bioRxiv2020
Our objective was to estimate 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 gestation of Holstein heifers. Eleven pregnant Holstein heifers, 8 of which 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 an average daily gain of approximately 1.0 kg. The sampling periods were established according to the days of gestation: 145, 200, and 255 with a duration of 10 days per period. Total fecal samples were collected to estimate dry matter, organic matter, crude protein, and neutral detergent fiber digestibility. Blood samples were collected to analyze metabolites (non-esterified fatty acids, {beta}-hydroxybutyrate, urea, and glucose). Data were analyzed as a repeated measurements scheme, using MIXED procedure, with differences declared when P < 0.05. Dry matter intake expressed in kg/day increased from d-145 to d-200, and remaining stable until d-255 of gestation. The same results were observed for organic matter and crude protein intake, increasing 15.0 and 35.8% respectively. In contrast, when dry matter intake was evaluated as % body weight, we observed a decrease of 16.7% from d-200 to d-255. Days of gestation did not influence 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 days of gestation, with an increase of 11.9, 8.5, and 9.8%, respectively, when comparing d-145 with d-200. The rate of digestion of neutral detergent fiber increased from 2.0 to 3.5% h-1. Glucose levels decreased, while {beta}-hydroxybutirate and non-esterified fatty acids increased from d-145 to d-255. In conclusion, our results demonstrate a reduction in dry matter intake in % body weight due to pregnancy. It also shows an increase in total apparent digestibility through gestation, which imply a greater efficiency of use of nutrients by pregnant animals. Thus, further research is still needed to consolidate such results and to elucidate the mechanism about nutrient usage during the final third of gestation in heifers.