The milk profile of odd- and branched-chain fatty acids (OBCFA) is generating interest as a non-invasive method for evaluating rumen function. Synthesis by rumen microorganisms is the primary source of milk OBCFA and different groups of rumen bacteria synthesize distinct categories of OBCFA. Sub-acute ruminal acidosis (SARA) is a highly prevalent and costly disease that engenders modifications in rumen bacterial populations, which could be identified by tracking changes in milk OBCFA and how they relate to rumen bacterial groups. The increase of DCAD may alleviate the effects of acidogenic diets, whereas the supplementation of soybean oil (SBO) in the diet may exacerbate them. This trial aimed to determine the length of time required for milk OBCFA to respond to the consumption of an acidogenic diet and to evaluate the effects of DCAD, adjusted using dietary K₂CO₃, and SBO supplementation on the evolution of the milk OBCFA profile. Twenty-eight early lactation Holstein dairy cows (39 ± 9 DIM) were used in a randomized complete block design with a 2 × 2 factorial arrangement of treatments. Cows were fed a high-risk SARA diet of 40% forage (58% corn silage) and 60% concentrate, with 0 or 1.5% K₂CO₃ (DM basis), and 0 or 2% SBO. Collection period lasted 3 weeks, and samples were taken on d 1, 4, 7, 10, 14, and 17. Effects of time (repeated measures), K₂CO₃, SBO, and their interactions were evaluated and contrasts declared significant at P < 0.05. Milk iso 13:0 and iso 17:0 concentrations increased linearly after cows began receiving the acidogenic diets. Similarly, milk concentrations of 5:0, 7:0, 9:0, 11:0, 13:0, and 15:0 increased linearly over time. A 3-way interaction was also significant for 15:0. In contrast, concentrations of iso 14:0, iso 16:0, and iso 18:0 in milk decreased linearly over time. No time or treatment effects were observed for anteiso fatty acids. The common temporal pattern of changes within groups of OBCFA, and the differences between groups indicate distinct origins of OBCFA. Overall, the results show that milk OBCFA respond to the consumption of an acidogenic diet within 3 weeks.