Effect of Changing the Proportion of C16:0 and Cis-9 C18:1 in Fat Supplements on Rumen Fermentation, Glucose and Lipid Metabolism, Antioxidation Capacity, and Visceral Fatty Acid Profile in Finishing Angus Bulls

This study evaluated the effects of different proportions of palmitic (C16:0) and oleic (cis-9 C18:1) acids in fat supplements on rumen fermentation, glucose (GLU) and lipid metabolism, antioxidant function, and visceral fat fatty acid (FA) composition in Angus bulls. The design of the experiment was a randomized block design with 3 treatments of 10 animals each. A total of 30 finishing Angus bulls (21 ± 0.5 months) with an initial body weight of 626 ± 69 kg were blocked by weight into 10 blocks, with 3 bulls per block. The bulls in each block were randomly assigned to one of three experimental diets: (1) control diet without additional fat (CON), (2) CON + 2.5% palmitic calcium salt (PA, 90% C16:0), (3) CON + 2.5% mixed FA calcium salts (MA; 60% C16:0 + 30% cis-9 C18:1). Both fat supplements significantly increased C18:0 and cis-9 C18:1 in visceral fat (P < 0.05) and up-regulated the expression of liver FA transport protein 5 (FATP5; P < 0.001). PA increased the concentrations of insulin (P < 0.001) and aspartate aminotransferase (AST; P = 0.030) in bull’s blood while reducing GLU (P = 0.009) concentrations. PA increased the content of triglycerides (TG; P = 0.014) in the liver, the content of the C16:0 in visceral fat (P = 0.004), weight gain (P = 0.032), and up-regulated the expression of liver diacylglycerol acyltransferase 2 (DGAT2), stearoyl-CoA desaturase 1 (SCD1; P < 0.05). MA increased blood superoxide dismutase activity (SOD; P = 0.011), reduced the concentration of acetate and total volatile FA (VFA) in rumen fluid (P < 0.05), and tended to increase non-esterified FA (NEFA; P = 0.069) concentrations in blood. Generally, high C16:0 fat supplementation increased weight gain in Angus bulls and triggered the risk of fatty liver, insulin resistance, and reduced antioxidant function. These adverse effects were alleviated by partially replacing C16:0 with cis-9 C18:1.