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.
Keywords: beef cattle; cow age; grazing behavior; residual feed intake (RFI), resource use; supplement intake.