Residual Feed Intake - Producer Adoption and Genetic Selection Potential

View the project final report

• 2011 annual report

Commodities

• Animals: sheep

Practices

• Animal Production: livestock breeding
• Education and Training: extension

Feed costs represent approximately 50-70% of total input costs for sheep producers. 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, a distinct advantage over traditional measures of efficiency. 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 reproductive capability and carcass merit. The leptin hormone has a regulatory role in whole-body energy metabolism. In beef cattle, variants of the leptin gene and its promoter (i.e. genotypes) have been associated with changes in performance, namely growth rate, feed intake, metabolic body weight, and final slaughter weight. Because many of these traits are directly related to efficiency, it is hypothesized that a number of these variants also contribute to differences in feed efficiency observed among individual animals, and will ultimately serve as markers for genetic selection.

The objectives of this Western SARE Professional + Producer grant are to 1) assess and improve producer knowledge of RFI and determine the acceptability of RFI adoption as the standard measure of efficiency in sheep, 2) use producer rams on-test (from two ram tests) at the University of Wyoming (UW) to determine relationships of RFI with other traits of economic importance, including reproductive performance (as assessed by subsequent breeding records submitted by producers) and carcass merit (as assessed by ultrasound measurements of backfat (BF) and loineye area (LEA) of rams collected at beginning and conclusion of test period), and 3) identify genetic variants within the leptin gene (i.e. genotypes) associated with improved RFI as potential markers for marker-assisted selection in the long-term.

Eight producers that regularly submit rams to the UW Ram Test have been recruited as partners in this endeavor. Producers have agreed to allow the PI to access performance data generated during the test periods (including RFI data), use ultrasound to measure BF and LEA, and collect blood samples from rams for genotype analysis. Producers will complete an initial survey indicating their current knowledge of RFI and their interest in using genetic markers to improve flock efficiency. After completion of Objectives 2 and 3, the PI will participate in the UW Ram Test Field Day to present results. Additionally, a one-page summary will be distributed to all Ram Test producer participants summarizing results. Following the field day, the eight participating producers will receive a follow-up survey to assess gain in RFI knowledge, understanding, and its applications, and to assess continued interest in marker-assisted selection for improved RFI. All other Field Day attendees will receive a survey to assess interest in RFI as a trait of efficiency, and determine interest in participating in future research trials promoting genetic tools for RFI selection. Results from Objectives 2 and 3 will be submitted to a scientific journal for publication. Additionally, all results will be published in regional agriculture publications (i.e. newspapers and circulations) and UW's "Reflections" publication which features ongoing research in the College of Agriculture. Additionally, producers will be kept abreast of research activities and results via the Department of Animal Science website. Results to date will be presented at the Wyoming Stockgrower’s Convention and at the Western Section ASAS meeting each year. Participating producers will receive a $100 credit towards each testing fee (per ram) submitted for their participation efforts. This project is intended to be a primary project of a PhD student under the direction of PI.

For RFI to be successfully adopted by the sheep industry, producers must be educated about its advantages over other efficiency measures and its application within the industry. Marker-assisted selection is becoming of greater interest to producers because of the added accuracy and more rapid response over traditional selection methods. Therefore, markers associated with traits of economic importance to producers must be discovered, and their impacts on animal performance assessed. This project aims to directly involve producers in this process, which will ultimately aid in the adoption of this technology. The combined efforts of both researchers and producers ensures that the results from this project are directly applicable to the sustainability of animal agriculture.

Objectives: The objectives of this project are to 1) assess and improve producer knowledge of RFI and determine the acceptability of RFI adoption as the standard measure of efficiency in sheep; 2) use producer rams on-test (from two sequential ram tests) at UW to determine relationships of RFI with other traits of economic importance, including reproductive performance and carcass merit; and 3) identify genetic markers associated with improved RFI of rams on-test for marker-assisted selection implementation in the long-term. Actions: (Objective 1). Participating producers on this grant will receive a survey assessing their initial knowledge and acceptance of RFI as a measure of feed efficiency (baseline assessment). Producers will also be asked to convey their interest in use of genetic marker tests to improve efficiency, and the cost willing to pay for such tests. (Objective 2). Participating producers have agreed to allow the PI access to performance data generated during each of two test periods, use ultrasound to estimate BF and LEA ,and collect blood samples from rams for genotype analysis. Producers will also provide breeding records to assess reproduction. The PI will use all data to conduct statistical analyses to determine the potential impact of genetic selection for RFI on reproductive performance and carcass merit. (Objective 3). The leptin hormone has a regulatory role in whole-body energy metabolism, and variants in the leptin gene and its promoter have been associated with changes in performance in beef cattle , namely growth rate, feed intake, metabolic body weight, and final slaughter weight. Such variants are likely associated with feed efficiency traits, and although discovered in beef cattle, those variants are likely present in sheep as well (>95% homology). Variants will be confirmed in sheep prior to genotyping analysis, and additional variants discovered will also be included in subsequent analyses. Blood samples collected from participating producer rams will be genotyped for leptin and leptin promoter variants, and those genotypes will be analyzed for associations with RFI. Genotypes with significant association with RFI will be considered potential genetic markers for RFI. The proportion variation in RFI explained by each marker will be estimated to determine those markers with the greatest potential. It should be noted that circulating leptin will not be measured as it is not stable and requires multiple samplings over long time periods.