Effect of increasing zinc supplementation on post-transit performance, behavior, blood and muscle metabolites, and gene expression in growing beef feedlot steers

Fifty-four Angus-cross steers (297 kg +/- 12) were stratified by body weight (BW) to pens (six steers per pen) to determine the effects of supplemental Zn on posttransit growth performance and blood and muscle metabolites. Dietary treatments started 25 d before trucking: control (CON; analyzed 54 mg Zn/kg DM), industry (IND; CON + 70 mg supplemental Zn/kg DM), and supranutritional Zn (SUPZN; CON + 120 mg supplemental Zn/kg DM). Supplemental Zn was bis-glycinate bound Zn (Plexomin Zn; Phytobiotics North America, Cary, NC). On day 0, steers were loaded onto a commercial trailer and transported in 18 h (1,822 km). Individual BW was recorded on days -26, -25, -1, and 0 (pre-transit), 1 (posttransit), 6, 27, and 28. Blood was collected on days -1, 1, 6, and 27. Longissimus thoracis biopsies were collected on days -1, 1, and 28. Daily individual feed disappearance was recorded via GrowSafe bunks. Data were analyzed using Proc Mixed of SAS with fixed effect of diet and steer as the experimental unit (growth performance, blood: n = 18 steers per treatment; muscle: n = 12 steers per treatment). Individual initial BW was used as a covariate in BW analysis. Contrast statements to test linear, quadratic, and Zn effects were used to analyze performance and blood parameters. Repeated measures analysis was used for posttransit DMI recovery and weekly posttransit DMI and Zn intake with the repeated effect of time. MetaboAnalyst 5.0 was utilized for statistical analysis of day 1 (off truck) muscle metabolites. Plasma Zn linearly increased due to Zn on days 1, 6, and 27 (P = 0.01), and off-truck (day 1) serum lactate increased over day -1 by 20%, 0%, and 20% in CON, IND, and SUPZN, respectively (Quadratic: P = 0.01). Muscle lactate tended to increase posttransit in CON and IND (P <= 0.07) but not SUPZN. Muscle metabolites relating to amino acid and nitrogen metabolism were increased in all treatments posttransit (P <= 0.02), and alanine-glucose cycle metabolites tended to increase in CON and IND (P <= 0.07). Steers supplemented with Zn recovered pretransit DMI quicker than CON (by d 2: P = 0.01), while IND had greater overall posttransit DMI than CON with SUPZN intermediate (P = 0.04), and Zn-fed steers had greater ADG posttransit (P = 0.04). Zinc supplementation mitigated muscle or serum lactate increases due to transit and increased posttransit ADG. Lay Summary Transportation is an inevitable event in the lives of beef cattle, but practical management strategies could mitigate negative effects of transit on growth performance and cattle welfare. This study investigated the effects of dietary zinc prior to and after trucking on growth performance and blood and muscle metabolites of steers after an 18-h transit event. Steers fed supplemental zinc had better feed intake and growth after transit than steers not fed supplemental zinc. Muscle metabolites relating to energy metabolism were greater posttransit in all steers regardless of treatment. Interestingly, blood and muscle lactate, an indicator of muscle fatigue, was decreased in zinc-fed steers. Supplementing zinc prior to trucking may help mitigate muscle fatigue and improve cattle welfare during the receiving period. Zinc is an essential micronutrient which can increase growth performance and potentially prevent muscle fatigue. Beef steers were supplemented with three concentrations of zinc prior to an 18-h transit event to determine the effects of zinc supplementation on posttransit growth performance and blood and muscle metabolites.