Effects of pre-weaning feed supplementation and total versus fenceline weaning on the physiology and performance of beef steers

Forty-eight Angus steers (208 ±15 days of age) housed on pasture with their dams, were divided equally based on initial body weight (BW; 312 ± 28 kg), and assigned randomly to assess whether receiving a palatable, high fiber supplement (YS; 4.5 kg/cow-calf/day) versus no supplement (NS) for 7 days prior to weaning alters the steers’ acute stress response following separation from its dam. Steers were weaned (day 0) by fenceline (FS; 12 NS and 12 YS) or total separation (TS; 12 NS and 12 YS). On day 7 the FS group was moved to a pasture lot distant from their dams and adjoining the TS group. All steers were weighed and bled on days -7, 0, 3, 7, 14, and 35 (BW only) and provided access to the supplement on days 0 to 14. By day 0, BW gain increased (P<0.01) and serum interferon-γ (IFN-γ) concentration decreased (P<0.01) in all steers. However, the YS steers exhibited greater (P<0.05) neutrophil to lymphocyte (N:L) ratio and total plasma cortisol (CORT; P=0.09) and ceruloplasmin (CER; P=0.08) concentrations compared with NS steers. From weaning to day 7, NS-TS steers initially experienced a BW loss (P<0.01) followed by a BW gain (P<0.01) when compared with the remaining steers. At 3 day post-weaning, mean hematocrit for YS steers was lower (P < 0.01) than that of NS steers and CORT was greater (P<0.05) for NS-TS vs. YS-TS steers. Red blood cell number, N:L ratio, haptoglobin and IFN-γ concentrations increased (P<0.01) in all steers by day 3 and returned to pre-weaning concentrations thereafter. From days 14 to 35, NS-FS steers gained less (P<0.01) weight compared with YS-FS and all TS steers. These results suggest that providing a high fiber supplement beginning from 7 days prior to weaning may reduce BW loss and temper the steers' acute stress response when weaned using total separation.   Key words: Beef steers, pre-weaning supplementation, stress.