During the first 3 d following weaning, steers fitted with the antisuckling device and fenceline separated (YDFS) lost BW (P < 0.01) compared with device-fitted and total-separated (YD-TS) steers, and together the FS group gained less (P < 0.01) than the TS group (0 vs. 5.7 kg; SEM = 2.0; Table 2). From d 3 to 7, regardless of degree of separation, BW gain was greater (P < 0.05) in ND steers compared with YD steers (4.8 vs. 1.5 kg; SEM = 1.1). This is in contrast to that reported by Haley et al. (2005), where 2-stage calves experienced greater ADG than control calves during the week following weaning by abrupt separation. However, 1 wk following total separation (d 14), the FS steers gained more (P < 0.01) than the TS steers, and from d 14 to 35 the YD-TS steers gained more (P = 0.02) than the YD-FS steers. Overall BW gain during the postweaning period (d 0 to 35) was similar (P = 0.30) between FS and TS steers but tended to be greater (P = 0.07) for YD-TS steers compared with YD-FS steers. Price et al. (2003) reported that fenceline-separated calves were heavier than total separated calves at 10 wk following weaning. In the present experiment, calves were weighed up to 5 wk following weaning; therefore, we do not know if fenceline-separated calves compensated in weight gain during the following weeks. Our findings suggest that use of an antisuckling device may improve growth performance of calves weaned by total separation.
The HCT did not differ between treatments within each sampling period before or following weaning (data not shown). However, within the YD-treated steers, HCT on d -4 was greater (P = 0.04) than that measured on d -7 and 0 (34.7 vs. 33.3 and 33.2%, respectively; SEM = 0.6). An elevated HCT can be indicative of dehydration (Wright et al., 2000), which may be associated with reduced fluid intake from the elimination of nursing or consumption of water; however, we cannot confirm that this was the case for the YD steers. Our results may imply that once the steers became accustomed to the device, they increased their water intake thus lowering their HCT. However, water intake was not measured in this experiment. Following weaning, all steers experienced a decrease (P < 0.05) in HCT from d 3 to 7 (32.4 vs. 31.6%; SEM = 0.5). No differences were found between FS or TS steers for HCT measured from d 0 to 35.
Lymphocyte percentage decreased (P < 0.01) in all steers from d -4 to 0 (72.4 vs. 66.6%; SEM = 1.8) and tended (P = 0.07) to be lower for YD compared with ND steers on d 0 (63.2 vs. 70.0%; SEM = 2.5). Lymphocyte percentage remained lower (P = 0.09) for YD compared with ND steers on d 3 (60.6 vs. 66.4%; SEM = 2.8) and d 7 (64.6 vs. 71.5%; SEM = 2.8) but was similar to the average lymphocyte percentage of the ND group measured on d 14 and 35 (70.2%; SEM = 2.0). Regardless of treatment, neutrophil percentage increased from 25.6% on d -7 to 31.1% on d 0 and decreased to 25.4% by d 35 (P < 0.05; SEM = 1.7). The resultant N:L ratio increased from d -4 to 0, peaked on d 3, and decreased by d 7 (P < 0.01; Tables 1 and 2). The YD steers exhibited an overall greater (P < 0.05) mean N:L ratio postweaning compared with ND steers (0.49 vs. 0.39; SEM = 0.03), which was particularly evident on d 3 and 7 (Table 2).
Plasma Cortisol concentrations measured before weaning were not different (P = 0.56) between steers with or without the antisuckling device (Table 1). Over time, plasma Cortisol concentration was greater (P < 0.01) in all steers on d -7 and 0 compared with d -4 (Table 1), and d 0 compared with d 7, 14, and 35 (Table 2). Cortisol concentrations can increase in cattle within 20 min following physical restraint (Lay et al., 1992), but the response can be moderated in animals habituated to both the restraining and sampling environment (Hopster et al., 1999; Hickey et al., 2003). On d 7, plasma Cortisol was greater (P < 0.05) in the YD-FS steers compared with the ND-FS steers (Table 2). The time and treatment x time differences in N:L ratio as noted above exhibit a pattern subsequent to those noted for Cortisol concentration. An increase in the N:L ratio associated with neutrophilia has been reported in cattle 48 h following injection of dexamethasone (Anderson et al., 1999) and within 24 to 48 h following abrupt weaning (Hickey et al., 2003; Lynch et al., 2010a,b).
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