Nariño (Colombia) has high dairy potential; however, their herds present difficulties in the nutritional component (energy imbalance) of the cows, affecting their productivity. This research evaluated the effect of a bypass fat supplement on lipid concentration in milk and the reproductive efficiency of dairy cows. The study was based on 21 Holstein x Simmental cows between first and third calving and the following was supplied: forage + concentrate (T1); forage + concentrate + 250 g/day of bypass fat (T2) and forage + concentrate + 250 g/day of bypass fat enriched with omega-three (T3). The experiment was conducted from day 15 pre-calving until day 105 of lactation. During this period, milk quantity, quality, composition, and reproductive behavior were recorded. For data analysis, a repeated measure mixed design with time-series data was used, where the fixed effects were the treatments, periods, and their interaction, the animals represented the random effect, and the covariable was the estimated milk yield during lactation. The results showed normal mobilization of adipose tissue; the compositional quality of the milk did not vary across treatments, although T2 presented a higher estimated production per lactation, and T3 presented a higher percentage of fatty acid C18:2. In the reproductive indicators, they were not influenced between the treatments; concluding that the base diet offered in the herd presents a nutritional balance appropriate to the requirements of the cows in production.