Effect of palmitic acid-enriched supplements containing stearic or oleic acid on nutrient digestibility and milk production of low- and high-producing dairy cows.

We evaluated the effects of fatty acid (FA) supplement blends containing 60% palmitic acid (C16:0) and either 30% stearic acid (C18:0) or 30% oleic acid (cis-9 C18:1) on nutrient digestibility and milk production of low- and high-producing dairy cows. Twenty-four multiparous Holstein cows [118 ± 44 d in milk (DIM)] were divided into 2 blocks by milk production and then randomly assigned to treatment sequence in four 3 × 3 Latin squares within production level, balanced for carryover effects in three consecutive 21-d periods. Cows were blocked by milk yield and assigned to 1 of 2 groups (n = 12 per group): (a) low group (42.5 ± 3.54 kg/d; 147 ± 42 DIM) and (b) high group (55.8 ± 3.04 kg/d; 101 ± 34 DIM). Commercially available fat supplements were combined to provide treatments that consisted of the following: (1) control (CON; diet with no supplemental FA), (2) FA supplement blend containing 60% C16:0 and 30% C18:0 (PA+SA), and (3) FA supplement blend containing 60% C16:0 and 30% cis-9 C18:1 (PA+OA) The FA blends were fed at 1.5% of dry matter (DM) and replaced soyhulls from CON. Preplanned contrasts were (1) overall effect of FA treatments [CON vs. the average of the FA treatments (FAT); 1/2 (PA+SA + PA+OA)], and (2) effect of FA supplement (PA+SA vs. PA+OA). Regardless of production level, overall FAT reduced DMI compared with CON. Also, regardless of level of milk production, PA+OA increased total-tract FA digestibility compared with PA+SA. Treatment by production level interactions were observed for neutral detergent fiber (NDF) digestibility, total FA intake, and the yields of 3.5% fat-corrected milk (FCM), energy-corrected milk (ECM), and milk fat. In low-producing cows, FAT increased DM and NDF digestibility compared with CON. In high-producing cows PA+SA increased DM and NDF digestibility compared with PA+OA. In low-producing cows, PA+SA increased 3.5% FCM, ECM, and milk fat yield compared with PA+OA. However, in high-producing cows PA+OA tended to increase 3.5% FCM compared with PA+SA. In conclusion, low-producing cows responded better to a FA blend containing 60% C16:0 and 30% C18:0, whereas high-producing dairy cows responded more favorably to a FA blend containing 60% C16:0 and 30% cis-9 C18:1. However, further research is required to validate our observations that higher-yielding cows have improved production responses when supplemented with cis-9 C18:1 compared with C18:0.

NMR characterization of surface interactions in the cytochrome b5-cytochrome c complex.

The complex formed in solution by native and chemically modified cytochrome c with cytochrome b5 has been studied by 1H and 13C nuclear magnetic resonance spectroscopy (NMR). Contrary to predictions of recent theoretical analysis, 1H NMR spectroscopy indicates that there is no major movement of cytochrome c residue Phe82 on binding to cytochrome b5. The greater resolution provided by 13C NMR spectroscopy permits detection of small perturbations in the environments of cytochrome c residues Ile75 and Ile85 on binding with cytochrome b5, a result that is in agreement with earlier model-building experiments. As individual cytochrome c lysyl residues are resolved in the 1H NMR spectrum of N-acetimidylated cytochrome c, the interaction of this modified protein with cytochrome b5 has been studied to evaluate the number of cytochrome c lysyl residues involved in binding to cytochrome b5. The results of this experiment indicate that at least six lysyl residues are involved, two more than predicted by static model building, which indicates that cytochrome c and cytochrome b5 form two or more structurally similar 1:1 complexes in solution.