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This study evaluated the influence of cow age and temperature adjusted for windchill (Twindchill) on supplement intake behavior of cattle winter grazing northern mixed-grass prairie rangelands. A commercial herd of 291 (yr-1) and 316 (yr-2) bred cows were winter grazed on a 329-ha rangeland pasture for 2 years. Cows were assigned to one of six age classifications and were provided free-choice access to Rumax Bovibox HM (2018–2019) and Rumax Bovibox (2019–2020) protein blocks. The target daily intake range was 0.45–0.91 kg∙cow-1∙d-1. Supplement was provided in a SmartFeedPro self-feeder system to measure individual animal supplement intake and behavior. Average daily supplement intake (expressed as kg∙cow-1∙d-1) and variation in supplement intake displayed Twindchill × cow age × yr interactions (P ≤ 0.05). There was no effect of age on daily supplement intake at below average and above average Twindchill in yr 1 (P ≥ 0.07). Age displayed a quadratic effect on daily supplement intake at average Twindchill in yr-1 (P < 0.01) but was limited to 3- and 4-yr-old cattle consuming more supplement per day than yearlings (P ≤ 0.02). During yr-2, cow age had a quadratic effect on supplement intake for all Twindchill conditions (P < 0.01) where 3-yr-old cattle consumed more supplement per day than yearlings, 5–7- and ≥ 8-yr-olds (P ≤ 0.01). Cow age exhibited quadratic effects on variation in supplement intake across all Twindchill conditions during both years (P < 0.01). However, the quadratic effects of age in yr-1 were limited to yearlings having higher variation in supplement intake than all other ages (P < 0.01). In summary, both cow age and the winter environmental conditions interacted to influence animal supplement intake behavior and, as a result, nutrient delivery efficacy in winter grazing beef cattle.

The objectives of this study were to evaluate Rumax BoviBox versus Rumax BoviBox HM protein supplements on supplement intake behavior, body weight (BW), and body condition score (BCS) change of yearling heifers grazing dryland pastures during late summer. Fifty-nine yearling commercial Angus heifers (428 kg) were stratified by BW and randomly assigned to one of two supplementation treatments: 1) free-choice access to Rumax BoviBox protein block supplement (30% CP, 23% salt; n = 29); and 2) free-choice access to Rumax BoviBox HM high magnesium protein block supplement (28.7% CP, 23% salt; n = 30). Individual supplement intake, time spent at the feeder, and intake variation were measured throughout the study. On d 0, 42, and 84 heifers were weighed and assigned a BCS following a 16-h shrink. Additionally, forage was sampled every 14 d throughout the study. Supplement intake (kg ∙ d-1) displayed a treatment × period interaction (P < 0.01). However, within period, treatment differences were not observed with intakes averaging 0.15 and 0.34 kg ∙ day-1 for d 0 – 42 and 42 - 84, respectively. Heifers spent more time at the feeder in period 2 than in period 1 (P < 0.01), averaging 7.67 vs 4.00 min per day, respectively. Supplement intake rate (g ∙ min-1) also displayed a treatment effect (P < 0.01) indicating that heifers in the Rumax BoviBox treatment had lower intake rate compared to Rumax BoviBox HM supplemented heifers. In conclusion, there were only minor differences in intake behavior and animal performance with the Rumax BoviBox and Rumax BoviBox HM supplement treatments. However, supplement intake increased and variation in intake decreased with declining forage quality and quantity.