The Influence of Residual Feed Intake and Cow Age on Beef Cattle Performance, Supplement Intake, Resource Use, and Grazing Behavior on Winter Mixed-Grass Rangelands

SIMPLE SUMMARY: Feed efficiency is becoming an important selection tool in the beef cattle industry. Traditionally, feed efficiency of beef cattle has been expressed as the ratio of feed intake to body weight gained; however, selection for high growth rates inevitably increases the maintenance requirements, feed requirements, and intake of cattle, with subsequent higher feed costs. In contrast, net feed efficiency, or residual feed intake (RFI), is defined as the difference between an animal’s actual feed intake and its expected feed requirements for maintenance and growth, with low-RFI animals being more efficient at converting forage intake into kilograms of production than high-RFI animals. This study evaluated the impacts of cow age and RFI on body weight (BW) and body condition score (BCS) change, supplement intake, grazing behavior, and resource use of grazing beef cattle grazing mixed-grass rangelands. Heifer post-weaning RFI had little effect on subsequent performance (BW or BCS), grazing behavior, supplement intake behavior, or resource use. However, cow age significantly influenced subsequent performance, grazing behavior, supplement intake behavior, and resource use. In summary, post-weaning RFI had minimal effects on beef cattle performance, grazing behavior, or resource utilization; however, cow age impacted both grazing behavior and resource use. ABSTRACT: The objectives of this study were to evaluate the influence of RFI and cow age on the supplement intake and grazing behavior of beef cattle. Average daily supplement intake (kg/cow/d) displayed an RFI × cow age interaction (p < 0.01), with a linear increase in average daily supplement intake with increasing RFI of 3-year-old cows (p < 0.01). Average daily supplement intake (g ∙ kg BW(−1) ∙ d(−1)) displayed an RFI × cow age interaction (p < 0.01), with a quadratic effect on supplement intake of 3-year-old cows (p = 0.01). Cow age displayed a quadratic effect on variation of supplement intake (p < 0.01), where 1-year-old cows had a greater CV of supplement intake than all other cow ages (p < 0.01). Distance traveled displayed a cow age × RFI interaction (p = 0.02), where high-RFI 5-year-old cows traveled further per day than low 5-year-old RFI cows. The probability of grazing site selection was influenced by cow age (p ≤ 0.03). In summary, heifer post-weaning RFI had minimal effects on beef cattle performance, grazing behavior, or resource utilization; however, cow age impacted both grazing behavior and resource use.