The use of medium-chain fatty acids (MCFA) during the periparturient period can alleviate the effects of negative energy balance and improve animal health in early lactation dairy cows. The objective of this study was to evaluate blood β-hydroxybutyrate (BHBA) of 30 early-lactation F₁ Gir × Holstein cows supplemented with MCFA. Diets were formulated according to the NRC (2001) model and contained 50% forage as corn silage and chopped sugar cane. Concentrate was based on ground corn, soybean meal, citrus pulp and minerals in 2 treatments: (1) no addition of MCFA (0FA); and (2) addition of 40 g of MCFA [40FA, 0.186% of dry matter as toplac rumacel (Nutrifarma, Taio, PR, Brazil)]. The experiment was a completely randomized design and cows were supplemented with MCFA during the periparturient period (from 21 d before parturition until 21 d after). A portable electronic diagnosis equipment (Ketovet, TaiDoc technology, Taiwan, China) was used for measurement of BHBA and results are expressed in mM. Blood was sampled from the tail artery or vein, and the volume of 1 drop was added to a reagent strip set for BHBA analysis. Samples were collected and analyzed at the day of parturition and then again after 42 and 70 d in milk. Animals with values above 1.2 mM were diagnosed with subclinical ketosis. Data were analyzed using the MIXED procedure of SAS and significance was declared at P < 0.05. At the day of parturition, 73.4% of cows in 0FA (11 out of 15) had subclinical ketosis while only 6.6% (1 out of 15 cows) of cows on 40FA had subclinical ketosis (P < 0.05). The proportion of cows with subclinical ketosis was reduced to 40% for 0FA and slightly increased to 13.4% for 40FA after 42 d in milk and this proportion remained for after 70 d in milk, being significantly different between treatments (P < 0.05). Results of this study suggests that F₁ Gir × Holstein cows receiving diets based on corn silage and chopped sugar cane supplemented with MCFA may have lower incidence of subclinical ketosis when compared with non-supplemented cows.