The objectives of this study were 1) to quantify daily patterns of plasma flow and metabolite flux through portal-drained viscera (PDV) and liver in cattle fed twice daily and 2) to identify an interval for blood sampling that would approximate the average daily plasma flow and nutrient flux values. Data are from three experiments in which multicatheterized cattle were fed at or near ad libitum intake twice daily. Five lactating primiparous Holstein cows (506 kg, fed at 0730 and 1930) ate 17.3 kg DM/d as chopped alfalfa hay:corn grain plus supplement (urea and minerals) 50:50 (Exp 1). Five beef steers (474 kg, fed at 0900 and 2100) ate 8.3 kg DM/d as chopped switchgrass hay:corn grain plus supplement 37:63 (Exp 2). Six beef steers (306 kg fed at 0900 and 2100) ate 6.9 kg DM/d as chopped alfalfa hay (Exp 3). Plasma flow (by dilution of para-aminohippurate) was measured hourly for 24 h. Plasma flows (mean +/- SE) through PDV were 1,264 +/- 147, 538 +/- 56, and 499 +/- 26 L/h for Exp. 1, 2, and 3, respectively. Corresponding liver flows were 1,662 +/- 216, 642 +/- 41, and 591 +/- 30 L/h. The within-animal differences from their respective daily means were estimated as a function of time of day using nonparametric smoothing. Across experiments, PDV and liver flows were above the daily mean from 1200 to 1400, were not different from the daily mean from 1600 to 1700, and were below the daily mean from 1930 to 2130. Metabolites measured were ammonia, urea, alpha-amino N, and glucose. In general, metabolite flux was not different from the average daily mean values between 1200 and 1600. Blood sampling over 12 h or one 12-h feeding cycle is sufficient for daily plasma flow and metabolite flux estimation in cattle fed twice daily.

(Huntington, 1984).No variation in intake, milk yield and composition was observed during the infusion of propionate. It resulted in an increase (P < 0.05) in arterial concentration of proprionate (+ 25%) and an astonishing slight decrease (P < 0.1 ) in glucose production (-11%) by the splanchnic tissues. This loss in carbon source for the peripheral tissues is partially filled (55%) by the greater release of lactate, alanine and other sources to these tissues. Part of the decrease in urea production could be explained by the lesser amino acid desamination (hepatic alanine/urea = -60%). Glucose and urea metabolisms are energy users; the decrease of these activities in the liver could account for the overall decrease in splanchnic oxygen consumption.

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An experiment was conducted to study the effects of a chronic physiological infusion of sodium proprionate, in the mesenteric vein, on liver and portal drained viscera (PDV) metabolisms of dairy cows. Four multicatheterized (Huntington et al, 1989), high producing (32 t 2 kg milk/d), first lactating dairy cows (520 ± 11 kg of body weight) were used during their 5th and 6th month of lactation. They were milked twice a day and fed ad libitum a diet of 50% alfalfa hay and 50% concentrate (21 ± 1 kg DM/d, 55 t 2 Mcal ME/d, 538 g N/d). Each animal received both control (NaCI) and propionate treatment, for 72 h (NaC 3 : 1 ml/min of a 2.5 M solution), in a reversal design. Simultaneous blood samples (10 samples/cow, every 20 min, 3 h after the morning meal) were withdrawn from artery, hepatic vein and portal vein. Blood flow was determined with dye dilution (Huntington, 1984). No variation in intake, milk yield and composition was observed during the infusion of propionate. It resulted in an increase (P < 0.05) in arterial concentration of proprionate (+ 25%) and an astonishing slight decrease (P < 0.1) in glucose production (-11%) by the splanchnic tissues. This loss in carbon source for the peripheral tissues is partially filled (55%) by the greater release of lactate, alanine and other sources to these tissues. Part of the decrease in urea production could be explained by the lesser amino acid desamination (hepatic alanine/urea =-60%). Glucose and urea metabolisms are energy users; the decrease of these activities in the liver could account for the overall decrease in splanchnic oxygen consumption .