Factors affecting the chemical composition of milk – breed, nutrition, lactation period, and season as biological and technological determinants.

marzo 05, 2026

The chemical composition of milk is not a fixed quantity but the result of a complex interaction between genetic, physiological, and environmental factors. The breed of the animal, the type and quality of nutrition, the stage of lactation, and seasonal conditions form a dynamic framework within which the mammary gland adjusts both the quantity and structure of the main components—fat, proteins, lactose, minerals, and vitamins. This review article examines these factors as interconnected regulators of milk composition, analyzes the mechanisms of their action, and discusses their significance for quality, technological suitability, and the interpretation of analytical data.

Introduction
Classical representations of milk often rely on "average" values for its chemical composition, creating the illusion of relative constancy. In reality, milk is a biologically adaptive secretion whose composition changes in response to genetic predispositions and environmental conditions. This variability is not a defect but a functional property that allows optimal nourishment of the newborn and efficient utilization of available resources.

Understanding the factors that influence composition is crucial for both dairy science and practical applications—from herd selection and management to technological planning and quality control.

Breed as the Genetic Framework of Chemical Composition

Breed determines the genetic potential for synthesizing milk components. Different breeds are characterized by specific profiles regarding fat content, protein content, and protein fraction composition.

These differences are not limited to quantitative parameters. The genetic foundation affects the fatty acid composition of milk fat, the ratio between casein fractions, and even the mineral balance associated with the protein matrix. In this sense, the breed sets the structural style of milk—whether it will be more suitable for cheese production, butter manufacturing, or direct consumption.

From a technological perspective, breed differences have long-term significance because they determine composition stability and the predictability of technological behavior.

Nutrition as a Metabolic Regulator

Nutrition is the most powerful external factor affecting the chemical composition of milk in the short and medium term. It regulates the energy and nutrient flow to the mammary gland, directly influencing the synthesis of fats, proteins, and micro-components.

Milk fat is particularly sensitive to nutrition. Changes in energy balance and feed type lead to modifications in the fatty acid profile, affecting both nutritional value and sensory and oxidative properties. Protein composition also responds to nutrition, albeit more moderately, with changes often occurring in the ratios of protein fractions rather than in total quantity.

Nutrition also influences the vitamin and mineral profile, making milk a metabolic reflection of the animal’s diet.

Lactation Stage as a Physiological Scenario

The stage of lactation is a fundamental factor in the variability of chemical composition. Early lactation milk is usually richer in proteins and minerals, reflecting the needs of the newborn and the intense metabolic activity of the gland.

As lactation progresses, changes occur in fat and lactose content, as well as in the ratio between components. At the end of the lactation period, the relative content of dry matter often increases, which is part of a physiological adaptation mechanism.

From a systemic perspective, lactation can be seen as a temporal model of chemical composition, where each phase has a characteristic profile and technological relevance.

Season as a Complex Environmental Factor

Seasonal changes affect the chemical composition of milk through a combination of climatic conditions, feed availability, and physiological stress. Temperature fluctuations influence water balance and dry matter concentration, while seasonal changes in feed affect the lipid and vitamin profile.

For example, summer heat stress can lead to lower concentrations of certain components due to increased water intake and metabolic adaptations. Winter, on the other hand, is often characterized by more concentrated milk with a different fatty acid profile.

Seasonal variability is natural and cyclical but has important implications for long-term quality control and the interpretation of analytical data.

Interaction of Factors—A Systemic Effect

None of these factors act in isolation. Breed determines the animal's responsiveness to nutrition; nutrition modifies the expression of genetic potential; the lactation stage provides the physiological context; and season affects all other factors.

This interaction creates multilayered variability that cannot be described by a single parameter. This illustrates the systemic nature of milk composition and the need for an integrative analytical approach.

Implications for Milk Quality

Factors influencing composition directly determine milk quality. A balanced combination of genetic potential, adequate nutrition, and appropriate lactation management leads to a stable and predictable chemical profile.

Deviations in any single factor rarely result in "bad" milk on their own but may cause discrepancies between expected and actual quality, especially in a technological context.

Implications for Technological Suitability
From a technological standpoint, the factors affecting composition determine milk's suitability for various processes. Cheese production requires a specific protein-mineral balance, while butter and cream production strongly depend on fat content and profile.

Understanding these dependencies allows targeted use of raw milk, instead of a universal approach that often compromises quality.

Analytical Interpretation and Risk of Misconclusions

Without considering the factors influencing composition, analytical data may be misinterpreted. Natural variability could be mistaken for adulteration or technological failure if context is lacking.

Thus, factor analysis is a key element in the modern interpretation of milk quality.

Breed, nutrition, lactation stage, and season form the dynamic framework in which milk's chemical composition is realized. These factors do not act in isolation but in a complex interplay that determines the quantity, structure, and functionality of milk components.

Examining chemical composition without considering these factors is incomplete and potentially misleading. The review demonstrates that milk quality and technological value stem not from fixed values but from biologically justified and predictable variability. This understanding underlies the modern, scientifically grounded approach to milk as both a raw material and a food.