Rumen degradable protein levels on fatty acid profile of rumen bacteria and milk fat of dairy cows supplemented with calcium salts of fatty acids

Abstract This study aimed to evaluate the effects of calcium salts of fatty acids (CSFA) from soybean oil in diets with different levels of rumen degradable protein (RDP) on bio‐hydrogenation extent, and fatty acid (FA) profile intake, omasal digesta, rumen bacteria, and milk fat. Eight Holstein lactating cows were used in a replicated 4 × 4 Latin square design. Treatments were arranged in a 2 × 2 factorial design with two CSFA levels (0 or 33.2 g/kg DM of CSFA) and two RDP levels (98.0 or 110 g/kg DM). There was RDP and CSFA interaction effect on the omasal flow of total FA and some specific FA. Only in −CSFA diets, the higher RDP level increased omasal flow of total FA. Dietary RDP levels did not affect the FA profile of bacteria and milk fat. Feeding CSFA reduced or tended to reduce the bacterial proportion of C15:0, C16:0, C16:1, C17:0, and C18:0 FA and decreased the concentrations of short‐ and medium‐chain FA (<18C) and increased the concentrations of unsaturated and long‐chain FA (≥18C) in milk fat. Feeding CSFA of soybean oil increases the intake and omasal flow of FA and augments unsaturated FA content in bacteria pellets and milk fat.