Residual feed intake (RFI) is an index derived from resource allocation theory used to measure the feed efficiency of growing cattle. It was first developed in 1963 by Robert M. Koch as a solution to the difficulty of determining the optimal feed for growing cattle. There are several factors that influence the RFI of cattle.
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Variation in residual feed intake
Increasing the efficiency of feedstuffs is an important goal for livestock production. A growing body of literature reports on the subject. One of the most common methods used in these studies is the residual feed intake (RFI) method. This approach quantifies between-animal variation in efficiency. It is also a useful tool for genetic evaluation and breeding schemes.
RFI estimates may be influenced by differences in the digestive efficiency of individual animals. Several factors may influence differences in animal digestion, such as differences in the way the feed is sorted. Regardless of the cause, the results point to differences in efficiency. While the NE estimations may reflect differences between animals, the difference in digestive efficiency between animals can mask a biological reality.
Most cattle in the study consumed less feed than their less efficient counterparts. They consumed about 5.03 kg less DMI per day than the least-efficient group. However, there were no significant differences in initial body weight, average daily gain, or total body weight. Moreover, there were no significant RFI x sex effects on growth performance. Moreover, the cattle from the most efficient group had higher hot carcass weight, more ribeye area, and less heart and pelvic fat compared to their less efficient counterparts.
Genetic variation in RFI
A recent study has examined genetic variation in residual feed intake (RFI) in cattle. This trait is a measure of the efficiency of a livestock diet and is important for the production of beef because it affects the cost of production, the allocation of land to alternative agriculture, and animal methane emissions. However, the study did not find significant differences in RFI among breeds.
The researchers used a series of genomic data to determine the genetic basis of RFI. Then, they identified QTLs associated with differential expression of genes that were associated with feed efficiency. Genetic differences in RFI were also associated with other traits, including average daily gain and dry matter intake. These findings may help us to develop breeding programs to improve feed efficiency by identifying genetic variants responsible for variation in cattle RFI.
The researchers also found genetic differences in the relative abundance of Eubacterium ruminantium, Fibrobacter succinogenes, and Megasphaera elsdenii in more efficient cattle than those in the inefficient group. They also found that the most efficient cattle had higher RFI than those of the inefficient group, and they also had lower total bacterial density. The findings suggest that ruminal microbes play a major role in RFI, with epithelium tissue acting as a nutrient-uptake pathway.
Effects of body composition on RFI
Biological processes and interactions between feed and body composition contribute to variations in residual feed intake (RFI) in cattle. In a study on Angus steer progeny, the differences in RFI between low and high-RFI steers were associated with differences in total energy retained in the body as fat and protein, respectively. However, this variation is small compared to differences in feed efficiency.
We assessed the effects of dietary fat on RFI in crossbred steers from five strains of BeefBooster. We found a negative correlation between RFI and subcutaneous fat depth in steers from high-efficiency and low-RFI selection lines. Further, the correlations were consistent with the regression coefficients against mid-parent EBVrfi-pw. The negative mean EBVrfi-pw was associated with greater FCR and higher growth.
We found that genetic superiority in RFI was associated with lower (better) FCR over 251 days of feeding in commercial feedlots. However, this did not appear to influence carcass weight, dressing percentage, or marbling grade.
Effects of maintenance efficiency on RFI
Several studies have evaluated the effects of maintenance efficiency on residual feed intake (RFI) in beef cattle. These studies have shown that the cattle with low RFI remain more metabolically efficient during feed restriction and adjust their maintenance requirements based on the conditions they encounter. The differences between low-RFI cattle and high-RFI cattle are evident in the animals’ behavior, performance, and heat production during restricted intake.
To test this hypothesis, the authors measured RFI in two groups. One group possessed high RFI and the other had low RFI. They also used the ADLIB method to measure ADG. They found that animals with high RFI decreased their ADG during the restricted period but not significantly. The changes in maintenance requirement were dependent on the amount of feed restricted.
Improvement in feed efficiency increases economic returns. In beef production, over 50% of the feed input is used for maintenance. This means that reducing the amount of feed used for maintenance can have a major impact on profitability and the environment.
