- The genetics of feed efficiency examines how inherited genetic differences influence an animal’s ability to convert feed into growth, milk, meat, eggs, or other useful products. Feed efficiency is an economically important trait in livestock production because feed represents a substantial proportion of production costs. Improving feed efficiency through genetic selection can reduce feed requirements per unit of output, improve profitability, and support more sustainable animal production while maintaining animal health and welfare.
- Feed efficiency is influenced by many genes that affect appetite, digestion, nutrient absorption, metabolism, maintenance requirements, body composition, and the allocation of nutrients to growth or production. These genetic factors interact with nutrition, feed quality, housing, climate, health, and management. Consequently, differences in feed efficiency between animals reflect both genetic and environmental influences. Quantitative genetics provides methods for separating these sources of variation and estimating the genetic potential of animals for efficient feed utilization.
- Several measurements are used to evaluate feed efficiency. Feed conversion ratio (FCR) expresses the amount of feed consumed per unit of output, such as body weight gain; a lower FCR generally indicates better efficiency when animals are compared under equivalent conditions. Feed efficiency ratio expresses output relative to feed intake, so a higher value generally indicates better efficiency. Other measures include residual feed intake, feed intake per unit of milk produced, and feed required to produce a kilogram of eggs or meat. The appropriate measure depends on the species, production system, and breeding objective.
- Residual feed intake (RFI) is an important measure in animal breeding. It represents the difference between an animal’s actual feed intake and its expected feed intake based on factors such as body size, growth rate, and production. Animals with lower RFI consume less feed than expected for their level of performance and are often considered more feed-efficient. Because RFI accounts for specified production and maintenance requirements, it can help identify animals that use feed more efficiently without simply selecting those that grow more slowly or produce less. Its interpretation nevertheless depends on the statistical model and traits included in the calculation.
- Genetic variation in feed efficiency allows breeders to improve this trait through selection. Heritability estimates the proportion of phenotypic variation attributable to genetic differences within a particular population and environment. Feed-efficiency traits often have low to moderate or moderate heritability, depending on the species, population, measurement method, and trait definition. Accurate feed-intake recording can be expensive, however, so reliable genetic evaluation depends on suitable measurement systems, well-designed trials, and sufficient numbers of animals with both performance and pedigree or genomic information.
- Breeding values help estimate an animal’s inherited genetic merit for feed efficiency. Genetic evaluations can combine feed intake, growth, body weight, production records, pedigree information, and performance data from relatives. Breeding animals with favourable estimated breeding values can gradually improve efficiency in subsequent generations. Because feed efficiency can differ across diets, ages, and production systems, breeders should ensure that genetic evaluations represent the environments in which the offspring are expected to perform.
- Modern breeding programs increasingly use genomic selection to predict feed-efficiency potential from DNA marker information. Genomic predictions can help identify promising young animals before extensive feed-intake records are available. Their accuracy depends on the quality of the reference population, the amount of reliable phenotypic data, the genetic relationships between animals, and the genetic architecture of the trait. Genomic selection is particularly useful when direct measurement is costly or difficult, but it requires continuing validation and updated records to maintain reliable predictions.
- Feed efficiency is genetically related to growth rate, mature body size, body composition, fertility, health, and longevity. Selecting for greater efficiency may reduce feed costs, but the consequences depend on how the trait is defined and which biological mechanisms contribute to improvement. For example, selecting for low RFI may improve efficiency while maintaining growth and production, whereas selecting only for a lower feed conversion ratio may favour faster growth and could increase mature size or maintenance requirements. Genetic correlations and selection indexes help breeders balance feed efficiency with production, reproduction, robustness, and animal welfare.
- Improving feed efficiency may also reduce the amount of feed required per unit of product and can lower emissions associated with feed production and digestion per unit of output. However, the environmental benefit depends on factors such as diet composition, manure management, production level, and the species involved. Efficient animals must still receive adequate nutrition, and breeding objectives should not compromise health, fertility, or normal behaviour in pursuit of lower feed intake.
- Sustainable genetic improvement of feed efficiency requires accurate recording, suitable genetic evaluation, balanced selection objectives, and long-term monitoring of animal performance. Combining feed-intake data, growth and production records, breeding values, and genomic information can help identify animals that produce efficiently under relevant conditions.
