PS4-14. Influence of Additional Organic-complexed Zinc in Supplements for Beef Cows During Gestation: Effects on Preweaning Health of Offspring.

Abstract The objective of this study was to determine effects of additional a zinc organic-complexed supplement for gestating beef cows on calf performance. In May 2025, Angus crossbred cows confirmed pregnant with female sexed semen (n = 83) were allotted to 4 groups (20 to 21 cows/group) based on, sire, cow age, and cow body weights taken at weaning of the previous calf. Groups received 1 of 2 treatments (2 groups/treatment): 1) being a grain supplement with inorganic zinc (Zn) to meet current NASEM requirements (INGZN), and 2) being a grain supplement containing an additional 369 mg/d of Zn as an amino acid complex (Zinpro Availa Zn) (ORGZN). The supplement was offered at a rate of 1.36 kg/cow each day which began on d 160 of gestation. Before calving, a subset of cows (n = 32; 16 cows/treatment) were transferred to a closer working facility for intensive sampling procedures. Cows were provided with 2.43-ha grass paddocks where routine calf checks occurred. At parturition, the cow-calf pair was left alone until the calf stood and suckled once, then were moved to a working barn for sample collection from the dam. While restrained in the chute, blood samples were collected via jugular venipuncture and transition milk samples were collected from each quarter and composited for each cow. Birth weights and morphometric measurements were recorded for each calf. At 48 hours following parturition, calves were restrained and blood samples were collected. Calf whole blood samples were utilized for a complete blood cell (CBC) analysis. Milk and serum samples were further analyzed for immunoglobulin A and G concentrations. All data were analyzed using MIXED and GLIMMIX procedures of SAS 9.4 with sire and location as random effects and group being the subject. Dietary treatments had no effect on birth weights (P = 0.28; INGZN = 29 kg vs. ORGZN = 30 kg). The number of cows that remained open (n = 6 vs. 2) and the number of calves that died (n = 5 vs. 3) were not affected by treatment but were numerically greater for INGZN cows (P ≥ 0.22). Calf morphometric measurements recorded at birth were not different between treatments (P ≥ 0.16). The number of basophils tended to be greater (P = 0.09) for the calves on the ORGZN (0.17 K/µL) when compared to calves on the INGZN (0.09 K/µL). No treatment differences were observed in calf serum (P ≥ 0.23) or transition milk immunoglobulins (P ≥ 0.45) A or G. To conclude, organic-complexed Zn supplementation during gestation had minimal effects on calf birth weight, immunoglobulin concentrations, or blood counts near birth, however calves will continue to be monitored for potential effects as calves age.