Residual Feed Intake - Producer Adoption and Genetic Selection Potential

Residual Feed Intake - Producer Adoption and Genetic Selection Potential

Summary

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 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.

Objectives/Performance Targets

The objectives of this Western SARE Professional + Producer funded proejct 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 at least 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.

Accomplishments/Milestones

One PhD student is currently working on this project as part of her dissertation work. To date, we have accomplished objectives 1 and 2.

Objective 1: Producers (n = 17) completed surveys regarding their knowledge of RFI and their interest in it being a potential selection criterion. A critical part of establishing RFI as a selection criterion is producer support and understanding. Our surveys indicate that producers are very interested in RFI and other feed efficiency traits. Producers received information sheets describing RFI and how genetic selection strategies could be implemented. Additionally, producers received a summary of how each of their rams performed in their respective Ram Test, including RFI measurements and rankings. We had more producers interested in participating than anticipated. Participating producers received a $100 credit per ram submitted to the Ram Test for their efforts.

Objective 2: In both the dual-purpose breeds and the meat breeds, there was no effect of RFI ranking on backfat, loin eye area or body condition score. The dual-purpose breeds did show a tendency towards more efficient rams (lower RFI values) to have smaller scrotal circumferences; however, there was no relationship between RFI and scrotal circumference in the meat breed rams. Scrotal circumference is a correlated trait with age of daughters at puberty as well as an indicator of growth. Additional research will be required to elucidate the effects of selecting for RFI on scrotal circumference. There were no relationships between RFI values and fleece characteristics (grease fleece weight, clean fleece weight, fiber diameter, staple length, wool grade and belly wool score) in the dual purpose breed rams, nor were there any relationships with face and wrinkle scores.

Objective 3: DNA has been extracted from blood samples and is currently be prepared for genetic analysis. We will be working with colleagues at the USDA Meat Animal Research Center (Clay Center, NE) to better identify potential SNPs in the leptin gene and promoter. Resulting SNP information will be analyzed for associations with not only RFI but other efficiency traits to determine potential for marker-assisted selection. In addition, previously identified SNPs near the leptin gene will be tested in-house for associated with RFI and feed efficiency traits.

Impacts and Contributions/Outcomes

We have successfully introduced RFI as a measure of feed efficiency to Ram Test producers and have worked with individual producers on incorporating RFI measurements into their selection decisions. We have been able to demonstrate that RFI selection will not negatively affect other economically important traits, an important finding to ensure producer adoption of this trait. We have published one abstract for the 2011 ASAS National Meeting and one proceedings paper at the 2011 WSASAS regional meeting summarizing results to-date. A manuscript is currently in progress for the Journal of Animal Science, as well as an additional abstract for the 2012 Joint National ASAS and WSASAS meeting. In addition, an annual report detailing this work was published in the University of Wyoming’s Animal Science Department Annual Report. The PhD student has presented results at the annual Rambouillet Association meeting in 2011 and plans to summarize results at the annual meeting in March 2012. Finally, the PhD student has been invited to speak at the American Sheep Institute’s annual meeting (January 2012) regarding selection potential for RFI in sheep.

Collaborators: