No abstract

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 1 h, and then returned to the original farm (TRANS); 2) i.v. injection of ACTH, 1 IU/kg BW (ACTH); or 3) walked through the handling facilities (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, Tuli-sired calves were restrained at 10 and 150 d of age for 3.5 h. In Test 2, Brahman-sired calves were restrained for 3.5 h and given an injection of ACTH (.125 IU ACTH/kg of BW). In Test 3, Test-2 calves were restrained at 180 d of age and hot-iron branded. In Test 4, Test-1 calves 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 blood 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 cortisol in Test 1 (restraint) than the ACTH and SHAM calves (P < .01). The ACTH challenge (Test 2) increased plasma cortisol and ACTH, but cow treatment did not alter the response (P > .4). In response to branding (Test 3), the TRANS, ACTH, and SHAM calves' overall mean plasma cortisol was 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 plasma 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 gestation altered their calf's physiological response to stress, and these alterations could have a profound influence on the calfs ability to adapt to stress, thereby influencing its welfare. Further research should examine the growth, immune function, and reproductive function of prenatally stressed calves to determine whether these changes in plasma cortisol are beneficial or deleterious.

The appropriate dose and the ability of exogenous ACTH to mimic the physiological effects of a real stressor need to be determined. In Exp. 1, 25 pregnant Brahman heifers were injected i.v. with either 0 (saline), .125, .25, .5, or 1 i.u. of ACTH/kg BW. Plasma cortisol was determined in blood samples collected during a 5-h period, and an integrated cortisol response was calculated for each cow. The greater the dose of ACTH, the greater was the integrated cortisol response (P < .001). However, peak plasma cortisol in response to the four doses of ACTH did not differ (P > .6). The plasma cortisol concentrations returned to baseline more slowly in those cows receiving the greater doses of ACTH, making their integrated areas of response greater. In Exp. 2, pregnant Brahman cows were either transported 48 km (n = 28), injected with 1 i.u. of ACTH/kg BW (n = 21), or served as shams (n = 28). Each treatment was repeated at 60, 80, 100, 120, and 140 d of gestation. Shrink was greater for the transported cows than for either the ACTH-treated or sham cows, 14.3, 6.0, and 5.2 kg (P < .001). Shrink also decreased in response to each subsequent application of treatment for all three treatment groups (P < .001). Transported cows had lower plasma cortisol concentrations after the first two applications of treatments (P < .006). The range of doses of ACTH caused a similar peak cortisol release; however, it took cortisol longer to return to baseline as ACTH dose increased. Repeated administration of exogenous ACTH did not cause the same amount of shrinkage as transportation, and the resultant cortisol concentrations remained consistent for each administration. There was no apparent carryover effect of repeated administration of ACTH at 20-d intervals. Maximal plasma cortisol concentrations in Brahman cattle can be obtained with doses of ACTH much smaller than those traditionally injected. However, larger doses of ACTH maintained plasma cortisol concentrations for a longer duration. Repeated transportation caused a decrease in cortisol release and shrinkage indicative of psychological habituation. Injections of ACTH did not cause the same physiological response as transportation.

No abstract

Brahman (n = 9) and 1/2 Simmental x 1/4 Brahman x 1/4 Hereford (n = 11) calves were utilized to determine the influence of exposure to cold on the physiology of the neonate. All calves were removed from their dams within 20 min of birth and prior to suckling. Calves were assigned randomly within breed to either a warm (W; 31 degrees C) or cold (C; 4 degrees C) environmental treatment group. Jugular blood samples were collected via indwelling catheters at 20-min intervals for 180 min. At 100 to 120 min of sampling, all calves were given 1.2 liters of colostrum from their dams via stomach tube. At 120 min, C calves were placed in the W environment. Calf vigor score (CVS) and rectal temperature were determined at each time blood was collected. Serum or plasma was analyzed for glucose (GLU), lactate (LAC), blood urea nitrogen (BUN), hemoglobin (HEM), triglyceride (TRG), triiodothyronine (T3), thyroxine (T4), insulin (INS), cortisol (CORT) and nonesterified fatty acid (NEFA) concentration. Rectal temperature was lower (P less than .01) in C Brahman than in W Brahman and C or W crossbred calves. Crossbred calves had higher (P less than .01) CVS than Brahman calves. Calves in W had lower (P less than .01) GLU than C calves. Brahman calves had higher GLU, LAC, BUN, TRG, T3, T4 and CORT (P less than .05) than crossbred calves. The C Brahman calves had the highest (P less than .05) TRG, CORT, T3 and T4 of all groups. Concentration of NEFA were higher (P less than .01) in C than in W calves.(ABSTRACT TRUNCATED AT 250 WORDS)