Multiparous beef cows (n = 7) were used to evaluate peripartum changes and interactions among body temperature (BT) and circulating progesterone (P4), estradiol-17beta (E2), triiodothyronine (T3), cortisol, thyroxine (T4), and 13,14-dihydro-15-keto-prostaglandin F2alpha (PGFM) concentrations. Electronic temperature monitors were placed under the obliquus abdominis internus muscle of the left flank, and BT was measured using radiotelemetry every 3 min for 10-s periods from 144 h before to 24 h after calving. Environmental temperatures (ET) were recorded hourly. Body and environmental temperatures were averaged, separately, within 8-h periods. Blood samples were collected every 8 h, and hormone concentrations were measured. Time of day affected BT (P < .01), at 0300 cows had the lowest BT, at 1900 the highest, and at 1100 values were intermediate. Body temperature remained relatively constant (P > .10) from 144 to 56 h before calving and from 8 to 24 h after calving but decreased (P < .01) from 48 to 8 h before calving. Precalving BT was affected (P < .01) by ET, but hour-before-calving (time) had the greatest effect on BT during the 48 to 8 h immediately preceding parturition (b' = .41, P < .01) and was independent of ET effects. Before the BT decrease, cows gestating heifers had lower (P < .01) BT than cows gestating bulls. Plasma E2, PGFM, T3, and T4 concentrations before the precalving decrease in body temperature were greater (P < .03) in cows gestating bull rather than heifer calves. Approximately 30% of the variation (R2) during the temperature decrease was explained by plasma hormone concentrations; PGFM (b' = -.30, P < .05) and T3 (b' = -.22, P < .10) had the most significant effects. In conclusion, BT of the cow before the precalving decrease was affected by ET and sex of calf. However, the prepartum BT decrease was independent of these variables, and seemed partially endocrine-induced.

The objective of this study conducted in tropical Brazil was to characterize some physiological responses to heat stress in imported Bos taurus, native Bos taurus, and native Bos indicus cattle. Imported Simmental (n = 107) native Simmental (n = 99), and native Bos indicus cattle (n = 121) (42 to 80 mo of age) were evaluated. Animals were walked 7 km at 37 degrees C and 60 to 65% relative humidity during midday. Rectal temperatures and respiration rates were taken before and after the walk. A .01-cm2 sample of cutaneous tissue from the lateral cervical region was obtained from each animal. Slices were stained with hematoxylin-eosin solution, and the epithelial strata were counted. Perimeter of the sweat glands was also calculated. Rectal temperatures before the walk were greater (P < .001) in imported Simmental (40.52 +/- .04 degrees C) than in native Simmental (38.92 +/- .04 degrees C) or Bos indicus (38.90 +/- .04 degrees C). Rectal temperatures after the walk were greater (P < .001) in native Simmental (39.87 +/- .05 degrees C) than in Bos indicus (39.46 +/- .05 degrees C). Because of the heat, imported Simmental were not capable of finishing the drive, and rectal temperatures could not be taken. Respiration rates before and after the walk were greater (P < .001) in imported Simmental (64.3 +/- .6; 95.8 +/- .8) than in native Simmental (35.0 +/- .6; 56.8 +/- .8) or Bos indicus (15.0 +/- .2; 33.2 +/- .8). Sweat gland perimeter was greater (P < .001) in Bos indicus (540.5 +/- 19.1 mm) than in native Simmental (382.0 +/- 27.6 micrograms) or imported Simmental 497.2 +/- 17.4 micrograms). Native Bos indicus were environmentally adapted, native Simmental had elevated body temperatures and respiration rates, and imported Simmental had dramatically increased body temperatures and respiration rates. Native Bos indicus cattle were environmentally adapted and differed in skin histology, sweat gland histometry, and number of epithelial strata.

Peripubertal beef heifers (n = 57) and postpartum multiparous cows (n = 52) were used to determine the optimal dose of estradiol benzoate (EB) to induce and synchronize estrus after treatment with intravaginal progesterone inserts (IVP4, EAZI-BREED CIDR). All females received an IVP4 for 7 d (d 0 = insertion day) with a 25-mg injection of PGF2alpha (Lutalyse) on d 6. At 24 to 30 h after IVP4 removal, females were randomly assigned to be injected subcutaneously with EB at the following doses: heifers 0, .2, .38, or .75 mg and cows 0, .25, .5, or 1 mg. Furthermore, seven heifers and seven cows from each dose group were bled every 4 h for 76 h starting at EB injection. Serum was collected and assayed for LH and estradiol-17beta (E2). Observations for signs of estrus were made twice daily for 21 d after removal of IVP4, and females were artificially inseminated 8 to 20 h after detection of estrus. The percentage of females showing estrous behavior was increased by EB (P < .04); the greatest response was at .38 mg in heifers (86%) and 1 mg in cows (100%). Dose x time interaction affected (P < .01) E2 concentrations in heifers and cows; the animals that received the higher doses of EB had greater E2 concentrations in a shorter time than those that received the smaller doses. The percentage of cows and heifers with an acute preovulatory LH release (peak LH) was affected by dose, with a linear (P < .01) and a quadratic (P < .01) response. Highest concentrations of LH during peak LH were affected by dose with a linear (P < .01) response in heifers and linear (P < .01) and quadratic (P < .08) responses in cows. Heifers receiving .38 mg and cows receiving .5 and 1 mg of EB had the highest peak LH. Time to LH peak had a linear (P < .03) response in heifers and had linear (P < .04) and quadratic (P < .05) responses in cows. Pregnancy rate was affected (P < .02) in heifers by whether or not they were anestrous before IVP4 treatment (those with estrous cycles = 52% vs those that were anestrous = 22%) and in cows by dose of EB (P < .01; 8, 23, 21, and 67% for 0, .25, .5, and 1 mg, respectively). In conclusion, in females treated with IVP4 and PGF2alpha to induce and synchronize estrus, an injection of EB increased concentrations of E2 and LH and increased number of animals showing estrus. Also, EB increased pregnancy rates in cows. Optimal responses were at .38 mg EB for heifers and at 1 mg EB for cows.