Duration of restraint and isolation stress as a model to study the dark-cutting condition in cattle.
The duration of restraint and isolation stress (RIS) on endocrine and blood metabolite status and the incidence of dark-cutting LM were assessed using Holstein steer calves. Treatments included unstressed controls (NS), or a single bout of RIS for 2, 4, or 6 hours. Serum cortisol and plasma lactate increased during the first 20 minutes after the RIS application and remained high throughout the 6 hours of RIS. Plasma glucose and insulin concentrations were greater for RIS calves than NS calves after 80 and 100 minutes of stressor application respectively. RIS did not affect plasma NEFA concentrations. Slaughter occurred within 20 minutes of completion of RIS. The pH of the LM from calves subjected to 6 hours of RIS was greater than 6.0 and was higher than that of NS calves and 2 and 4 hour RIS calves 24 and 48 hours post mortem. Concentrations of muscle glycogen did not differ between the treatments and the LM lactate concentrations tended to be lower in calves subjected to 6 hours of RIS. The LM of calves subjected to 6 hours of RIS had more bound and less free moisture than the LM from NS calves and calves subjected to 2 or 4 hours of RIS at 48 hours after exsanguination. Furthermore, the LM from RIS calves was darker than the LM of NS calves. Calves subjected to 6 hours of RIS had the greatest visual color scores for the LM and NS calves had the lowest. Cases of dark-cutting resulted from calves in all treatments except the NS treatment. Therefore, RIS may have been proven to be a reliable animal model with which to study the formation of the dark-cutting condition.
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