Summary of the article: Challenges and Methodologies to Assess Protein Requirement and Quality Across Different Life Stages in Dogs: A Review

Determining precise protein requirements in dogs remains one of the most complex challenges in companion animal nutrition. Physiological variation across life stages, the diversity of available protein sources and the limitations of classical methodologies have produced recommendations that do not always reflect the metabolic reality of the dog. Recent advances have enabled more dynamic and accurate approaches capable of assessing both the quantity of protein required and the quality of the sources used. This summary synthesises current knowledge on protein requirements and protein quality in dogs from growth through adulthood, senescence and reproduction.

Growth: high demand and real-world variability

Growth is the life stage where the complexity of establishing protein requirements is most evident. Rapid tissue deposition, organ development and elevated metabolic activity increase the demand for essential amino acids and for protein sources with high metabolic availability.

Key points

• Historical recommendations were based on highly digestible proteins, limiting applicability to commercial diets.
• Real-world formulations containing cereals and animal by-products require higher protein levels to meet amino acid needs.
• Ileal digestibility and metabolic availability are more decisive than crude protein percentage.
• The energy–protein ratio directly influences growth efficiency and nitrogen retention.
• Nitrogen balance underestimates requirements because it does not capture changes in lean mass or functional development.

Table 1. Protein ranges in growth according to formulation type

Adults: precision, efficiency and protein quality

In adulthood, protein demand decreases, yet discrepancies persist between regulatory recommendations and industrial practice. Most commercial diets exceed minimum requirements to ensure adequate essential amino acid supply.

Key points

• Lower recommendations originate from studies using crystalline amino acids with near-total availability.
• Higher recommendations reflect conventional proteins with variable digestibility.
• Industry formulations exceed minimums to secure amino acid balance rather than due to physiological need.
• High protein levels do not harm healthy adult dogs.
• Protein quality—ileal digestibility, metabolic availability, amino acid balance—is more relevant than crude protein percentage.
• Limited research on individual amino acid requirements restricts precision.

Table 2. Comparison of protein levels in adult maintenance

Senescence: increased need despite reduced intake

Geriatric dogs experience physiological changes that directly affect protein metabolism: sarcopenia, reduced appetite, lower energy expenditure, immunosenescence and cognitive alterations. These factors increase protein and amino acid requirements, although available evidence remains limited.

Key points

• Protein restriction is not justified in healthy senior dogs.
• Sarcopenia increases the need for amino acids to preserve lean mass.
• Reduced energy intake requires higher protein density in the diet.
• Some studies indicate senior dogs may need up to 50% more protein than adults.
• The role of protein in immunity, wound healing and other physiological processes in older dogs remains insufficiently characterised.

Gestation and lactation: elevated requirements and scarce evidence

The reproductive period is one of the least studied areas in canine nutrition. Most recommendations are extrapolated from growth studies, creating uncertainty in diet formulation for pregnant and lactating bitches.

Key points

• Protein requirements increase substantially due to foetal growth, mammary development and milk production.
• Excess protein should be avoided due to the risk of ammonia toxicity in embryos.
• Energy intake may increase up to 3.5-fold during lactation, allowing higher protein inclusion without compromising energy balance.
• The presence or absence of carbohydrates modifies the protein required to meet metabolic demand.
• Formulation must consider bitch size, litter size and body condition.

Male reproduction: an almost unexplored field

There is virtually no direct evidence on protein requirements for male reproductive function in dogs. Indirect insights come from other species, where maternal protein intake influences male fertility in adulthood.

Key points

• No solid data exist on protein requirements for sperm production in dogs.
• Experimental models show that maternal low-protein diets can impair male fertility in offspring.
• The mechanisms linking early-life nutrition and adult reproductive function remain unclear.

Protein quality: beyond crude protein percentage

Assessing protein quality is essential to understand the true nutritional value of an ingredient. Protein is not a homogeneous nutrient; its value depends on amino acid profile, digestibility and metabolic availability.

Key points

• Crude protein measurement does not reflect true nutritional quality.
• Ileal digestibility is more representative than total tract digestibility but is rarely measured in dogs.
• Metabolic availability determines the proportion of absorbed amino acids usable for protein synthesis.
• Modern techniques allow dynamic evaluation of protein metabolism.
• Considering protein quality in formulation improves nutritional efficiency and reduces unnecessary protein loading.

Modern methodologies: towards greater accuracy

The shift from classical methods to tracer-based techniques has advanced understanding of protein metabolism in dogs. These methodologies provide a dynamic view of protein turnover, amino acid oxidation and utilisation efficiency.

Key points

• Nitrogen balance has major limitations: it misses metabolic adaptations, underestimates non-urinary losses and requires restrictive housing.
• Isotopic tracers measure protein synthesis and degradation in real time.
• These techniques improve accuracy in determining requirements and evaluating protein quality.
• Their use enhances animal welfare by reducing restrictive experimental conditions.

Conclusion

Determining protein requirements in dogs remains an evolving field. Differences across life stages, variability in protein digestibility and the limitations of classical methodologies have produced recommendations that do not always align with physiological reality. Modern techniques enable more precise, efficient and tailored nutrition. Future progress will depend on studies integrating ileal digestibility, metabolic availability, tracer methodologies and functional assessments across life stages.