Effects of Hydroxy Trace Mineral Supplementation on Gain and Reproductive Performance in Beef Heifers

Beef heifers previously managed on 3 separate development systems were utilized to assess the effect of trace mineral source on performance and trace mineral status. Two hundred Angus-based, spring-born heifers were stratified by BW and randomly assigned to graze corn residue (CR), upland range (RG), or were fed in a drylot (DL) postweaning. Following the development period, heifers were stratified by development treatment and BW and allocated into 1 of 8 pens per yr. Pens were randomly assigned to 1 of 2 mineral sources, hydroxy (HD, Intellibond, Micronutrients, Indianapolis, IN) or sulfate (CON; Prince Agri Products, Inc., Omaha, NE). Heifers received mineral source treatment for 68 d. Mineral status was analyzed via 2 liver biopsies prior to and following mineral treatment. A development treatment × mineral treatment interaction was observed for initial Cu and Zn status. Heifers developed on drylot and assigned to the CON mineral treatment had greater (P < 0.01) initial Cu and Zn status compared with DL heifers assigned the HD treatment. No development treatment × mineral treatment interaction (P = 0.49) was observed for Mn. Initial trace mineral status was utilized as a covariate in the analysis of final mineral concentrations. No previous development x mineral treatment interaction was observed (P > 0.40) for final Cu, Mn, or Zn. However, CON heifers had a greater (P < 0.01; 208 vs 123 ± 6.1 µg/g, CON vs HD) final Cu status than HD heifers. Mineral source treatment did not affect (P ≥ 0.42) final Mn (10.7 ± 0.32 µg/g) or Zn (143 ± 15.2 µg/g) concentrations. Heifer ADG during the mineral trial did not differ (P = 0.79; 0.68 vs 0.69 ± 0.03 kg, CON, HD) between treatments. Final BW was also not different (P = 0.98; 339 vs 339 ± 3 kg) in heifers fed CON or HD mineral. Pregnancy rates to AI (62 ±5%) and final pregnancy rates (84 ± 4%) were not different (P ≥ 0.89) between mineral sources. Overall, liver Cu concentrations were greater for CON than HD heifers at the end of the trace mineral trial; however, all heifers maintained adequate status throughout the study. The difference in Cu status may be due to ruminally insoluble hydroxy Cu allowing thiomolybdate absorption, thus reducing hepatic Cu stores and resulting in decreased Cu status. Heifer gain and reproductive performance was not affected by mineral source.