Effects of pre-transit zinc supplementation and transit duration on performance, metabolites, and feeding behavior of beef steers.

Effects of pre-transit zinc (Zn) supplementation and transit duration on performance, metabolites, and feeding behavior were assessed using 80 Angus-crossbred steers in a 2 × 2 factorial design. Pre-transit diets (DIET) of no supplemental Zn (Zn0; analyzed at 40 mg Zn/kg DM) or 100 mg Zn/kg DM supplemental Zn from ZnSO4 (Zn100) were fed for 42 days. Cattle were assigned to an 8 (8H) or 18 hours (18H) transit duration (DUR). All cattle received Zn100 diet for 56 days post-transit. Steers were stratified by bodyweight (BW) to pens (5 steers/pen) equipped with a GrowSafe® feeding behavior and intake system (Vytelle, Ames, IA USA). Weights were collected on d -42, -41, -1, 0, 1, 2, 7, 28, 55, and 56 relative to transit; blood was collected on d -42, -1, 1, 2, and 7. GrowSafe® feeding behavior data were collected continuously for 7d pre- and post-transit. Data were analyzed using the Mixed Procedure of SAS with DIET, DUR, and DIET × DUR as fixed effects. Feeding behavior, metabolites, and weekly dry matter intakes (DMI) were analyzed as repeated measures with the repeated effect hour, day, or week. Pre-transit average daily gain (ADG), gain: feed (G:F), d -1 BW (DIET P ≤ 0.03) and DMI on weeks 2 and 6 (DIET × Week P = 0.01) were greater for the Zn100 cattle. Shrink was 7.3% for 18H and 5.2% 8H (DUR P < 0.01). Immediately post-transport, 8H cattle had greater serum glucose and insulin, but lesser non-esterified fatty acids (NEFA) than 18H (DUR P ≤ 0.05) cattle. On d 2, 8H had less glucose and NEFA than 18H (DUR P ≤ 0.01), and insulin was not different (DUR P = 0.17). Zn0-18H was the most insulin sensitive on d 1 (DIET × DUR P = 0.01), while 8H was more sensitive than 18H (DUR P = 0.01) on d 2. Feeding duration and frequency were affected by DIET × DUR × Day (P < 0.01). The rate of intake was greater for 8H than 18H at 24, but lesser at 48 and 72 h post-transit (DUR P < 0.01). Time spent at the bunk with head down was greater for 8H at 24, 48, 72, and 144 h post -transport than 18H cattle (DUR P < 0.01). Zn0 cattle had greater post-transit G:F than Zn100 group (DIET P < 0.01). On wk 7, Zn100 had greater weekly DMI, but lesser on wk 12 (DIET P = 0.01). By study's end, performance was not different between treatments (P ≥ 0.11). These data suggest a benefit for Zn supplementation prior to transit on performance, with minimal impacts of transit duration. However, in the short-term, transit duration altered metabolic demand and feeding behavior of beef cattle.