Abstract The objective of this study was to evaluate the effect of supplemental calcidiol (HyD; DSM Nutritional Products, Pendergrass, GA) on circulating metabolites and the anabolic response to an implant in receiving cattle subjected to an 18-hour transit event. Angus crossbred steers n = 48; body weight (BW) = 273 ± 9 kg were enrolled in an 89-d receiving study, housed in pens of 6, with one GrowSafe bunk (GrowSafe Systems, Ltd, Airdrie, AB, Canada) in each pen and fed a corn silage-based growing ration. A 2 × 2 factorial design was used to assess the effects of calcidiol supplementation CON (no supplemental vitamin D3) or HYD (0.5 mg calcidiol per steer daily starting d -33 relative to transit) and implant NOIMP (no implant) or IMP (Synovex Choice, Zoetis; 100 mg trenbolone acetate and 14 mg estradiol benzoate; d 9 relative to transit). Body weights and blood were collected on d -33, -15, -1, 0 (on-truck, no blood collected), 1 (off-truck), 3, 9, 30, and 56. Data were analyzed in Proc Mixed of SAS 9.4 as a 2 × 2 factorial with the fixed effects of HYD, IMP, and their interaction; steer was the experimental unit (n = 12 per treatment). Blood parameters were natural log transformed and analyzed with day relative to transit as the repeated effect. Prior to transit, no differences due to HYD were noted for BW, dry matter intake (DMI), average daily gain (ADG), or gain:feed (G:F; P ≥ 0.12). During the post-transit period, IMP tended to improve d 30 BW (P = 0.06) and improved d 56 BW (P = 0.04). Post-transit ADG was affected by HYD × IMP (P = 0.03) where HYD-IMP exhibited greater ADG than all three other treatments (P ≤ 0.02), and CON-IMP did not differ from CON-NOIMP (P = 0.36). Post-transit G:F was affected by HYD × IMP (P 0.01) where HYD-IMP was greatest (P 0.01) and CON-IMP did not differ from CON-NOIMP (P = 0.18). Serum 25(OH)D3concentrations were affected by HYD × Day (P 0.01), where CON and HYD were similar on d -33 (P = 0.72; mean 22.8 ng/mL), but HYD increased serum 25(OH)D3 during the pre-transit period (P ≤ 0.03), while CON decreased (P 0.01). Serum 25(OH)D3 were steady for both treatments during the post-transit period (P ≥ 0.14; HYD and CON means = 105.0 and 12.1 ng/mL, respectively). Serum non-esterified fatty acid concentrations were greatest immediately off-truck but returned to baseline by day 9 (day P 0.01). Control steers had minimal response to implant post-transit, while HYD-IMP cattle exhibited greater ADG and G:F. This suggests HyD supplementation may be beneficial in supporting the response to growth-enhancing technologies in stressed receiving cattle.
Henderson et al. (Wed,) studied this question.