EFFECTS OF PRENATAL STRESS ON THE FETAL CALF

Twelve pregnant Brahman cows were randomly assigned to one of two trea tment 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 origina l farm (TRANS, n = 6); or 2) walked through the handling facilities (S HAM, n = 6). Treatments were repeated at 60, 80, 100, 120, and 140 d o f gestation. Calves were delivered by cesarean section on d 266 of ges tation. The male:female ratio was 4:2 and 5:1 for the TRANS and SHAM t reatment groups, respectively. Before calf removal and severance of th e umbilical blood flow, a blood sample was collected from the calf to determine plasma concentrations of adrenocorticotropin (ACTH) and cort isol. The calf was then sedated and exsanguinated, after which pituita ry and adrenal glands were collected. The adrenals were immediately we ighed, and a cross-section from the left adrenal was stored in 4% para formaldehyde until being embedded in paraffin. Eight sections from eac h adrenal were sliced (5 mu m), fixed, and then stained with Harris' h ematoxylin 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 d id not differ between SHAM and TRANS calves (57 vs. 82 +/- 14 pg/ml an d 7.0 vs. 6.7 +/- 0.9 ng/ml, respectively; P > 0.2). Adrenal gland wei ght 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, respect ively; P > 0.2). These results suggest that the altered response to st ress in prenatally stressed calves is not associated with morphologica l changes in the adrenal gland but may be due to effects of prenatal s tress on the fetal pituitary. (C) Elsevier Science Inc. 1997.