EFFECTS OF PRENATAL STRESS ON SUCKLING CALVES

Pregnant Brahman cows (n = 42), bred to either Brahman or Tuli bulls, were randomly assigned to one of three treatments: 1) transported in a stock trailer for 24.2 km, unloaded at a second farm and penned for I h, and then returned to the original farm (TRANS); 2) i.v. injection of ACTH, I IU/kg BW (ACTH); or 3) walked through the handling faciliti es (SHAM). Treatments were initiated on d 60 and repeated at 80, 100, 120, and 140 d of gestation. The calves from these cows were subjected to tests to measure their capacity to react to stress. In Test 1, Tul i-sired calves were restrained at 10 and 150 d of age for 3.5 h. In Te st 2, Brahman-sired calves were restrained for 3.5 h and given an inje ction of ACTH (.125 IU ACTH/kg of BW). In Test 3, Test-2 calves were r estrained at 180 d of age and hot-iron branded. In Test 4, Test-1 calv es were restrained at 180 d of age and given an injection of cortisol (6.7 ng/kg BW) to estimate cortisol clearance rate. During all tests, calves were restrained for 3.5 h, and heart rates were recorded and bl ood samples were taken at -15, 0, 15, 30, 45, 60, 90, 120, and 180 min . The 10- and 150-d-old TRANS calves maintained greater plasma cortiso l in Test 1 (restraint) than the ACTH and SHAM calves (P <.01). The AC TH challenge (Test 2) increased plasma cortisol and ACTH, but cow trea tment did not alter the response (P >.4). In response to branding (Tes t 3), the TRANS, ACTH, and SHAM calves' overall mean plasma cortisol w as not affected by treatment (52, 51, and 43 +/- 3 ng/mL, respectively ; P >.1), nor was the calves' overall heart rate (91, 94, and 86 +/- 3 beats/min, respectively; P >.1). In Test 4, TRANS calves cleared plas ma of cortisol at a slower rate than did the SHAM calves (P <.01), but not the ACTH calves (261, 374, and 473 +/- 50 mL/min, respectively; P >.1). The TRANS calves had an overall greater heart rate than did the ACTH or the SHAM calves (91, 79, and 77 +/- 2 beats/min, respectively ; P <.001). Exposing cows to repeated transportation stress during ges tation altered their calfs physiological response to stress, and these alterations could have a profound influence on the calfs ability to a dapt to stress, thereby influencing its welfare. Further research shou ld examine the growth, immune function, and reproductive function of p renatally stressed calves to determine whether these changes in plasma cortisol are beneficial or deleterious.