Effect of stress-like concentrations of cortisol on the feedback potency of oestradiol in orchidectomized sheep.

The effect of stress-like concentrations of cortisol on oestradiol-induced change in LH secretion and GnRH receptor expression was evaluated in orchidectomized sheep (wethers). Twenty-four wethers were assigned at random to one of the four treatment groups in a 2x2 factorial design (n=6 wethers/group). Wethers received cortisol (90 microg/kg/h; groups 2 and 4) or a comparable volume of cortisol delivery vehicle (groups 1 and 3) by continuous infusion for 48 h. During the final 24 h of infusion, wethers received oestradiol (6 ng/kg/h; groups 3 and 4) or oestradiol delivery vehicle (groups 1 and 2). The pattern of LH secretion was assessed during a 3-h period of intensive blood collection beginning 21 h after initiation of oestradiol infusion. Although neither cortisol nor oestradiol alone affected (P>0.05) mean serum concentration of LH or LH pulse frequency, serum LH and the frequency of secretory episodes of LH were significantly reduced (P<0.05) in wethers receiving cortisol and oestradiol in combination. Anterior pituitary tissue was collected at the end of the infusion period. Oestradiol increased (P<0.05) tissue concentrations of GnRH receptor and GnRH receptor mRNA. Although cortisol alone did not affect (P>0.05) basal concentrations of receptor or receptor mRNA, the magnitude of oestradiol-induced increase in GnRH receptor and GnRH receptor mRNA was significantly reduced in wethers receiving cortisol and oestradiol concurrently. Conversely, steady-state concentrations of mRNA encoding the LHbeta and FSHbeta subunits were increased (P<0.05) in wethers receiving cortisol. These observations demonstrate that stress-like concentrations of cortisol act in concert with oestradiol to suppress LH secretion. In addition, cortisol blocks oestradiol-dependent increase in pituitary tissue concentrations of GnRH receptor and GnRH receptor mRNA.

Effect of stress-like concentrations of cortisol on gonadotroph function in orchidectomized sheep.

The effect of stress-like concentrations of cortisol (C) on the feedback potency of estradiol (E2) was assessed using 32 orchidectomized sheep (wethers) assigned at random to 1 of 4 treatment groups in a 2 x 2 factorial design. Wethers received C (3. 6 mg/50 kg per hour; groups 2 and 4) or a comparable volume of C delivery vehicle (groups 1 and 3) as a continuous infusion for 7 days. During the final 48 h of infusion, wethers received E2 (0.3 microg/50 kg/h; groups 3 and 4) or E2 delivery vehicle (groups 1 and 2). The pattern of LH secretion was assessed during a 4-h period of intensive blood collection beginning 44 h after initiation of E2 infusion. Gonadotroph responsiveness (LH secretion induced by GnRH challenge [500 ng, i.v.]) was determined 48 h after E2 delivery was begun. Although the frequency of secretory episodes of LH was not affected (p > 0.05) by infusion of C or E2 alone, LH pulse frequency was significantly decreased in wethers receiving C and E2 in combination. In contrast, neither the magnitude of basal gonadotroph responsiveness nor the extent of E2-dependent augmentation of responsiveness was significantly affected by stress-like concentrations of C. In a second experiment, the effect of C on the magnitude of E2-induced increase in pituitary concentration of GnRH receptor and GnRH receptor mRNA was assessed using 32 additional wethers. Continuous infusion of E2 for 48 h increased (p < 0.05) tissue concentrations of GnRH receptor and GnRH receptor mRNA. Concurrent delivery of C did not affect (p > 0.05) E2-induced increase in GnRH receptor mRNA but significantly reduced the magnitude of the E2-dependent increase in pituitary concentration of GnRH receptor. Collectively, these data indicate that stress-like concentrations of C enhance the negative feedback potency of E2 and reduce estrogen-dependent augmentation of the concentration of GnRH receptor in pituitary tissue.

Effect of stress-like concentrations of cortisol on follicular development and the preovulatory surge of LH in sheep.

Stress-like concentrations of cortisol increase the negative feedback potency of oestradiol in castrated male sheep. A similar cortisol-dependent response in female sheep might be expected to suppress gonadotrophin secretion and impair follicular development and ovulation. The oestrous activity of 21 female sheep was synchronized using progestogen-treated vaginal pessaries to test this hypothesis. Stress-like concentrations of cortisol (60-70 ng ml-1) were established by continuous infusion of cortisol (80 micrograms kg-1 h-1; n = 13) beginning 5 days before, and continuing for 5 days after, pessary removal. Control animals (n = 8) received a comparable volume of vehicle (50% ethanol-saline) over the 10 day infusion period. Serum concentrations of oestradiol increased progressively in control sheep during the 48 h immediately after pessary removal. This increase in serum oestradiol was blocked or significantly attenuated in sheep receiving stress-like concentrations of cortisol. Preovulatory surge-like secretion of LH was apparent in control animals 58.5 +/- 2.1 h after pessary removal. In contrast, surge-like secretion of LH was not observed during the 5 days after pessary removal in 54% (7 of 13) of sheep receiving cortisol. Moreover, the onset of the surge was significantly delayed in the cortisol-treated ewes that showed surge-like secretion of LH during the infusion period. The ability of episodic pulses of exogenous GnRH to override the anti-gonadal effect of cortisol was examined in a second study. Oestrous activity of 12 ewes was synchronized using progestogen-containing pessaries as described above. Ewes were randomly assigned to one of three treatment groups (n = 4 ewes per group). Animals received cortisol (100 micrograms kg-1 h-1; groups 1 and 2) or a comparable volume of vehicle (group 3) beginning 5 days before, and continuing for 2 days after, pessary removal. Pulses of GnRH (4 ng kg-1 h-1, i.v.; group 1) or saline (groups 2 and 3) at 1 h intervals were initiated at pessary removal and continued for 48 h. Serum concentrations of oestradiol were not significantly increased after pessary removal in sheep receiving cortisol alone. Conversely, serum concentrations of oestradiol increased progressively during the 48 h after pessary removal in control ewes and in ewes receiving cortisol and GnRH. At the end of infusion, serum concentrations of oestradiol did not differ (P > 0.05) between control (7.7 +/- 0.8 pg ml-1) ewes and ewes receiving cortisol and episodic GnRH (6.4 +/- 1.3 pg ml-1). Moreover, these values were significantly greater (P < 0.05) than the serum concentrations of oestradiol in animals receiving cortisol (1.0 +/- 0.4 pg ml-1) alone. Collectively, these data indicate stress-like concentrations of cortisol block or delay follicular development and the preovulatory surge of LH in sheep. In addition, episodic GnRH overrides cortisol-induced delay in follicular maturation.

Pregnancy status and feedlot performance of beef heifers actively immunized against gonadotropin-releasing hormone.

The contraceptive effect of active immunization against GnRH was evaluated in beef heifers. Crossbred heifers were randomized by breed and weight (initial weight = 227.3 +/- 1.2 kg) and assigned to one of three treatment groups. Animals in Group IB (n = 48) were actively immunized against GnRH; heifers in Groups NB (n = 48) and NN (n = 49) did not receive the anti-GnRH vaccine. Sixteen weeks after primary immunization, bulls of proven fertility were introduced into pens containing Groups IB and NB. Bulls were maintained with heifers for 2 mo. Heifers in group NN were not intentionally exposed to fertile males. At the end of the breeding period, heifers received Synovex H implants and entered a commercial feedlot. Heifers were slaughtered after 116 d of feedlot confinement. Anti-GnRH titer was evident in all heifers (48 of 48) immunized against GnRH. Gravid uteri were present at slaughter in 40 of 48 (83.3%) NB heifers. In contrast, only four (8.3%) IB and two (4.1%) NN heifers carried gravid uteri at slaughter. Although ADG did not differ between groups during feedlot confinement, ADG during the breeding period was higher (P < .05) in IB heifers than in NN control animals. Dressing percentage and longissimus muscle area were decreased (P < .05) and marbling and quality grade were increased (P < .05) in NB heifers compared with NN control heifers. Carcass traits of IB heifers were intermediate between those of the NB and NN groups. Taken together, these data indicate that active immunization against GnRH reduces the fertility of terminal heifers. These observations suggest that immunoneutralization of GnRH may be an effective management tool that will reduce the incidence of unintended pregnancy in heifers destined for feedlots.

Testes function and feedlot performance of bulls actively immunized against gonadotropin-releasing hormone: effect of age at immunization.

Testes function, feedlot performance, and carcass traits were evaluated in bulls actively immunized against gonadotropin-releasing hormone (GnRH) at different ages. Bull calves were randomly assigned to one of seven treatment groups (n = 15 calves/group). Calves were unimmunized (Group 1), immunized at 1.5, 4, 7, or 12 mo of age with a GnRH-keyhole limpet hemocyanin (KLH) conjugate (Groups 2 to 5, respectively), or castrated at 4 mo of age (Groups 6 and 7). Immunized bulls did not receive a secondary, or booster, immunization. Calves in group 6 received Synovex-C at castration and Synovex-S at weaning and feedlot entry. Anti-GnRH titer was evident at slaughter in all immunized bulls. However, the final immune response of bulls immunized at 1.5 mo was significantly lower than the response of bulls immunized at later stages of development. Final scrotal circumference and testis weight in bulls immunized at 4, 7, or 12 mo of age were significantly reduced relative to unimmunized bulls. The final live weight, feedlot gain, and carcass weight of immunized and unimmunized bulls did not differ (P > .05) from the same parameters in steers implanted with Synovex. Longissimus muscle area, marbling score, and backfat thickness did not differ between immunized and unimmunized bulls. The sex class score of the carcasses of immunized bulls did not differ from the score of steer carcasses. In contrast, a significantly higher proportion of carcasses from unimmunized bulls graded as bullock carcasses. Taken together, these data indicate that a single immunization against GnRH at 4 to 12 mo of age results in significant attenuation of testicular growth in bulls. These data also demonstrate that immunization against GnRH reduces the masculinity of carcasses from bulls, but does not affect feedlot performance, longissimus muscle area, marbling score, or backfat thickness. These results suggest that single immunization with the GnRH-KLH conjugate may have practical utility as a noninvasive alternative to surgical castration in management of beef cattle.

Testis function and feedlot performance of bulls actively immunized against gonadotropin-releasing hormone: effect of implants containing progesterone and estradiol benzoate.

The effect of implants containing anabolic steroid (Synovex) on testis function, feedlot performance, and carcass traits was evaluated in bulls, steers, and bulls actively immunized against gonadotropin-releasing hormone (GnRH). Ninety-one Hereford or Hereford x Red Angus bull calves were randomly assigned to a 3 x 2 factorial experiment. The treatments were: 1) unimmunized control (n = 30), 2) actively immunized against GnRH (n = 31), or 3) castrate (n = 30). The classes were 1) unimplanted (n = 45) or 2) implanted (n = 46) with Synovex. Animals in treatment Groups 2 and 3 were either immunized with a GnRH-keyhole limpet hemocyanin (KLH) conjugate or castrated at 3.6 +/- .1 mo of age. Animals assigned to Class 2 received Synovex-C at the time of initial treatment and Synovex-S at weaning and feedlot entry. Animals in treatment Group 2 received a booster immunization at feedlot entry. Anti-GnRH titer was evident at weaning and remained elevated to slaughter in all (31 of 31) immunized animals. Anti-GnRH titer was not evident in steers or unimmunized bulls. Immunization and (or) Synovex decreased (P < .05) serum concentrations of testosterone (T) and scrotal circumference (SC) at weaning. Similarly, SC, testis weight, and tissue concentrations of spermatozoa at slaughter were significantly reduced by immunization, Synovex, or the immunization/Synovex combination. Immunization, but not Synovex, reduced (P < .05) serum levels of T at slaughter. The masculinity of immunized bulls was less (P < .05) than that of control bulls.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of metyrapone to treat pituitary-dependent hyperadrenocorticism in a cat with large cutaneous wounds.

Metyrapone, a drug that inhibits cortisol production, was used to lower plasma cortisol concentration and alleviate skin lesions caused by pituitary-dependent hyper-adrenocorticism in a cat. Plasma cortisol concentration was documented by ACTH stimulation test results. During metyrapone treatment, alopecia, thin skin, and large cutaneous wounds resolved. Metyrapone was administered orally at a dosage of 65 mg/kg of body weight, every 12 hours. Metyrapone may be used in conjunction with surgery in the management of pituitary-dependent hyperadrenocorticism in cats.

Effect on pregnancy rate of nonestrus insemination in previously inseminated dairy cows.

Lactating dairy cows (n = 157) designated for slaughter under the 1986 U.S. Dairy Termination Program were utilized in two trials to determine the effects of a second insemination on fertility. Cows that had been previously inseminated at estrus were inseminated again at 12-24 d later, when not in estrus. Cows that were reinseminated into the uterine body had significantly lower pregnancy rates (4% vs 40.6% for controls). Differences in pregnancy rates when the reinsemination was performed in the mid-cervical region were not significant (34.8% vs 50% for controls). Based upon these studies, intrauterine insemination of cows displaying questionable signs of estrus should be avoided in previously inseminated cows.

Economic modeling of the use of gonadotropin-releasing hormone at insemination to improve fertility in dairy cows.

Economic and sensitivity analysis methods were used to evaluate financial returns from use of gonadotropin-releasing hormone (GnRH) at the time of insemination to enhance fertility of dairy cows. A computer spread sheet was used to determine the best service(s) for GnRH treatment, the increase in conception rate required for economic benefit from treatment, and how profits from GnRH treatment are affected by drug cost, herd reproductive efficiency, and production costs. Financial returns increased from use of GnRH at insemination under most herd conditions. Herds with conception rates less than or equal to 45% benefited from GnRH treatment at any 1 or 2 inseminations. Herds with conception rates greater than or equal to 60% benefited from GnRH treatment only at second or later services. Selection of second and/or third insemination as the GnRH treatment service usually resulted in the greatest total return. The enhancement of fertility necessary to achieve the break-even point with GnRH treatment at third service was 2% for low- and 5% for high-conception-rate herds. Base-line herd conception rates, estrus detection efficiency, replacement costs, value of excess days not pregnant, and cost of treatment had the greatest effect on returns from treatment. Herds with high conception rates and low replacement costs were likely to realize the least benefit from GnRH treatment at insemination. On the basis of our findings, we concluded that GnRH treatment at insemination is a profitable procedure under most herd conditions. Optimal treatment regimens for specific herds may best be determined by using herd performance and management data for calculating returns.

Malignant catarrhal fever in bison.

Malignant catarrhal fever was diagnosed in 3 herds of American bison (Bison bison) in South Dakota from 1973 to 1976. Clinical signs included depression, nasal and ocular discharge, conjunctivitis and keratitis, and diarrhea. Herd morbidity ranged from 3 to 53.8%, and mortality was 100%. At necropsy, ulcerative lesions were found throughout the alimentary tract, trachea, and bronchi. Microscopically, necrotizing vasculitis without thrombosis was found in virtually every organ examined.

Reovirus-like agent associated with neonatal diarrhea in pronghorn antelope.

Reovirus-like particles were demonstrated by negative stain electron microscopic examination of the feces from antelope fawns with diarrhea. Fluorescent antibody tests on frozen sections of ileum from one dead antelope fawn and immunoelectron microscopy tests on feces from two live fawns provided evidence that the antelope agent was serologically related to the neonatal calf diarrhea reovirus-like agent.