20Our objective was to estimate nutrient intake, ruminal flow, total apparent and ruminal 21 digestibility, rates of passage and digestion, ruminal and omasal pH, blood metabolite 22 concentrations, and body measurements during gestation of Holstein heifers. Eleven 23 pregnant Holstein heifers, 8 of which fitted with a rumen cannula (450 ± 27.6 kg of body 24 weight and 20 ± 3.5 months of initial age) were used. All heifers received the same diet 25 composed of corn silage, soybean meal, corn meal, minerals and vitamins, with a corn 26 silage:concentrate ratio of 50:50 (on a dry matter basis), aiming an average daily gain of 27 approximately 1.0 kg. The sampling periods were established according to the days of 28 gestation: 145, 200, and 255 with a duration of 10 days per period. Total fecal samples 29were collected to estimate dry matter, organic matter, crude protein, and neutral detergent 30 fiber digestibility. Blood samples were collected to analyze metabolites (non-esterified 31 fatty acids, β-hydroxybutyrate, urea, and glucose). Data were analyzed as a repeated 32 measurements scheme, using MIXED procedure, with differences declared when P < 33 0.05. Dry matter intake expressed in kg/day increased from d-145 to d-200, and remaining 34 stable until d-255 of gestation. The same results were observed for organic matter and 35 crude protein intake, increasing 15.0 and 35.8% respectively. In contrast, when dry matter 36 intake was evaluated as % body weight, we observed a decrease of 16.7% from d-200 to 37 d-255. Days of gestation did not influence ruminal flow of dry matter, organic matter, 38 crude protein, and neutral detergent fiber. We observed an increase in the ruminal 39 digestibility of neutral detergent fiber by 20.5%. The apparent total-tract digestibility of 40 dry matter, organic matter, and crude protein changed over days of gestation, with an 41 increase of 11.9, 8.5, and 9.8%, respectively, when comparing d-145 with d-200. The rate 42 of digestion of neutral detergent fiber increased from 2.0 to 3.5% h -1 . Glucose levels 43 decreased, while β-hydroxybutirate and non-esterified fatty acids increased from d-145 3 44 to d-255. In conclusion, our results demonstrate a reduction in dry matter intake in % 45 body weight due to pregnancy. It also shows an increase in total apparent digestibility 46 through gestation, which imply a greater efficiency of use of nutrients by pregnant 47 animals. Thus, further research is still needed to consolidate such results and to elucidate 48 the mechanism about nutrient usage during the final third of gestation in heifers. 49 50 51 According to the Hoffman [1], heifers should have the first parturition with at least 52 94% of their mature body weight, considering the fetal weight. Thus, their nutritional plan 53 requires strategies to maintain constant and satisfactory gains until the end of gestation 54 [2]. According to Mohd [3] the advances in reproduction were superior to the nutritional 55 advances of heifers, producing precocious animals that may present low ...