91. Repeatability of Feed Efficiency and Feeding Behavior Across Diets in Katahdin Ewes Divergently Selected for Residual Feed Intake

Abstract Efforts in animal agriculture aim to create a sustainable food supply for the global population. Enhancing feed efficiency and developing measurable metrics to minimize input costs for the small ruminant industry could advance these goals. The Vytelle Sense system allows measurement of individual animal dry matter intake to identify feed efficient animals. The aim of this study was to evaluate if measuring a ewe’s residual feed intake (RFI) while consuming a high energy grain supplement would subsequently predict RFI, daily DMI, and feeding behavior while consuming harvested forages. Katahdin ewes (LowRFI: n = 14; HighRFI: n = 13) previously evaluated on a Vytelle Sense system as lambs to determine RFI classification were mated to Katahdin rams (LowRFI: n = 2; HighRFI: n = 2) at the Virginia Tech Southwest Virginia Agricultural Research and Extension Center (SWAREC). During lactation, ewes were fed a complete pellet (12% CP, 68% TDN) ad libitum for 57 days. Post-weaning, ewes at maintenance were fed harvested forages (12% CP, 58% TDN) ad libitum for 57 days. RFI was calculated as the difference between actual and expected DMI (lactating DMI predicted from ADG, litter weight, and pounds of lamb weaned; maintenance DMI predicted from ADG and body condition score). Feeding duration per meal, DMI per meal, and feeder visit frequency were analyzed to determine feeding behavior. Ewes were categorized as either LowRFI (RFI < 0) or HighRFI (RFI > 0) based on their RFI as a growing lamb. Statistical analyses were performed using the Mixed and Corr procedures of SAS (SAS Institute, Cary, NC). RFI category assigned from her performance as a lamb did not impact ewe predictions while consuming harvested forages at maintenance for daily DMI, G:F, RFI, meal duration, DMI per meal or visit frequency (P > 0.10). However, some correlations exist when assessing the repeatability of these measures across the two dietary test periods comprising of a complete pellet fed during lactation and harvested forages fed during maintenance. There were moderate correlations for daily DMI, RFI, and visit frequency (r = 0.54, 0.43, and 0.42, respectively; P < 0.05) across dietary periods. Approximately 55% of ewes consuming harvested forages remained in their predicted RFI category based on their RFI as a lamb while 59% of ewes remained in the same RFI category between the two dietary test periods (P > 0.10). Variation in RFI prediction indicates the potential for genetic selection to impact feed efficiency with increased selection pressure. Further studies are required to evaluate feed efficiency across diets.