41. Comparison of Mineral Tub Supplementation Containing Either Organic-complexed or Inorganic Trace Mineral Sources on Heifer Development and Reproductive Performance.

Abstract Replacement heifer development programs aim to prepare females for reproductive success by using targeted nutritional and management techniques, such as mineral supplementation. Mineral nutrition, although commonly overlooked, plays a key role in meeting physiological demands, and trace minerals are often provided in different forms, including organic and inorganic sources, to support heifer development. The objective of this study was to compare beef heifer growth and reproductive performance when supplemented with mineral tubs containing organic-complexed or inorganic trace mineral sources offered for ad libitum consumption. Thirty days after weaning, fall-born, commercial Angus heifers (n = 80) were allocated randomly to 1 of 8 pastures based on weaning body weights, birth weight, birth date, and sire. These 8 pastures were then assigned randomly to 1 of 2 treatment groups: 1) supplementation with tubs containing organic-complexed trace minerals (ORG) or 2) supplementation with tubs containing inorganic trace minerals (ING), with both containing similar micromineral concentrations. Mineral tubs and white salt were weighed and placed into pastures on d 0 (May 14, 2025), and mineral intake was determined by measuring tub weights weekly. Growth performance data, including body weight (BW) and body condition score (BCS), were collected monthly. Estrus synchronization for artificial insemination (AI) began on d 187. All heifers were bred to male-sexed semen from a single sire either 12 hours after observation of standing heat or by fixed-time artificial insemination (FTAI) at 66 hr (d 205). Ten days after FTAI (d 215), heifers were combined into groups (n = 20) within mineral treatment and exposed to 1 fertile bull per pasture. FTAI and overall pregnancy rates were determined by blood analysis (d 238 and d 292). Performance data were analyzed using the MIXED procedure and pregnancy data were analyzed using the GLIMMIX procedure in SAS 9.4. A day effect was observed for BW and BCS (P < 0.0001), indicating that heifers increased in BW and BCS throughout the study, but no differences were detected between treatments (P ≥ 0.2661) or treatment × day interactions (P ≥ 0.9372). There was a treatment × day interaction (P < 0.0001), a main effect of treatment (P = 0.0131), and a day effect (P < 0.0001) for mineral intake. Overall mineral intakes were greater for heifers receiving ORG supplement (290 g/d) in contrast to the heifers on the ING supplement (371 g/d). No differences were detected for AI pregnancy status (P = 0.6557; ORG = 55%, ING = 50%). Additionally, overall pregnancy rates did not differ between treatments (P = 0.4461; ORG = 91%, ING = 88%). In conclusion, trace mineral source affected mineral intake, but did not alter performance or pregnancy outcomes in developing beef heifers.