Effects of prenatal stress on the fetal calf.

Twelve pregnant Brahman cows were randomly assigned to one of two treatment groups: 1) transported in a stock trailer for 24.2 km, unloaded at a second farm and penned for 1 hr, and then returned to the original farm (TRANS, n = 6); or 2) walked through the handling facilities (SHAM, n = 6). Treatments were repeated at 60, 80, 100, 120, and 140 d of gestation. Calves were delivered by cesarean section on d 266 of gestation. The male:female ratio was 4:2 and 5:1 for the TRANS and SHAM treatment groups, respectively. Before calf removal and severance of the umbilical blood flow, a blood sample was collected from the calf to determine plasma concentrations of adrenocorticotropin (ACTH) and cortisol. The calf was then sedated and exsanguinated, after which pituitary and adrenal glands were collected. The adrenals were immediately weighed, and a cross-section from the left adrenal was stored in 4% paraformaldehyde until being embedded in paraffin. Eight sections from each adrenal were sliced (5 microns), fixed, and then stained with Harris' hematoxylin and eosin. Areas of the cortex and medulla were calculated with a computerized digitizing unit and tracing of the viewed section. The TRANS calves had heavier body weights (BW) (28.7 vs. 23.9 +/- 1.8 kg; P < 0.07), pituitary glands (12.63 vs. 8.24 +/- 1.10 g/kg BW; P < 0.008), and heart weights (5.58 vs. 5.17 +/- 0.58 g/kg BW; P < 0.05) than did the SHAM calves. Plasma concentrations of ACTH and cortisol did not differ between SHAM and TRANS calves (57 vs. 82 +/- 14 pg/ml and 7.0 vs. 6.7 +/- 0.9 ng/ml, respectively; P > 0.2). Adrenal gland weight and medulla-to-cortex ratio did not differ between SHAM and TRANS calves (0.61 and 0.73 +/- 0.03 g and 0.97 and 0.99 +/- 0.12 g, respectively; P > 0.2). These results suggest that the altered response to stress in prenatally stressed calves is not associated with morphological changes in the adrenal gland but may be due to effects of prenatal stress on the fetal pituitary.