This project aimed to improve sheep producer awareness and knowledge of residual feed intake (RFI) as a measure of feed efficiency, determine relationships of RFI with other traits of economic importance and identify variants in the leptin gene associated with improved RFI. Informational packets and surveys were distributed to producers to assess and improve knowledge regarding the RFI measurement. Performance test data analyses indicated that selection for RFI in sheep should not adversely affect carcass and fleece traits. Finally, sequence data of the leptin gene did not identify any genotypic variants associated with improved RFI status.
Feed costs represent >50% of total input costs for sheep producers (Nash, 1991). For sheep producers to remain profitable, means of reducing feed usage while not sacrificing performance are necessary. Residual feed intake (RFI) is an alternative measure of feed efficiency that is independent of body weight and maturity (Koch et al., 1963), a distinct advantage over traditional measures of efficiency. It is a preferred assessment of feed efficiency in many beef cattle breeds. Genetic selection for improved RFI would allow producers to select animals that are able to perform to standard with less feed usage. However, for genetic selection of RFI to successfully improve the bottom-line for producers, RFI must not be unfavorably correlated with other economic traits of interest, including carcass merit and fleece traits. In beef cattle, carcass traits such as rib fat thickness, loin mass area and marbling score are not correlated with RFI (Ribeiro et al., 2006). There have yet to be any reports on potential implications of RFI selection on fleece traits.
The leptin hormone has a regulatory role in whole-body energy metabolism. In beef cattle, variants of the leptin gene (i.e. genotypes) have been associated with changes in performance, namely growth rate, feed intake, metabolic body weight and final slaughter weight (Lagonigro et al., 2003; Nkrumah et al., 2005; Barendse et al., 2007). It is hypothesized that a number of these variants also contribute to differences in feed efficiency observed among individual cattle and have potential to ultimately serve as markers for genetic selection. We hypothesized that some of these variants also exist in the ovine leptin gene, providing a similar avenue for marker-assisted selection to improve RFI in sheep.
- Barendse, W., A. Reverter, R. J. Bunch, B. E. Harrison, W. Barris, and M. B. Thomas. 2007. A validated whole-genome association study of efficient food conversion in cattle. Genetics. 176: 1893-1905.
Koch, R. M., L. A. Swiger, D. Chambers, and K. E. Gregory. 1963. Efficiency of feed use in beef cattle. Journal of Animal Science. 22: 486-494.
Lagonigro, R., P. Wiener, F. Pilla, J. A. Woolliams, and J. L. Williams. 2003. A new mutation in the coding region of the bovine leptin gene associated with feed intake. Anim Genet. 34: 371-374.
Nash, T. G. 1991. Getting started with sheep emphasis on a commercial operation. Illinois Sheepman’s Holiday and Symposium.
Nkrumah, J. D., C. Li, J. Yu, C. Hansen, D. H. Keisler, and S. S. Moore. 2005. Polymorphisms in the bovine leptin promoter associated with serum leptin concentration, growth, feed intake, feeding behavior, and measures of carcass merit. J Anim Sci. 83: 20-28.
Ribeiro, F. R. B., G. E. Carstens, P. A. Lancaster, L. O. Tedeschi, and M. H. M. R. Fernandes. 2006. Evaluation of feed efficiency traits in growing brahman heifers and relationship with body composition ultrasound traits and feeding behavior. In: American Society of Animal Science, Minneapolis, MN. p 123.
Objective 1. Assess and improve producer knowledge of RFI and determine acceptability of RFI adoption as the standard measure of efficiency in sheep.
Objective 2. Use producer rams on-test at the University of Wyoming to determine relationships of RFI with other traits of economic importance, including carcass and fleece traits.
Objective 3. Identify genetic markers associated with improved RFI of rams on-test for marker-assisted selection implementation in the long-term.
Human research procedures were approved by the University of Wyoming Institutional Review Board. Responses to surveys and interviews were anonymous to prevent bias, and all information provided was kept confidential. Producers (n = 14) who had previously participated in the University of Wyoming Ram Performance Test agreed to complete surveys gauging their knowledge of RFI, acceptance of incorporating RFI into current breeding programs and the use of technology such as marker-assisted selection. A 10-question survey was provided to producers prior the receiving additional information on RFI and ram RFI ranking results. Subsequently, an additional survey was completed by producers that consisted of the same 10 questions and an additional question to determine interest in selecting for RFI. The FREQ procedure in SAS was used to analyze survey responses before and after producers were provided information on RFI and ram RFI ranking results. Raw counts for operation size (<100, 101-1000 and >1000 head), type of operation (Purebred, Commercial, or both) and breeds used (Dual-purpose, meat, or both) were collected from producers for operation demographics.
All animal procedures were approved by the University of Wyoming Animal Care and Use Committee. Daily feed consumption for dual-purpose (n = 183; 7.00 ± 0.78 mo age) and meat breed (n = 147; 4.14 ± 0.33 mo age) rams were collected using the GrowSafe System during standard performance tests at the University of Wyoming. Dual-purpose rams consisted of primarily Rambouillet and Rambouillet × Targhee breeds while meat breed rams consisted of Suffolk and Hampshire breeds. Feed intake information collected by the GrowSafe System was used to determine individual RFI values. Fleece characteristics (grease fleece weight, clean fleece weight, staple length, fiber diameter, fiber grade, face score, wrinkle score and belly score) were collected on dual-purpose rams. Ultrasound was used to determine carcass (backfat and loin eye area) traits on all rams. Relationships were determined between RFI and carcass characteristics and fleece measurements using the CORR procedure (Pearson method) of SAS.
Six contemporary groups of dual-purpose (n = 100) and meat breed (n = 220) rams from the annual University of Wyoming performance tests were used for DNA analysis. Residual feed intake measurements were available for all rams. Blood was collected from each ram and DNA extracted from white blood cells for sequencing and detection of genotypic variants. Breeds analyzed in the current study included Rambouillet, Colombia, Targhee, Suffolk and Hampshire. Primers were designed for leptin and its promoter to span introns using bovine sequences. Sequencing was performed in collaboration with USDA MARC (Clay Center, NE). DNA was genotyped using primer extension on the Sequenom MassArray system (San Diego, CA).
Approximately 28% of surveyed sheep producers had >100 head of sheep, 56% had 101-1000 head of sheep, and 16% had >1000 head of sheep in their operation. The sheep operations surveyed were composed of 68% purebred, 16% commercial and 16% a combination of operational types. The majority of ranchers surveyed produced dual-purpose breeds (56%) with the remaining 36% and 8% composed of meat breeds or both, respectively. Initially, 57% of surveyed producers agreed that they had a selection program for feed efficiency, but in the final survey only 36% agreed, perhaps based on their initial interpretation of feed efficiency itself. Initially, 36% of producers agreed and 36% were neutral regarding selection of sires based on EPD information initially; however, the producers agreeing increased to 64% in the final survey. In both initial and final surveys, 36% of producers agreed that they were knowledgeable about RFI. Initially, 86% of producers were interested in receiving more information about RFI; this figure rose to 91% in the final survey. Producers agreed (64%) or strongly agreed (36%) that traits that unfavorably affected reproduction should be avoided. This was confirmed in the final survey. In both initial and final surveys, producers agreed that carcass merit traits are important. Producers strongly agreed in both the initial (57%) and final (45%) surveys that selection for wool traits is important. Producers generally agreed (45%) or were neutral (27%) on previous use of genetic markers in the initial survey; however, 30% agreed and 30% were neutral in the final survey. If available, at least 50% of sheep producers would use genetic markers to select for feed efficiency. Initially, 64% of producers agreed they would like additional information on genetic markers, but interest in genetic marker information decreased by 9% in the final survey. Overall, there were no differences (P ? 0.133) survey answers before or after producers were provided with information on RFI and the performance of their rams. In the final survey, 100% of producers agreed or strongly agreed that they would select for RFI if such information were available. These results reflect data from the Red Angus Association of America that indicated that >40% of commercial and seedstock producers were willing to adopt RFI as an alternative measure of feed efficiency. We confirmed that reproduction and fleece traits are important to producers and should be considered in genetic selection decisions. Additionally, producer interest in the RFI measurement and incorporation into breeding decisions was high.
There was no relationship (P ? 0.152) between RFI and backfat or loin eye area in either dual-purpose or meat breed ram groups. This is in agreement with beef cattle data that also reported no relationship between RFI and backfat (Moore et al., 2009). Additionally, limited reports in swine also indicate no relationship between RFI and loin eye area. There were no relationships (P ? 0.121) between RFI and grease fleece weight, clean fleece weight, staple length, face score or wrinkle score. Residual feed intake had an inconsistent relationship with belly score dependent upon the contemporary group; however, the relationship appeared to be limited overall. These results indicate that selection for RFI will not adversely affect carcass or fleece traits in sheep.
Partial sequences for leptin and its promoter were aligned to the ovine genome using http://www.livestockgenomics.csiro.au/cgi-bin/gbrowse/oar1.0/. Sequence alignment to the bovine genome was obtained using UMD_3.1 whole shotgun sequence and Btau_4.6.1 scaffold64 in NCBI and UMD_3.1 bosTau6 and Baylor 4.0/bosTau4 assemblies within the UCSC Blat search. Four of the five bovine amplicons for leptin aligned to regions within the ovine genome at approximately 98.1 Mb on chromosome 4. Sequence alignment was most similar to amplicons for leptin using the NCBI UMD_3.1 bovine assembly. Only the anterior and posterior regions of the leptin promoter could be sequenced. The middle region was heavily composed of GCs and base repeats. Therefore, only segmental regions (n = 2) were sequenced for the promoter region for SNP detection. One region within the promoter region partially aligned to approximately 98.1 Mb on chromosome 4 for the ovine genome and aligned to chromosome 4 within the bovine genome. Two promoter regions did not align to any region within either ovine or bovine genomes, and one promoter region aligned to chromosome 11 (zinc finger region of BTB containing protein 43) on both the UMD_3.1 and Btau_4.6.1 scaffold 64 assemblies. No SNPs were identified within leptin or its promoter region. However, because only segmental regions of the promoter could be sequenced, polymorphisms within the promoter region associated with RFI may be present but could not be determined in this study. Our results indicate that the variants in the leptin gene associated with feed efficiency in beef cattle are not paralleled in sheep. However, it is possible that variants in the leptin promoter may exist and be associated with RFI; the ability to fully sequence the promoter regions is necessary before this can be tested. Furthermore, a whole-genome approach may be better suited to finding genotypes associated with variation in RFI in sheep.
Moore, S. S., F. D. Mujibi, and E. L. Sherman. 2009. Molecular basis for residual feed intake in beef cattle. J Anim Sci. 87: E41-47.
Educational & Outreach Activities
- Publications (**Ph.D. student advised by PI)
**Cockrum, R. R., L. A. Rempel, S. Berry, R. H. Stobart, S. L. Lake, K. M. Cammack. Leptin and its promoter sequence and polymorphisms within the sheep genome. Animal Genetics (In-progress).
**Cockrum, R. R., R. H. Stobart, S. L. Lake, K. M. Cammack. Phenotypic variation in residual feed intake and performance traits in rams. Small Ruminant Research (In-review).
**Cockrum, R. R., S. L. Lake, R. H. Stobart, K. M. Cammack. 2013. Ovine genomic sequence and polymorphisms present in leptin and promoter region. Pg. 202. Plant and Animal Genome XXI Conference, San Diego, CA.
**Cockrum, R. R., R. H. Stobart, S. L. Lake, K. M. Cammack. 2011. Evaluation of feed efficiency in Rams using the GrowSafe System. University of Wyoming Department of Animal Science Annual Report.
**Cockrum, R. R., as written by staff writer S. Albert. GrowSafe research project first of its kind. 2011. Wyoming Round-Up.
Presentations (**Ph.D. student advised by PI)
**Cockrum, R. R. “Evaluation of residual feed intake in rams using the GrowSafe system” Wyoming Rambouillet Association. 2011
**Cockrum, R. R. “Effects of residual feed intake selection in sheep” Wyoming Rambouillet Association. 2010.
**Cockrum, R. R. “Incorporating feed efficiency with selection programs in sheep” American Sheep Cockrum, R. R. Industry/National Lamb Feeders Association. 2012. Annual Convention, Scottsdale, AZ.
Cammack, K. M. “Residual feed intake applications in sheep” AgResearch, Mosgiel, New Zealand. 2011.
Encouragingly, survey results indicated that producers were interested in implementing new genetic selection strategies, especially those that included feed efficiency measures such as RFI. Our results showing limited relationships between RFI and other traits of economic importance, including both carcass and fleece traits, will be especially helpful when demonstrating the use of RFI in breeding decisions to producers. Alleviating such concerns is critical step in the adoption of new genetic selection strategies. Because of the positive feedback and high interest in the RFI measurement, it will continue to be evaluated in future ram tests at the University of Wyoming.
While the interest in RFI is encouraging, we still realize that measurement of this trait is expensive and both labor and time-intensive. Therefore, identifying alternative means of selecting for RFI (other than direct measurement) will be critical in advancing this trait in genetic selection programs. Use of marker-assisted selection strategies would be ideal in this situation. Our approach in this study was to look for genotypic variants in a gene known to be involved in the feed intake regulatory system – leptin. Previous beef cattle data had demonstrated variants in the leptin gene and its promoter were associated with variation in feed efficiency. Our study did not reveal any variants in the leptin gene that were associated with RFI in sheep. However, we were unable to successfully sequence the leptin promoter, so it is possible that variants may be present in that sequence. A whole-genome approach may be better suited to finding genotypes associated with variation in RFI in sheep.
Economic information collected from producers (using surveys approved by the UW Institutional Review Board) indicated that producers are not currently realizing any premiums from using RFI information. Low RFI rams did not achieve slaughter weight earlier than high RFI rams. However, future economic analysis will focus on reductions in input cost to maintain low RFI rams compared to high RFI over a similar feeding period.
Surveys presented to area sheep producers have indicated their interest in incorporating RFI into current breeding strategies. Because of the high interest in RFI, this trait will continue to be part of the University of Wyoming ram tests. Producers recognize the value of feed efficiency measures and are generally open to practicing marker-assisted selection when such tools become available. This project was successful in introducing and improving knowledge of the RFI concept and its use in their operations.
Areas needing additional study
The mechanisms involved in regulating and controlling feed efficiency are still unknown. There is much hype surrounding the idea that rumen microbial populations play a significant role in the efficiency of feed utilization. Research is needed to determine the role of the rumen microbiome on the host feed efficiency. Additionally, whole-genome approaches may help identify polymorphisms associated with the variation in feed efficiency in sheep. Identification of such polymorphisms, followed by deep sequencing to identify genes/gene segments, is needed to identify genetic markers for producer/industry use.