Abstract Weaning is one of the most stressful events for commercial pigs. The transition from mother’s milk (animal proteins) to a solid diet based on plant proteins, the reduction in lactose intake and the decline in HCl secretion by the digestive system of the piglet result in a sudden and significant increase in stomach pH as well as an increased risk of post-weaning diarrhea. The aim of this trial was to evaluate whether the use of a blend of medium-chain fatty acids (MCFAs) on top-off conventional nursery diets would improve zootechnical performance and intestinal problems in just-weaned piglets. Piglets [n = 624, 21-d of age, 6.5 kg body weight (BW), (♂ Fast Duroc x ♀ Fast 275)] were housed in 26 pens of an experimental nursery. Each pen (24 pigs/pen, with a starting density of 3.0 ft2/pig) was equipped with a height-adjustable water sucker, a water bowl and fitted with a single feeder-bin. Females and males were allocated to each pen, according to 3 BW categories (heavy, medium, and light). During a 46-d period of trial, the piglets (13 replicated pens per treatment) were allotted to a conventional 5 phases feeding program with 2 kg/MT of chlortetracycline (22%) and 400 g/MT of tiamuline (1.78%; CON). These basal diets contained 2,500 ppm Zn in Phases #1, 2, and only 2,000 ppm Zn in phase #3. Phases #1 to 3 were also supplemented with Ca-butyrate (1 kg/MT) and a blend of protected acidifiers (1 kg/MT). The treated group consisted to the basal diet (CON) supplemented with a blend of medium-chain fatty acids (MCFAs) at 1.0 or 0.75 kg/MT for Phases #1, 2,3 and Phases #4, 5, respectively and supplying of a proprietary blend of caprylic, capric, and lauric acids. Daily feed consumption, weekly pig pen BW, dead and removed pigs and daily diarrhea evaluation index were completed. Data are analyzed by an ANOVA model including treatment and pen as fixed and random effects, respectively. Pairwise comparisons were completed with a Chi-square test. The overall results are presented in Table 1. At the end of wk 2 and 3, animals receiving MCFAs had a better average daily gain (ADG; P < 0.05) than CON. Therefore, at wk 2, 3 and 4, MCFAs animals BW were heavier than CON ones (P < 0.05). Average daily feed intake (ADFI) was not significantly different for the overall duration of the trial (P > 0.05). However, at weeks 2 and 3, MCFAs piglets had a greater ADFI than CON ones (P < 0.05). The daily diarrhea index of the MCFAs group was less than CON at wk 3 (P < 0.05). In this trial, the significant improvement of diarrhea index on just-weaned MCFAs treated piglets could explain the significant better growth during the first 3 wk of nursery.