The global population is increasing and parallel to it the demand for food is increasing. The amount of land available to produce more food, however, is not. Resultantly, there is an increasing urgency to develop strategies for improved efficiency of food production. For the beef cattle producer, improved nutrient utilization (feed efficiency) by their cattle can translate to improved veld and resource use efficiency, lower finishing feed costs and greater profitability.
There have been various contributions to the science of animal nutrition that have led to positive developments in feed formulation, supplementation and processing (Brito et al., 2020). Despite the effectiveness of these advancements, it is recognised that there is a need for more permanent improvements to feed efficiency which could be achieved via genomic selection of livestock. Identifying animals for selection could be challenging as there is a lot of variation observed for feed efficiency due to the environment and composition of the feed playing such large roles in the expression of feed efficiency. However, individuals targeted for selection would be those that consume less without compromising on performance or those that produce more/perform better in comparison to the rest when consuming the same quantity of feed (Brito et al., 2020).
Feed efficiency as a trait is difficult to measure, therefore it is commonly measured through indicator traits such as, Average daily feed intake (AFI; kg/day), Residual feed intake (RFI; kg/day), Average daily gain (ADG; kg/day), Net feed intake post-weaning (NFI-P; kg/day) and Net feed intake feedlot finishing (NFI-F; kg/day) (Rolf et al., 2011).
Gross feed efficiency has been reported to have a strong, positive phenotypic correlation with growth, meaning that selecting for it can lead to larger mature size and increased maintenance requirements (Rolf et al., 2011). This correlation was exploited in past years; however, producers have become increasingly aware in recent years that large mature size does not necessarily translate to increased profitability. Contrastingly, it more so means increased maintenance requirements.
To combat the difficulty and cost of accurate performance measurement and the challenge of undesirable phenotypic correlations, several studies have investigated the bovine genome in search of single nucleotide polymorphisms (SNPs) or quantitative trait loci (QTL) within the genome that may be associated with feed efficiency indicator trait variation. Table 1 summarizes a few such studies.
| Table 1. A summary of various studies investigating genomic associations with feed efficiency traits through genomic technologies. | ||||
| Country and Breed | Aim | Results | Conclusion | Reference |
| USA, Angus | To conduct a genome-wide association study (GWAS) exploring the genome for areas associated with average daily feed intake (AFI), residual feed intake (RFI) and average daily gain (ADG), to evaluate if consistency between genomic regions for feed efficiency traits would make selection decisions and marker-assisted selection for small panels more difficult. | The study identified various significant SNPs associated with AFI, RFI and ADG variation and validated them through previous independent studies. The SNPs explained a moderate proportion of genomic BLUP (GBLUP) variance for the breeding values of the traits (AFI, 24.10%; RFI, 29.85%; ADG, 26.54%). Further, genomic regions were identified that harboured specific QTL associated only with growth efficiency and not with growth. The detection of these QTL indicates a possibility to select for improved feed efficiency without including a correlated response in mature size. | Incorporating molecular breeding values for feed efficiency indicator traits into selection indexes could allow for appropriate selection to increase profitability without creating opportunity for undesirable correlated responses in mature size. | Rolf et al., 2011 |
| Canada, Crossbreed cattle | To identify SNPs for residual feed intake, to estimate the amount of variation in RFI explained by the identified SNPs, to investigate the influence of the detected SNPs on carcass traits to avoid any undesirable correlations when selecting for feed efficiency and to map candidate genes associated with the identified SNPs to biological pathways and mechanisms. | SNPs significantly associated with residual feed intake were found on various chromosomes throughout the bovine genome. 98 significant SNPs explained 26% of the genetic variance for RFI and the candidate genes associated with those significant SNPs were involved in 35 biological processes and 39 biological pathways, all linked to feed efficiency traits. | The identification of several SNPs that are significantly associated with feed efficiency and carcass traits led to the postulation that the identified SNPs along with their candidate genes and biological mechanisms, could possibly be responsible for the variations observed in feed efficiency and carcass traits. The merit of this postulation should be measured in other populations for further validation. | Abo-Ismail et al., 2014 |
| Brazil, Nellore | To investigate genomic regions associated with feed efficiency indicator traits in zebu cattle. | Low heritability of 0.13 was estimated for feed efficiency. However, moderate to high heritabilities were estimated for feed efficiency indicator traits residual feed intake, average daily gain and dry matter intake and (0.18, 0.43, 0.47, respectively). 9 candidate genes were reported to be associated with the feed efficiency traits. | Having identified genomic regions and candidate genes allows for contributions to a genetic basis for feed efficiency in Nellore cattle, as well as other potential zebu cattle breeds. | Olivieri et al., 2016 |
| Canada, Charolais; Angus; Kinsella composite hybrid | To investigate the beef cattle genome in search of SNPs that contribute to variation in microbial composition within the rumen, influencing the feed efficiency of individual hosts. | Moderate heritability of 0.15 calculated for various rumen microbial features. Furthermore, 14 out of 19 identified SNPs were reported to be associated with rumen microorganism species, and 5 of those SNPs are strongly associated with bovine feed efficiency. | The results suggest heritability of rumen microbial features and influence of host genetics on them. This indicates potential for selecting and breeding for improved efficiency of the rumen microbiota and further improvement of bovine feed efficiency. | Li et al., 2019 |
Heritability estimates for feed efficiency indicator traits were estimated in the studies summarized in Table 1 to fall within the moderate to high range of 0.19-0.42 (Abo-Ismail et al., 2014; Olivieri et al., 2016). This range of heritability estimates indicate that effective selection for feed efficiency indicator traits based on estimated breeding values is feasible, provided that the traits are measured sufficiently. In addition to this, the results from these studies were promising. With the use of various genomic technologies (GWAS; GBLUP; genomic estimated breeding values, GEBVs) several regions in the bovine genome were detected that have been reported to be associated with feed efficiency indicator traits, some distinctively apart from regions associated with growth. This would allow for the avoidance of undesirable correlation responses in mature size when including feed efficiency indicator traits in selection indexes (Rolf et al., 2011). Furthermore, several significant SNPs that explained notable portions of variation for feed efficiency indicator traits were also detected. An example of what these study results look like when applied in practice can be seen in Fig. 1.
Fig. 1 illustrates the effectiveness of selecting for feed efficiency. West Virginia University Davis College, in collaboration with Vytelle (“an integrated technology platform built to accelerate genetic progress in cattle”), demonstrated feed efficiency by placing the bags of feed consumed by two genetically related bulls over a 77-day feed efficiency trial, parallel to one another (LinkedIn: Vytelle, 2023; Vytelle, 2023). The result is the difference in feed intake between an efficient and an inefficient animal, where both gained the same quantity of weight.
Fig. 1 Visual representation of the results of selection for feed efficiency by Vytelle and West Virginia University (LinkedIn: Vytelle, 2023). 1lb = 0.454kg.
In conclusion, as the global population increases, there is an ever-growing need for improved production efficiency to meet the increasing demand. Whilst there are many environmental factors that can influence feed efficiency variation in cattle, various studies have detected genomic regions that have been associated with feed efficiency indicator trait variation. Along with moderate to high heritability estimates, this indicates that genetic progress can and have been made for feed efficiency indicator traits in cattle.
References
Abo-Ismail, M.K., Vander Voort, G., Squires, J.J., Swanson, K.C., Mandell, I.B., Liao, X., Stothard, P., Moore, S., Plastow, G. and Miller, S.P., 2014. Single nucleotide polymorphisms for feed efficiency and performance in crossbred beef cattle. BMC genet. 15(1), 1-14.
Brito, L.F., Oliveira, H.R., Houlahan, K., Fonseca, P.A., Lam, S., Butty, A.M., Seymour, D.J., Vargas, G., Chud, T.C., Silva, F.F. and Baes, C.F., 2020. Genetic mechanisms underlying feed utilization and implementation of genomic selection for improved feed efficiency in dairy cattle. Canadian J. Anim. Sci. 100(4), 587-604.
Li, F., Li, C., Chen, Y., Liu, J., Zhang, C., Irving, B., Fitzsimmons, C., Plastow, G. and Guan, L.L., 2019. Host genetics influence the rumen microbiota and heritable rumen microbial features associate with feed efficiency in cattle. Microbiome. 7, 1-17.
LinkedIn: Vytelle, 2023. August marks 20 years of a partnership with WVU Davis College of Agriculture, Natural Resources and Design at Reymann Memorial Farms West Virginia University. LinkedIn. https://www.linkedin.com/posts/vytelle_august-marks-20-years-of-a-partnership-with-activity-7101198768556933120-qLjr?utm_source=share&utm_medium=member_desktop.
Olivieri, B.F., Mercadante, M.E.Z., Cyrillo, J.N.D.S.G., Branco, R.H., Bonilha, S.F.M., de Albuquerque, L.G., Silva, R.M.D.O. and Baldi, F., 2016. Genomic regions associated with feed efficiency indicator traits in an experimental Nellore cattle population. PLoS One. 11(10), p.e0164390.
Rolf, M.M., Taylor, J.F., Schnabel, R.D., McKay, S.D., McClure, M.C., Northcutt, S.L., Kerley, M.S. and Weaber, R.L., 2012. Genome‐wide association analysis for feed efficiency in Angus cattle. Anim. Genet. 43(4), 367-374.
Vytelle, 2023. https://vytelle.com/.