Effects of breed on preferential intake of hydroxychloride and sulfate sources of trace minerals in growing beef heifers.

This study evaluated the effects of breed on voluntary preferential intake of two sources of Cu, Mn, and Zn when added to white salt-based trace mineral supplement (days 0 to 55; experiment 1) and protein supplement (days 56 to 112; experiment 2). On day 0, Nelore and ½ Angus × ½ Nelore heifers ( n  = 20/breed) were stratified by breed, body weight (BW = 347 ± 82 kg), and age (12 to 30 mo), and randomly allocated into 1 of the 40 drylot pens (1 heifer/pen). Both experiments were divided into washout (days 0 to 27 in experiment 1 and days 56 to 83 in experiment 2) and preferential intake periods (days 28 to 55 in experiment 1 and days 84 to 112 in experiment 2). During the respective preferential intake period, heifers were provided simultaneous free-choice access to sulfate (SUL) and hydroxychloride (HYD) sources of Cu, Mn, and Zn mixed into salt-based trace mineral supplements from days 28 to 55 (experiment 1) and then protein supplements from days 84 to 112 (experiment 2). Heifers were provided free-choice access to Tifton 85 ( Cynodon sp. ) hay from days 0 to 112. Effects of breed × source × day of the study were detected ( P  ≤ 0.05) for daily trace mineral intake from days 28 to 56 and days 84 to 112. Angus × Nelore heifers consumed a greater amount of SUL vs. HYD supplements on days 31 to 33 ( P  = 0.02) and HYD vs. SUL supplements on days 37 to 42 ( P  ≤ 0.02), whereas Nelore heifers consumed more HYD vs. SUL supplements on days 31 to 33 and 43 to 51 ( P  ≤ 0.05). Both breeds consumed ( P  ≤ 0.05) a greater amount of protein supplement containing HYD vs. SUL from days 84 to 112, but the differences in protein supplement intake increased ( P  ≤ 0.04) in greater magnitude for Nelore vs. Angus × Nelore heifers. Supplement intake coefficient of variation (CV) from days 28 to 41 and days 84 to 97 tended ( P  = 0.06) to be greater for Nelore vs. Angus × Nelore heifers. Effects of breed × source were detected ( P  = 0.02) for supplement intake CV from days 84 to 112. Intake CV of supplements added with HYD did not differ ( P  ≥ 0.40) between Nelore vs. Angus × Nelore heifers but was greater ( P  < 0.01) for Nelore vs. Angus × Nelore heifers fed SUL supplements. Overall, Nelore heifers had greater preferential intake for mineral and protein supplements containing hydroxychloride vs. sulfate sources compared to Angus × Nelore heifers. Hydroxychloride sources encouraged voluntary intake and reduced variation in supplement consumption compared to SUL sources of the same metals.