The effect of season on supplemental mineral intake and behavior by grazing steers

An experiment was conducted to compare individual, free-choice loose mineral intake and feeding behavior by steers grazing pasture during late spring to summer (SS) and fall (FS). Each season was divided into 4 periods of 8 to 9 d. Two 1.5-ha paddocks were equipped with a feeder that measured individual mineral consumption. Forage availabilities in both seasons were maintained above 2,000 kg of DM/ha. No differences were observed (P > 0.05) for average mineral intakes (g/d) between seasons (96.3 vs. 85.4 g/d for SS and FS, respectively). Differences among animals and days within each period were observed (P < 0.05), resulting in a large CV. The CV was lower during SS (77.7) compared with FS (104.3). Supplement intake (g/d) increased (P < 0.05) for each period within season, but no season × period interaction (P > 0.05) was detected. Expressing intake as grams per day is confounded due to differences in animal weight, but when expressed on a metabolic weight basis (MBW), daily mineral intakes differed (P < 0.05) between seasons (1.33 vs. 0.95 g/kg of MBW for SS and FS, respectively). The CV was lower during SS (43.3%) than during FS (51.0%). No correlations (P > 0.05) were detected between mineral intakes (expressed as either g/d or g/kg of MBW) and available forage nutritional composition or IVDMD of clipped forage. In addition, no significant correlations (P > 0.05) were detected between steer ADG, temperature, or rainfall and mineral consumption. Steer attendance at the mineral feeder appeared to be related to intensity of daylight and daily temperatures according to differences in feeder attendance patterns between SS and FS. Results indicate higher mineral supplement intakes and lower CV during SS when expressed on a MBW basis when forage availability was maintained above 2,000 kg/ha.