Impacts of age on residual feed intake and its effect on reproductive parameters and profitability in ewes

Project Overview

Project Type: Graduate Student
Funds awarded in 2011: $24,990.00
Projected End Date: 12/31/2012
Grant Recipient: University of Wyoming
Region: Western
State: Wyoming
Graduate Student:
Major Professor:
Dr. Kristi Cammack
University of Wyoming

Annual Reports


  • Animals: sheep


  • Animal Production: general animal production


    Feed intake measurements were collected on Targhee x Rambouillet (n = 61) ewes to determine residual feed intake (RFI) ranking. Effects of diet on growth, intake and RFI ranking were determined. Ewes were further selected to measure reproductive efficiency based on their forage ration RFI ranking: highly efficient (LRFI; n = 6), moderately efficient (MRFI; n = 6) and lowly efficient (HRFI; n = 6). Surveys from Wyoming sheep producers were used to evaluate producer knowledge of RFI, willingness to incorporate RFI into current breeding strategies, adoption of new technology, and to determine the economic impacts of RFI selection.


    For residual feed intake (RFI) to be an appropriate measure of feed efficiency, it must not be unfavorably associated with traits of economic significance such as carcass merit, growth traits or reproductive efficiency. Research has suggested that RFI is independent of carcass and growth traits (Koch et al. 1963; Francois et al. 2002; Baker et al. 2006), but little information is available on the relationship with reproductive performance. Redden et al. (2010a) reported RFI ranking differences in Targhee ewes (9 months and 13 months age) tested on a pelleted grower diet (16% CP) compared to a chopped grass hay maintenance diet (8% CP). However, it is unknown if differences were due to size of feedstuffs used, growth stage of the ewes or type of diet. Furthermore, Redden et al., (2010b) suggested that selection for low RFI in ewes resulted in unfavorable reproductive efficiency as more efficient ewes produced less offspring than less efficient ewes, and twin born ewes were less efficient than their contemporaries. Cattle, swine and poultry industries have extensively researched the effects of RFI; however, little information is available on the economic repercussions associated with incorporating RFI into individual breeding programs.

    In cattle, selection for feed efficiency could result in a 9-10% reduction in maintenance costs, 10-12% decrease in feed intake and 25-30% reduction in methane emissions (Nkrumah et al., 2006; Hegarty et al., 2007). We hypothesized that RFI ranking would differ in ewes fed a concentrate versus a forage-based diet, and that reproductive measures would differ in ewes more or less feed efficient. Furthermore, economic estimates for cattle may differ from sheep as the two industries differ greatly in structure and breeding emphasis.

    Project objectives:

    Objective 1. Determine how age affects RFI ranking.

    Objective 2. Estimate heritability of RFI in sheep and determine the impact of selecting for RFI on reproductive efficiency.

    Objective 3. Investigate the economic impacts of RFI selection on the sheep industry.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.