Date: 28/07/2026

Feed conversion ratio is one of the primary indicators used to evaluate efficiency and production costs in animal agriculture. Therefore, diet evaluation must consider more than nutritional composition alone. Actual feed intake, nutrient availability and digestibility, ingredient quality, and animal performance all directly influence production outcomes.

This indicator shows how much feed is required to generate productive gain, combining the effects of nutrition, management, and production conditions into a single metric. Based on this relationship, it is possible to determine whether variations in performance are associated with diet formulation, nutrient digestibility, ingredient selection, animal health, environmental conditions, or feeding management practices.

In this article, you will learn:

What is feed conversion ratio, and why is it important?

Feed conversion ratio is the indicator that relates the amount of feed consumed to the weight gain achieved over a given period. The calculation varies according to species, production stage, and production system, but follows the same principle: dividing feed, diet, or dry matter intake by the amount of weight produced.

The Food and Agriculture Organization of the United Nations (FAO/UN) uses the concept of Feed Conversion Ratio to express the relationship between feed supplied and body weight produced. In the scientific literature, Feed Conversion Ratio is the standard metric used to indicate the amount of feed required to produce 1 kg of body weight gain, biomass, or animal product.

Therefore, feed conversion ratio should be interpreted as a production efficiency indicator alongside variables such as actual feed intake, average daily gain, diet cost, ingredient digestibility, palatability, animal health, and management practices. Although the index summarizes the relationship between feed consumption and performance, it only supports sound technical decisions when evaluated within the production context.

Which factors influence feed conversion ratio

Feed conversion ratio results from the interaction between diet, the animal, and the production environment. Therefore, changes in feed conversion ratio do not necessarily indicate a nutritional problem alone. Several factors must be evaluated to understand their impact on animal weight gain.

Ingredient quality and nutrient digestibility

Ingredient quality influences feed intake, palatability, and nutrient utilization. Ingredients with the same crude protein content may produce different responses due to differences in digestibility, amino acid profile, processing, or stability. When evaluating feed conversion ratio, it is not enough to consider how much the animal consumes. It is equally important to determine whether the feed is digested, absorbed, and converted into body weight gain, biomass, or animal products. In many cases, these outcomes are determined by ingredient quality.

A study evaluating the use of poultry protein hydrolysates in diets for Nile tilapia fingerlings​​ demonstrates this relationship. The research was conducted at the Aquaculture Laboratory of the Fisheries Engineering Program at the State University of Western Paraná (Unioeste). A total of 420 Nile tilapia fingerlings, with an average body weight of 1.8 ± 0.7 g, were assigned to seven dietary treatments with four replicates over a 30-day period. Experimental diets contained between 0% and 6% chicken protein hydrolysate.

The study identified a quadratic response for apparent feed conversion ratio, with the optimal inclusion level occurring at approximately 3% hydrolysate. In other words, performance improved up to a certain inclusion rate but did not increase proportionally at higher levels. According to the study’s conclusions, both the type of ingredient and its inclusion level influence productive performance, without a linear relationship between dosage and results.

Genetics and production stage

Genetics determines part of the animal’s growth potential, voluntary feed intake, tissue deposition, and nutrient utilization efficiency. Production stage also influences performance because growing, finishing, breeding, and young animals have different requirements for energy, protein, amino acids, and minerals. Consequently, the same diet may result in different feed conversion ratios depending on the animals’ age, body weight, sex, and production profile.

A study on the characterization and influence of production factors in grow-finish pig farms illustrates the impact of genetics on feed conversion. The analysis included records from 216 farms, 1,533 production batches, and approximately 1.025 million pigs. Among the 30 production factors evaluated, the final model identified animal origin, sex, initial weight, final weight, number of pigs per pen, and feeder design as significant variables affecting average daily feed intake and feed conversion ratio. Together, these factors explained approximately 55% of the total variation observed in feed conversion.

Animal health

Animal health directly affects feed conversion ratio because infectious, inflammatory, respiratory, and enteric challenges alter feed intake, metabolism, and growth. Under these conditions, nutrients are diverted from body weight gain toward immune response, maintenance, and tissue repair. The result is reflected in both reduced feed intake and poorer utilization of consumed nutrients.

The meta-analysis of feed intake and growth responses of growing pigs after a sanitary challenge compiled data from 122 experiments involving growing pigs exposed to six types of health challenges: enteric bacterial infections, poor housing conditions, lipopolysaccharide challenge, mycotoxicosis, parasitic infections, and respiratory diseases. All challenges reduced average daily feed intake and average daily gain. The greatest effects were observed in mycotoxicosis, respiratory diseases, and enteric bacterial infections, with feed intake decreasing by 8% to 23% and weight gain by 16% to 29%.

Feeding management

Feeding management determines how the formulated diet is delivered to the animal. Key factors affecting actual feed intake include:

  • ● Feeder adjustment;
  • ● Feeding frequency;
  • ● Water availability;
  • ● Stocking density;
  • ● Particle size;
  • ● Feed physical form;
  • ● Mixing uniformity; and
  • ● Daily operational practices.

Feed wastage, competition at the feeder, or inconsistent feed delivery can worsen feed conversion ratio even when the diet formulation is appropriate.

The technical bulletin Feed delivery systems for growing-finishing pigs and productivity indices, published by Embrapa Swine and Poultry, reports that the growing and finishing phases can account for up to 80% of total production costs, with feed representing the largest expense. The publication also identifies feed conversion ratio in swine production as being influenced by factors such as:

  • ● Genetics;
  • ● Sex;
  • ● Flooring type;
  • ● Stocking density;
  • ● Nutrition;
  • ● Animal health;
  • ● Daily management;
  • ● Environmental conditions;
  • ● Ingredient particle size;
  • ● Feed physical form;
  • ● Feeder space;
  • ● Equipment adjustment;
  • ● Feeding frequency; and
  • ● Feed delivery.

Environmental conditions

Environmental conditions also affect feed intake, energy expenditure, and metabolic response. Temperature, humidity, ventilation, stocking density, water quality, and thermal comfort can influence both feed consumption and the efficiency of tissue deposition. Under heat stress, for example, part of the energy consumed is redirected to thermoregulation mechanisms, reducing the amount available for growth.

The meta-analysis Effect of constant and cyclic heat stress on growth performance, water intake, and physiological responses in pigs compiled data from 7,230 pigs across 112 published studies. Under cyclic heat stress, average daily feed intake decreased by 15.1% and average daily gain by 15.2%. Under constant heat stress, feed intake declined by 23.2% and weight gain by 25.3%. The study also reported a 60% increase in water intake and reduced feed efficiency.

Therefore, feed conversion ratio should be evaluated as the outcome of an integrated production system. Ingredient quality, digestibility, genetics, animal health, management, and environmental conditions all interact. When any of these factors is out of balance, feed conversion ratio may worsen even if the diet itself is nutritionally well formulated.

How does nutrition affect animal production efficiency?

Nutrition affects animal production efficiency because it determines how consumed feed is converted into productive performance while supporting physiological functions. To achieve this, diets must meet the nutritional requirements of each species and production stage without excesses, deficiencies, or nutrient imbalances. Four factors play a key role in production efficiency:

  • ● Proper diet formulation: takes into account animal category, body weight, growth stage, production objectives, environmental conditions, ingredient costs, and expected field performance. Diets should be formulated based on available nutrients rather than solely on crude nutrient values.
  • ● Nutritional balance: involves the proper relationship among energy, digestible protein, amino acids, minerals, vitamins, and feed additives. When an essential nutrient falls below the animal’s requirements, productive performance may be limited.
  • ● Nutrient availability: depends on ingredient digestibility and on how efficiently protein, energy, and amino acids are absorbed and utilized. Ingredients with greater metabolic availability promote more efficient nutrient utilization.
  • ● Ingredient utilization: requires quality control, raw material consistency, palatability, proper processing, and compatibility among dietary components. Ingredients with poor acceptance or lower digestibility can compromise animal performance.

Therefore, ingredient selection and diet formulation should consider not only nutritional composition but also digestibility, nutrient availability, and the expected performance within the production system.

What is the role of digestibility in feed conversion ratio?

Digestibility directly influences feed conversion ratio because it determines the proportion of ingested nutrients that is effectively absorbed and utilized by the animal. In animal nutrition, formulating diets based solely on crude protein, energy, or mineral content is not enough. Productive performance depends on the bioavailability of these nutrients.

For protein, the focus should be amino acid utilization. When a protein source has high digestibility, more amino acids become available for growth, maintenance, immune function, and muscle development. Conversely, lower digestibility reduces the proportion of dietary protein converted into productive performance and may increase nutrient losses.

Hydrolyzed proteins address this challenge because they undergo enzymatic hydrolysis, a process that breaks protein chains into peptides and free amino acids, improving their nutritional utilization. This characteristic increases the bioavailability of nitrogen-containing compounds in the digestive tract, making protein utilization more efficient, particularly during periods of high nutritional demand, dietary transition, or digestive system development.

When formulating diets, these ingredients should be evaluated not only for their protein content but also for their digestibility, palatability, and expected contribution to productive performance. The greater the nutrient utilization, the lower the potential feed losses and the more consistent the relationship between feed intake and productive gain.

How can ingredient selection improve feed conversion ratio?

Ingredient selection directly influences feed conversion ratio because it determines the nutritional, sensory, and functional quality of the diet. For nutritionists and feed formulators, decisions should not be based solely on cost per ton or crude protein and energy levels. The most important criterion is how effectively each ingredient contributes to feed intake, digestibility, formulation stability, and productive performance.

In practice, the following criteria can help identify ingredients with greater potential to improve production efficiency:

  • ● Evaluate raw material quality. Consider nutritional composition, origin, processing, stability, and amino acid profile. Highly variable raw materials require tighter formulation control.
  • ● Maintain consistency between batches. A consistent nutritional composition helps support feed intake, weight gain, and uniform performance throughout the production cycle.
  • ● Consider palatability as a technical criterion. Aroma, flavor, and physical form influence feed intake, particularly during stages when animals are more sensitive.
  • ● Prioritize digestibility, not just crude composition. Ingredients with higher digestibility improve nutrient utilization and promote more consistent feed conversion results.
  • ● Evaluate nutritional reliability. Choose ingredients with consistent quality, standardized composition, and stable characteristics to maintain dietary balance and reduce risks to animal performance.

Feed conversion ratio: production efficiency starts with nutrition

Feed conversion ratio is a strategic performance indicator because it reflects the relationship between feed consumption and productive output. When evaluated alongside feed intake, weight gain, diet cost, animal health, and management practices, it supports decisions related to diet formulation, ingredient selection, and production system optimization.

Accordingly, changes in feed conversion ratio should be investigated from a whole-system perspective rather than by examining feed formulation alone. Imbalances in feed intake, animal health, environmental conditions, or feed delivery can impair feed conversion even when the diet is nutritionally adequate.

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Frequently asked questions about feed conversion ratio

What is feed conversion ratio?

Feed conversion ratio is the indicator that relates feed consumption to the amount of body weight, biomass, or animal product generated over a given period. It shows how much feed is required to produce 1 kg of productive output.

How is feed conversion ratio calculated?

Feed conversion ratio is calculated by dividing feed intake by weight gain during the evaluation period:

Feed conversion ratio = feed intake ÷ weight gain

What factors influence feed conversion ratio?

Feed conversion ratio is influenced by ingredient quality, nutrient digestibility, nutritional balance, genetics, production stage, animal health, environmental conditions, water availability, diet palatability, feeding frequency, and feed wastage.

How can nutrition improve production efficiency?

Production efficiency can be improved through diets formulated according to the nutritional requirements of each species and production stage, with the proper balance of energy, digestible protein, amino acids, minerals, and vitamins, while using high-quality, highly digestible ingredients.

What is the relationship between digestibility and feed conversion ratio?

Digestibility determines how much of the nutrients consumed are absorbed and utilized by the animal. The more efficiently nutrients are utilized, the better the feed conversion ratio.

How do ingredients affect feed conversion ratio?

Ingredients affect feed conversion ratio because they determine the nutritional quality, palatability, digestibility, and safety of the diet. Ingredients with high nutrient availability and consistent composition promote better nutrient utilization and more predictable production performance.