Age at weaning and the endocrine response to stress

Seventy-five Angus x MARC II crossbred heifers were used to assess the effects of age at weaning on calf performance and blood constituents. Calves were weaned at 150, 210, or 270 days of age with comparisons made to their non-weaned counterparts. Changes in blood chemistry and hematology (cortisol, glucose, T3, total proteins, packed cell volume and the differential white blood cell count) were recorded on the day of weaning (day-0), and at 2, 7, 14, and 28 days post-weaning. Calves weaned at 210 days of age presented the highest plasma cortisol, glucose, and total protein concentrations during their early post-weaning period. Calves weaned at 150 days of age had significantly lower plasma T3 values. Packed cell volume and differential white blood cell counts showed no relationship to age at weaning. Calves weaned at 210 days of age presented the most rapid post-weaning growth performance, relative to the 150 or 270 days of age weaned calves.