Plasma haptoglobin concentration was determined in duplicate samples by measuring haptoglobin/hemoglobin complexing by the estimation of differences in peroxidase activity and read in units of absorption x 100 at 450 nm (
Plasma ceruloplasmin oxidase activity was analyzed using colorimetric procedures as described by Demetriou et al. (1974). Concentrations were expressed as milligrams per deciliter.
Ovalbumin-specific IgG antibody titers in response to inoculation with OVA were detected by ELISA (Engvall and Perlmann, 1972). The optical density values were read at 450 nm using an ELISA reader and expressed as a ratio of a positive control sample on each plate. The positive control sample consisted of pooled blood samples from 2 steers that had been given 2 intradermal injections of OVA in a prior experiment. The intra-and interassay CV were 4.7 and 3.2%, respectively.
Serum IFN-7 was assayed per the manufacturer's protocol using a custom-developed multiplex ELISA validated for bovine cytokines (SearchLight,
Data were analyzed using the MIXED procedure (
RESULTS AND DISCUSSION
Steer BW and physiological response measurements during the pre- and postweaning treatment periods are provided in Tables 1 and 2, respectively. The BW gain was not different (P - 0.74) between the ND and YD steers over the 7 d before separation from their dams (Table 1). Haley et al. (2005) reported that ADG of nursing control calves was greater than that of calves fitted with an antisuckling device for 3, 5 or 14 d before weaning and that calves prevented from nursing for 3 d had a greater ADG than did those that were prevented for the full 14-d period. They suggested that the lower ADG may have been due to poor pasture conditions, reduced number of days calves spent nursing, or both. The calves in our experiment were approximately 2 mo older at weaning than those reported in the Haley et al. (2005) study, and it's been reported beef calves can be naturally weaned by their dams as early as 7 mo of age (Price, 2008). It is possible that our calves may have been self-weaned, making the device inconsequential in discouraging nursing.
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