Digestive parameters during gestation of Holstein heifers

•Digestibility increased in dairy heifers from day 145 to 200 of gestation.•Pregnant heifers increased dry matter, organic matter, and crude protein intake (14.9, 14.7, and 41.7% respectively) from 145 to 200 days in gestation, when fed for a gain of approximately 1 kg/d.•Dry matter intake in heifers expressed as a percentage of body weight, was reduced by 16.7% from day 145 to 255 of gestation. Our objective was to estimate the nutrient intake, ruminal flow, total apparent and ruminal digestibility, rates of passage and digestion, ruminal and omasal pH, blood metabolite concentrations, and body measurements during the gestation of Holstein heifers. Eleven pregnant heifers, 8 of which were fitted with a rumen cannula (450 ± 27.6 kg of body weight and 20 ± 3.5 months of initial age), were used. All heifers received the same diet composed of corn silage, soybean meal, corn meal, minerals and vitamins with a corn silage:concentrate ratio of 50:50 (on a dry matter basis), aiming for an average daily gain of approximately 1.0 kg/d. The sampling periods were established according to the days of gestation as 145, 200, and 255, with a duration of 10 days per period. Total fecal samples were collected to estimate the dry matter, organic matter, crude protein, and neutral detergent fiber digestibility. Blood samples were collected to analyze metabolites (non-esterified fatty acids, β-hydroxybutyrate, urea, and glucose). The data were analyzed by a repeated-measurements scheme using the MIXED procedure of SAS (9.4; SAS Institute Inc.). The dry matter intake expressed in kg/day increased from d-145 to d-200 and remained stable until d-255 of gestation. The same results were observed for the organic matter and crude protein intake, which increased by 15.0 and 35.8%, respectively. In contrast, when the dry matter intake was evaluated as a% body weight, we observed a decrease of 16.7% from d-200 to d-255. The days of gestation did not influence the ruminal flow of dry matter, organic matter, crude protein, and neutral detergent fiber. We observed an increase in the ruminal digestibility of neutral detergent fiber by 20.5%. The apparent total-tract digestibility of dry matter, organic matter, and crude protein changed over the days of gestation with increases of 11.9, 8.5, and 9.8%, respectively, comparing d-145 with d-200. The rate of digestion of neutral detergent fiber increased from 2.0 to 3.5% h − 1. The glucose levels decreased, while β-hydroxybutirate and non-ester