Summary
This paper combines a quantitative review of glucose metabolism in lactating ruminants with an experimental study using multi-catheterised goats and dual-isotope (³H and ¹⁴C) tracing of gluconeogenic substrates. The authors demonstrate that propionate is the dominant gluconeogenic substrate in the fed state (62% of hepatic glucose output with propionate infusion), whilst amino acid contribution varies substantially (19–36% depending on treatment), and that hormonal regulation differs between substrates, with glucagon more responsive to amino acid availability than propionate availability.
Regional applicability
The findings are directly applicable to UK dairy cattle and sheep management, as the fundamental glucose metabolism pathways and regulatory mechanisms are conserved across ruminant species. The quantitative estimates of substrate contribution to gluconeogenesis inform nutritional requirements and metabolic modelling for lactating livestock in temperate regions.
Key measures
Portal nutrient appearance, hepatic nutrient uptake, whole-body glucose flux rate, hepatic glucose output, proportional contribution of propionate and amino acids to hepatic glucose synthesis (%), portal plasma glucagon concentration
Outcomes reported
The study quantified hepatic glucose synthesis from different substrates (propionate, amino acids, lactate, glycerol) in lactating goats using continuous isotope infusion and measured nutrient exchanges across portal-drained viscera and liver. Results demonstrated differential contributions of gluconeogenic substrates to total glucose flux depending on treatment (propionate infusion versus amino acid infusion).
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