In the second experiment, different ratios of palmitic (C16:0) and oleic (cis-9 C18:1) acid were supplemented in basal diets containing high CP without supplemental AA (HP) or low CP with supplemental AA (LP). FA treatments were products consisting of 80% C16:0 + 10% cis-9 C18:1 (PA) and 60% C16:0 + 30% cis-9 C18:1 (OA) supplemented at 1.5% diet DM and a non-FA supplemented control diet (CON). No interactions were observed between basal diet and FA treatment for the yields of milk or milk components. Compared with HP, LP decreased milk urea nitrogen and blood urea nitrogen concentrations, and did not impact milk, milk fat, or milk protein yields. FA treatments decreased DMI and increased milk yield, fat yield, ECM yield, and feed efficiency. Results from this work can provide information that can be used as a foundation for future studies and to guide feeding decision to maximize performance and farm income.
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