The challenge is not merely to supply energy, but to use it efficiently

Genetic selection has dramatically increased the growth rate of broilers. Reaching more than 2 kg of body weight in 35 days requires close coordination between nutrient digestion and absorption, hepatic nutrient metabolism, protein synthesis and continuous ATP production. Under these conditions, even small differences in metabolic efficiency may result in meaningful changes in growth, feed conversion ratio and cost per kilogram of body weight produced.

Conventional feed formulation addresses this demand by increasing dietary metabolizable energy, primarily through cereals and fats. However, two diets with the same calculated energy value do not necessarily ensure equivalent biological utilization. The outcome also depends on feed intake, digestibility, absorption kinetics, health and environmental conditions, and the bird's ability to partition substrates among maintenance, growth and storage. Therefore, in addition to quantifying the energy supplied, it is relevant to examine pathways that may enhance its metabolic availability.

Distinctive features of glucose metabolism in birds

Birds maintain plasma glucose concentrations approximately 1.5-2 times as high as those of similarly sized mammals, yet they do not normally develop the abnormalities associated with chronic hyperglycaemia in mammals (Braun and Sweazea, 2008; Sweazea, 2022). They also exhibit a distinctive response to insulin: essential components of insulin signalling are conserved, but skeletal muscle is relatively refractory.

Although avian insulin signalling differs from that of mammals, recent research has identified chicken GLUT4 and provided evidence of its function in skeletal muscle satellite cells (Zhang et al., 2024). This physiology enables high circulating glucose availability, although its regulation should not be interpreted simply as insulin resistance.

The liver plays a central role in this homeostasis. Following feed intake, it takes up and distributes absorbed nutrients, synthesizes glycogen and lipids, and regulates glucose release. Between meals, during the overnight period or when feed intake declines, glycogenolysis and gluconeogenesis help maintain blood glucose concentrations. The kidney may also contribute, particularly during prolonged fasting, but the liver remains the principal site of metabolic integration.

This regulation is particularly relevant in modern broilers. During their short production cycle, metabolic rate, body composition and the capacity for glucose oxidation change rapidly (Buyse et al., 2004). The nutritional objective is not to induce higher blood glucose concentrations, but to ensure that substrate supply and utilization keep pace with growth without unnecessarily increasing the catabolism of body reserves.

Gluconeogenesis: converting substrates to maintain homeostasis

Gluconeogenesis is the synthesis of glucose from non-carbohydrate precursors. Under physiological conditions, lactate, glycerol and glucogenic amino acids can enter the pathway at different points. Lactate is converted into pyruvate; glycerol enters through three-carbon intermediates; and the carbon skeletons of certain amino acids can generate pyruvate, oxaloacetate or other intermediates of the tricarboxylic acid cycle (Brady et al., 1979).

The pathway shares several reactions with glycolysis but must bypass its irreversible steps. Pyruvate carboxylase converts pyruvate into oxaloacetate; phosphoenolpyruvate carboxykinase generates phosphoenolpyruvate; and fructose-1,6-bisphosphatase and glucose-6-phosphatase complete glucose formation and release. Regulation of this pathway responds to nutritional status, substrate availability and the hormonal environment.

Cell-based evidence supports the biological plausibility of this strategy. In avian hepatocytes, the combination of gluconeogenic and phytogenic compounds was associated with increases in intracellular ATP, the ATP/ADP ratio and glycogen accumulation, together with greater protection against an oxidative challenge (Olivares-Ferretti et al., 2024).

Figure 1. Integration of gluconeogenic substrate supply and phytogenic functional modulation in avian energy metabolism.

What does the gluconeogenic-phytogenic strategy provide?

The combination integrates two complementary nutritional approaches targeting hepatic metabolism and efficient nutrient utilization. First, gluconeogenic substrates can enter hepatic metabolic pathways as precursors for glucose synthesis. The resulting glucose may then be released into the circulation, stored temporarily as glycogen or used by tissues for ATP production.

Second, the phytogenic fraction is specifically intended to support liver health and function. This approach is particularly relevant because the liver is the principal gluconeogenic organ in birds and plays a central role in regulating blood glucose, storing glycogen, oxidizing nutrients and synthesizing numerous metabolites. Phytogenic compounds are not a direct source of energy; rather, they may help maintain an appropriate hepatocellular environment in which these processes can proceed efficiently.

Phytogenic compounds help maintain hepatic redox balance, protect the functional integrity of hepatocytes and modulate stress-related metabolic responses. Reducing oxidative pressure is particularly relevant in fast-growing broilers, whose liver must process a high nutrient flux while sustaining intense biosynthetic activity. By preserving hepatic function, these compounds support the organ's capacity to transform, store and distribute available nutrients.

Overall, the strategy combines the supply of gluconeogenic precursors with phytogenic support directed towards the organ in which their metabolic conversion primarily occurs.

Evaluation in broilers

The trial included 1,530 one-day-old Ross AP broilers randomly allocated to 30 pens of 51 birds each. Three treatments were evaluated, with ten replicates per treatment: an unsupplemented control and a combination of gluconeogenic and phytogenic compounds supplied at 250 or 500 g/t.

The experimental period extended from 0 to 35 days and was divided into pre-starter, starter and grower-finisher phases. All diets were formulated to the same nutrient specifications and calculated metabolizable energy content; no energy reduction was applied to the supplemented treatments. Body weight, feed intake, feed conversion ratio (FCR) and European Production Efficiency Factor (EPEF) were recorded. Depending on the distribution of each variable, parametric or non-parametric analyses and multiple comparisons were performed, with differences considered significant at p ≤ 0.05.

Higher body weight with lower feed intake and improved feed conversion

At 35 days, birds in the control group reached 2,058.98 g/bird, compared with 2,107.83 g at 250 g/t and 2,137.51 g at 500 g/t. These values represent increases of 2.4% and 3.8%, respectively. Both supplemented treatments were significantly higher than the control, although they did not differ significantly from each other.

Cumulative feed intake was 2,919.7 g/bird in the control group, 2,908.7 g at 250 g/t and 2,885.8 g at 500 g/t. Birds receiving 500 g/t consumed 1.2% less feed than the control while achieving the highest body weight. The intermediate dose produced an intermediate feed intake value that did not differ significantly from either of the other treatments.

The combined effects on growth and feed intake were most clearly reflected in FCR: 1.421 in the control group, 1.383 at 250 g/t and 1.354 at 500 g/t. These values represent improvements of 2.7% and 4.7%, and all three treatments belonged to different statistical groups. EPEF increased from 405.95 to 424.75 and 440.84 points, corresponding to improvements of 4.6% and 8.6%. Significant differences among all three treatments were also observed for this parameter.

A nutritional strategy with an economic return

The performance response translated into an economic benefit despite the additional supplementation cost. Feed cost decreased from €0.546/kg body weight in the control group to €0.536 and €0.527/kg in the supplemented groups. Margin over feed cost increased from €80.91/pen to €83.57 and €85.71/pen, representing improvements of 3.3% and 5.9%, respectively. Under the conditions of the trial, greater biomass production and improved feed conversion offset the cost of supplementation.

Figure 2. Effect of the gluconeogenic-phytogenic strategy on feed cost per kilogram of body weight.

Feed cost per kilogram of body weight at 35 days of age. Percentages indicate the reduction relative to the control. The combination was supplied at 250 or 500 g/t without changing the declared nutrient or energy concentration.

Conclusions

Supplementation with the gluconeogenic-phytogenic combination resulted in a higher final body weight with similar or lower feed intake, leading to significant improvements in FCR and EPEF. The dose-dependent response observed for these parameters strengthens the consistency of the performance effect and suggests more efficient utilization of the available nutrients.

This improvement also had a favourable economic impact by reducing feed cost per kilogram of body weight produced. Overall, the results support the use of this strategy as a complement to nutritionally balanced diets.

BEYOND FORMULATED ENERGY: A GLUCONEOGENIC-PHYTOGENIC STRATEGY IN BROILERS