Net hepatic release of glucose from precursor supply in ruminants: a meta-analysis

Abstract

For their glucose supply, ruminants are highly dependent on the endogenous synthesis in the liver, but despite the numerous studies that evaluated hepatic glucose production, very few simultaneously measured hepatic glucose production and uptake of all precursors. As a result, the variability of precursor conversion into glucose in the liver is not known. The present study aimed at investigating by meta-analysis the relationships between hepatic glucose net release and uptake of precursors. We used the FLuxes of nutrients across Organs and tissues in Ruminant Animals database, which gathers international results on net nutrient fluxes at splanchnic level measured in catheterized animals. Response equations were developed for intakes up to 41 g DM intake/kg BW per day of diets varying from 0 to 100 g of concentrate/100 g DM in the absence of additives. The net hepatic uptake of propionate, α-amino-N and l-lactate was linearly and better related to their net portal appearance (NPA) than to their afferent hepatic flux. Blood flow data were corrected for lack of deacetylation of the para-aminohippuric acid, and this correction was shown to impact the response equations. To develop response equations between the availability of precursors (portal appearance and hepatic uptake) and net glucose hepatic release, missing data on precursor fluxes were predicted from dietary characteristics using previously developed response equations. Net hepatic release of glucose was curvilinearly related to hepatic supply and uptake of the sum of precursors, suggesting a lower conversion rate of precursors at high precursor supply. Factors of variation were explored for the linear portion of this relationship, which applied to NPA of precursors ranging from 0.99 to 9.60 mmol C/kg BW per h. Hepatic release of glucose was shown to be reduced by the portal absorption of glucose from diets containing bypass starch and to be increased by an increased uptake of β-hydroxybutyrate indicative of higher body tissue mobilization. These relationships were affected by the physiological status of the animals. In conclusion, we established equations that quantify the net release of glucose by the liver from the net availability of precursors. They provide a quantitative overview of factors regulating hepatic glucose synthesis in ruminants. These equations can be linked with the predictions of portal absorption of nutrients from intake and dietary characteristics, and provide indications of glucose synthesis from dietary characteristics.

Mismatch of Glucose Allocation between Different Life Functions in the Transition Period of Dairy Cows

“…Accordingly, the nonlinear character of the relationship between milk yield and body weight suggest an optimum body weight beyond which the feed-efficiency decreases in specialized breeds [33]. Loncke et al (2020) recently showed a similar pattern for the efficiency of hepatic glucose synthesis (conversion rate of precursors to glucose), which decreases at high levels of precursor supply [34]. As a result, high-producing dairy cows show increased rates of energy mobilization from body tissues to bridge the gap between the supply of energy from feedstuffs and the energy needed to support milk production along with all other energy-demanding life functions [35].…”

Dietary protein oscillation: Effects on feed intake, lactation performance, and milk nitrogen efficiency in lactating dairy cows

“…Lower milk and milk protein yields for OS cows compared with ST cows at M4 and a trend for lower milk and milk protein yields at M5 (Figure 4) indicated that the OS-L diet affected milk yield with a delay of approximately 48 h from initial feeding, whereas a lag of about 36 h occurred before milk protein yield was increased (at M7; tendency) on the OS-H diet. A trend for reduced milk lactose yields at M4 and M5 for OS cows may be explained by a reduced metabolizable protein supply with the OS-L diet, resulting in reduced rates of hepatic AA deamination, gluconeogenesis, and lactose synthesis (Daniel et al, 2016;Loncke et al, 2020). This is supported by lower MU at M3 and M4 and higher MU at M6, M7, and M8 for OS cows compared with ST cows (Figure 3).…”

Review: Use and misuse of meta-analysis in Animal Science

“…A systematic study of IF allows one to gain more knowledge from the data. Some examples of this approach can be found in the literature (Loncke et al 2009(Loncke et al , 2015(Loncke et al and 2020Agastin et al 2014). In the meta-analysis of Loncke et al (2015), response equations to predict hepatic uptake/release of ketogenic nutrients in response to their supply to the liver were obtained using published data from the FLORA database (FLuxes of nutrients across Organs and tissues in Ruminant Animals; Vernet and Ortigues-Marty, 2006).…”

“…In this meta-analysis, the study of IF revealed that response equations were significantly affected by other nutrients or by diet characteristics. For example, it was shown that the hepatic release of glucose was related to the net portal appearance of nitrogen (Loncke et al, 2020), but for a same level of nitrogen (LSMeans), the release of glucose increased logically with the dietary starch concentration.…”

“…In general, it is necessary to consider all factors and variables as potential IF and to test their influence on the parameters (LSMeans, residuals and within-study slopes); Loncke et al (2009Loncke et al ( , 2015Loncke et al ( and 2020 tested about 50 IFs for each equation published. The major objective of the analysis of potential IF aims to evaluate if the main independent variables (i.e.…”