Effects of nutrient supply and dietary bulk on O2 uptake and nutrient net fluxes across rumen, mesenteric- and portal-drained viscera in ewes1

Abstract

We assessed the effects of nutrient supply and dietary bulk, both increasing with hay intake, on O2 uptake and nutrient net fluxes across the portal-(PDV) and mesenteric- (MDV) drained viscera, and the rumen in adult ewes. Four ewes, fitted with a ruminal cannula, with catheters in the mesenteric artery, the portal, mesenteric and right ruminal veins, and with a blood flow probe around the right ruminal artery, were used in a 4 x 4 Latin square design. Treatments consisted of 500 g DM/d hay (LL, low bulk and low nutrient supply), 500 g DM/d hay + infused nutrients (LH, low bulk and high nutrient supply), 750 g DM/d hay + infused nutrients (MH, medium bulk and high nutrient supply), and 1,000 g DM/d hay (HH, high bulk and high nutrient supply). Infused nutrients consisted of volatile fatty acids (VFA) and casein dissolved in salts and infused continuously in the rumen to provide the same amount of metabolizable energy (7.6 MJ/d) and digestible protein (63 g/d) for LH, MH, and HH. Both increases in bulk and nutrient supply increased O2 uptake in the MDV and PDV. Dietary bulk stimulated mainly blood flow, whereas nutrient supply stimulated mainly O2 extraction rate. The O2 uptake by the rumen was not significantly affected by hay intake, although blood flow increased due to nutrient supply. Increase in hay intake had no effects on portal net release of lactate and net uptake of glucose but increased VFA, 3-D-hydroxybutyrate, ammonia, and amino acids (AA) net release and urea net uptake across PDV. The increase in portal nutrient net fluxes with hay intake was entirely related to the increase of nutrient supply for VFA, 3-D-hydroxybutyrate, ammonia, and urea, irrespective of the amount of casein infused for AA. Dietary bulk had no effect on total energy net release in the portal vein. We conclude that despite the increase in portal O2 uptake, increasing dietary bulk had no significant impact on portal recovery of energy. In ruminal tissues, which were the main site of energy absorption, O2 uptake appeared low and was not sensitive to dietary manipulation. In contrast, in mesenteric tissues, which contribute poorly to energy absorption with forage diets, O2 uptake appeared high and very sensitive to dietary manipulation.

Responses of hepatic blood flows to changes in intake in sheep: a meta-analysis

“…On average during the day this increase seems to be related primarily to a bulk effect of feed intake rather than the nutrient supply (Han et al, 2002). In agreement with these findings, the present results showed that compared with DMI, MEI did not improve the quality of the fit (based on r.m.s.e.…”

Digestion and nutrient net fluxes across the rumen, and the mesenteric- and portal-drained viscera in sheep fed with fresh forage twice daily: net balance and dynamic aspects

“…The rumen and MDV blood flows observed in the present experiment accounted for 18 and 23 % of the PBF, respectively. The rumen contribution to PBF is within the range of reported values (from 13 to 22 %; Barnes et al 1983;Rémond et al 2000b;Han et al 2002). The MDV contribution is in agreement with previous studies in sheep, where BF in the cranial mesenteric vein (upstream of the junction with the ileocaecocolic vein) was recorded with transittime ultrasonic probes (Neutze et al 1994;Rémond et al 2000b) or with the microsphere technique (Barnes et al 1983).…”

“…The MDV contribution is in agreement with previous studies in sheep, where BF in the cranial mesenteric vein (upstream of the junction with the ileocaecocolic vein) was recorded with transittime ultrasonic probes (Neutze et al 1994;Rémond et al 2000b) or with the microsphere technique (Barnes et al 1983). However, a greater contribution (45 % of PBF) was observed by MacRae et al (1997b) using the dye dilution technique; such a contribution was more generally attributed to the whole intestine (Neutze et al 1994;Han et al 2002).…”

“…This discrepancy could be partly explained by the large difference in MDV contribution to PBF observed between the study from MacRae et al (1997b) and the studies from our group. Nevertheless, all the studies in which PDV and MDV net flux of free EAA were recorded (Seal & Parker, 1996;MacRae et al 1997b;Rémond et al 2000b;Berthiaume et al 2001;Han et al 2002) highlighted the widespread use of arterial essential FAA by non-MDV tissues (22 -45 % of the MDV net release). In the present work, the net uptake of EAA by the rumen wall accounts for 30 % of this non-MDV uptake.…”

Effect of dry matter intake on visceral organ mass, cellularity, and the protein expression of ATP synthase, Na+/K+-ATPase, proliferating cell nuclear antigen and ubiquitin in feedlot steers

“…Increasing DMI increased not only nutrient supply but also dietary volume. Based on the research of Han et al (2002), dietary bulk stimulated portal-drained viscera blood flow whereas nutrient supply stimulated mainly O 2 extraction by the portal-drained viscera. An increased blood flow, as a result of increased dietary volume, may stimulate heart growth since workload is related to organ size (Sainz and Bentley 1997).…”