B.H. Johnson

Effects of sexual experience, season, and mating stimuli on endocrine concentrations in the adult ram ☆

Two behavioral trials were conducted to determine the endocrine response of cortisol (C), luteinizing hormone (LH), testosterone (T), prolactin (PRL), and growth hormone (GH) in adult rams during exposure to estrous ewes during the breeding and nonbreeding seasons. One-half of the rams in each season were sexually experienced (SE) and the remainder were sexually inexperienced (SI). All SE rams (100%) achieved at least one ejaculation, but only 33% (summer) and 67% (fall) SI rams achieved ejaculation. In the fall, mean C, T, and GH concentrations were elevated (P less than .001) compared to values measured in the summer, whereas LH and PRL levels were higher (P less than .01) in the summer. Overall levels of C, LH, T, and PRL were higher (P less than .05) in SE rams than in SI rams. Mean GH concentration was higher (P less than .10) in SI than in SE rams during restricted and complete access to estrous ewes. In general, LH, PRL, and GH responses were similar during restricted and complete access to females for both SE and SI rams. Cortisol levels were higher (P less than .06) during periods of mating and T levels were higher (P less than .001) during periods where activity was limited to courtship behavior (nasogenital investigation). Correlations of hormones to reproductive behaviors indicated that mounting and intromission were associated with elevations in C and PRL, whereas elevated LH and T tended to be associated with courtship behaviors. Correlations between GH and behaviors were inconsistent. However, there was an increased coincidence between time of female exposure and hormonal response that occurred in the fall; brief exposure to estrous ewes resulted in increases in concentrations of all hormones examined. The most consistent response was observed in sexually experienced rams during restricted access to females during the breeding season. These results provide new information on the effects of season and level of sexual experience upon hormonal and behavioral characteristics of the ram during mating activity.

Effects of consuming endophyte-infected tall fescue on growth, reproduction and lactation in mice selected for high fecundity

Effects of a diet containing endophyte-infected tall fescue seed (83% infected) were investigated using 2 lines of mice, one line selected for fecundity (L(+)) and the other a randomly selected control line (K). Treatments included a commercial stock diet (C), 50% stock plus 50% non-infected tall fescue seed (N), and 50% stock plus 50% infected tall fescue seed (I). The experiment was conducted using mice on respective treatments in 2 phases (successive generations), with 15 to 23 mated females per line and diet subgroups. Mated females of Phase 1 were assigned at random within line to experimental diets which were fed during gestation and through 21 d of lactation. Litters were standardized to 10 pups 1 d after birth. Stock diets were fed to all groups from Day 21 to weaning on Day 28. Weaned male and female pups were allotted to previous diets. Mated females in Phase 2 were managed as in Phase 1 through weaning at 28 d. Diets of males did not affect reproduction and data were pooled within female diets. Selected (L(+)) dams gave birth to more live pups than K dams (P<0.05) during both phases (+3.4 and +2.8 +/- 0.4 pups, respectively). Diet but not line affected littering rate of mated females in Phase 1 (71.3%, I; < 87.1%, C or 93.0%, N; P<0.05) and Phase 2 (82.1%, I < 93.8%, N or 97.1%, C; P<0.05). Diet had no effect on fecundity during Phase 1 but females on I diet had reduced (P<0.05) litter size by 1.9 and 3.2 +/- 0.5 pups compared with the females on N and C diets, respectively, in Phase 2. Feed consumption and weights of dams during lactation generally ranked C>N>I. Growth of pups during both phases also ranked C>N>I. Vaginal opening at 28 d differed by line (71.4%, K < 89.3%, L(+), P<0.05) and diet (56.8%, I < 92.0%, C or 92.2%, N, P<0.05). These results suggest both acute and chronic effects of consumption of endophyte-infected diets. Absence of line-by-diet interactions demonstrates that adverse effects were unrelated to genetic differences between lines.

Effect of oviductal condition on the development of one-cell porcine embryos in mouse or rat oviducts maintained in organ culture

Abstract To determine the effect of varying oviductal conditions on porcine embryo development in mouse oviducts in organ culture, one-cell porcine embryos from each donor female were randomly assigned to the following treatments: medium alone, mouse oviducts obtained from females mated to fertile males or vasectomized males, mouse oviducts from mated fertile females flushed with culture medium, and rat oviducts. Of the embryos cultured in medium alone, 17.3% (n = 52) developed to the morula or blastocyst stage. For porcine embryos cultured in mouse oviducts, 77.1% (n = 35) developed to the morula or blastocyst stage in mouse oviducts obtained from fertile matings; 74.5% (n = 51) in mouse oviducts obtained from females mated to vasectomized males; and 58.7% (n = 46) in flushed mouse oviducts obtained from mated fertile females. Development of porcine embryos in rat oviducts from mated fertile females was limited (17.8% morula or blastocyst; n = 45). Mouse oviducts obtained from females mated to fertile or vasectomized males and not flushed supported one-cell porcine embryo development to a greater extent than flushed mouse oviducts (P 0.90). Cell numbers were similar for embryos reaching the morula or blastocyst stage across all treatments, except for embryos reaching the blastocyst stage in rat oviducts, where cell numbers were significantly lower (P

Active immunization of boars against gonadotrop in releasing hormone. I. Effects on reproductive parameters.

Sexually mature boars were actively immunized against gonadotropin releasing hormone (GnRH) to characterize endocrine and gametogenic changes associated with immunoneutralization of endogenous GnRH. Injections of GnRH conjugated to bovine serum albumin (BSA) given five times over 24 wk induced production of antibodies against GnRH in all animals (n=5). Active immunization against GnRH reduced serum concentrations of testosterone (P<0.05) and luteinizing hormone (LH) (P<0.05), testes volume (P<0.01), paired testis weights (P<0.05), paired epididymis weights (P<0.05), sperm per testis (P<0.01) and seminiferous tubule diameters (P<0.001) when compared with controls (n=4). These results indicate that both steroidogenic and spermatogenic functions are impaired in testes of mature boars actively immunized against GnRH.

Active immunization of boars against gonadotropin releasing hormone. II. Effects on libido and response to testosterone propionate.

Of 20 sexually mature Duroc boars showing normal libido, 10 were actively immunized against gonadotropin releasing hormone (GnRH). After immunization against GnRH, boars showed minimal sexual interest in an estrous female, while untreated boars showed normal libido. Eight of the boars actively immunized against GnRH were randomly assigned to treatment (T) or control (C) groups. Boars in the T and C groups were given testosterone propionate or vehicle, respectively, on Days 0, 5, 10, and 15. Boars in both groups were observed for libido in the presence of an estrous female every 4 d for 28 d. Mean libido score for T boars increased gradually until all boars displayed maximum libido on Day 20, but libido returned to low levels on Day 28. In contrast, C boars remained sexually inactive throughout the study. The results of this study indicate that active immunization of sexually mature boars eliminates sexual behavior and that sexual behavior can be restored quickly by administering testosterone propionate.

Effects of zeranol upon bovine testicular function

Effects of zeranol upon testicular function in bulls were studied. In Experiment I, young bulls (104+/-1.7 days of age) were either implanted with 36 mg zeranol or served as controls with reimplantation on days 56 and 112 after first implant. After a 168-day treatment period, half the bulls were orchidectomized with the remaining bulls assigned to a 168-day recovery period, after which they were also orchidectomized. Zeranol inhibited testicular development during the treatment period. Testosterone (T) concentrations were lower (P<0.01) in treated bulls. Spermatozoa were absent in testes of treated bulls while control bulls averaged 27x10(6) sperm per gram of testis. At the end of the 168-day recovery period, testes weights and sperm concentrations were similar (P>0.10) between bulls previously treated with zeranol and controls. Implantation of older bulls with either 36 mg (267+/-3.4 days of age: Experiment II) or 72 mg (16 months of age: Experiment III) of zeranol had no effect (P>0.10) upon spermatogenesis or T production over a 168-day treatment period. The results indicate that the inhibitory effects of zeranol upon bovine testicular function are age-dependent and suggest that there may be an increased sensitivity of the hypothalmic-pituitary-testicular axis to zeranol in the prepuberal bull.

SURVIVAL OF EARLY PREIMPLANTATION PORCINE EMBRYOS AFTER CO-CULTURE WITH CELLS PRODUCING AN AVIAN RETROVIRUS

To determine the relative survival of porcine embryos after co-culture with cells producing an avian retrovirus, four-cell stage embryos were obtained from sows following synchronization with altrenogest and superovulation with gonadotropins. These embryos were randomly assigned to the following treatments: no manipulation (zona-intact); zona removed with acidified Tyrodes solution (zona-free); and zona removed followed by co-culture with D-17 canine cells producing an avian retrovirus vector derived from spleen necrosis virus (zona-free + co-culture). The survival rates of four-cell stage embryos to morulae or early blastocysts during a 48-h culture period were 93.3, 80.0 and 57.7% in zona-intact, zona-free and zona-free + co-culture groups, respectively. Following embryo transfer, the development of embryos to fetuses at six weeks of gestation was 37.5, 30.0 and 11.7% in zona-intact, zona-free and zona-free + co-culture groups. These results indicate that early preimplantation porcine embryos can develop to apparently normal fetuses following co-culture with cells producing a retrovirus, and the feasibility of this method for retrovirus-mediated gene transfer in pigs was demonstrated.

Effects of pretreatment with adrenocorticotropin on endocrine and behavioral responses of bulls to sexual activity

Peripheral concentrations of cortisol, growth hormone and testosterone were determined in two experiments which examined the endocrine and behavioral responses of sexually mature Angus bulls to an estrous female (Experiment 1) and to female exposure 5 hours following an adrenocorticotropin (ACTH) injection (Experiment 2). Sexual activity of bulls in Experiment 1 significantly increased levels of cortisol when compared with concentrations before exposure to a female. Administration of ACTH in Experiment 2 consistently elevated levels of cortisol by 30-fold (P<0.01) when compared with pre-ACTH concentrations. This heightened level of cortisol persisted throughout the period of exposure to an estrous cow, although a gradual decline in cortisol concentrations occurred over time (P<0.05). In Experiment 1, growth hormone profiles tended to increase in response to sexual activity (P<0.10), whereas in Experiment 2, growth hormone increased in response to ACTH administration (P<0.01) and to female exposure (P<0.01). Concentrations of testosterone were unaffected (P>0.10) by mating activity in Experiment 1. In Experiment 2, acute suppression (P<0.01) in testosterone concentrations 5 hours after ACTH administration coincided with the exposure period to the estrous female. Frequencies of mounting behavious (penis extension, mounting, intromission and ejaculation) exhibited by ACTH-treated bulls were significantly lower compared with the frequencies two days earlier. Exogenous ACTH administration suppressed reproductive behaviors of bulls and altered secretion of cortisol, growth hormone and testosterone. Furthermore, these data provide evidence that specific mating behaviors of the bull can be influenced by circulating steroids.

Developmental potential of day 13 porcine embryonic disk under in vitro culture conditions

SummaryEmbryonic disks were microsurgically isolated from adjacent trophoblast tissue, and cultured for varying periods in vitro. During the first 24 h of culture, vesicles (1 to 4/disk) composed of mesoderm and endoderm formed from the ventral surface. In the subsequent culture period, the vesicles continued to increase in size and by 96 h in vitro, most originally multivesiculated explants possessed a single vesicle formed by delamination and coalescence of smaller vesicles. Scanning electron microscopy revealed the formation of grooves and ridges in abnormal attempts at differentiation by the embryonic ectoderm. Endoderm comprising the outer tissue layer of the vesicle underwent a gradual alteration in surface morphology during in vitro culture. Initially flat, with a paucity of microvilli, these cells became dome-shaped with an abundance of microvilli. In addition, they became highly secretory as revealed by the presence of numerous secretory droplets at their surface. After culture for periods of up to 10 d, several explants displayed areas containing pulsating tissue, with contractions occurring at a rate of 20 to 30/minute, indicative of mesoderm differentiation. Culture of porcine isolated embryonic disk in vitro should enhance investigations into the regulation of germ, layer formation and differentiation and assist in determining the tissue source of conceptus secretory products.

Production of transgenic mice following deoxyribonucleic acid microinjection and embryo freezing

Experiments with mouse embryos were designed to assess the feasibility of freezing embryos after DNA microinjection. One-cell pronuclear stage mouse embryos were microinjected with cloned deoxyribonucleic acid (DNA) and cultured in vitro to the late eight-cell stage. Microinjected and matched control embryos were frozen and stored in liquid nitrogen. Following thawing, embryos were cultured for 8 h and transferred to recipient females. In a separate set of experiments, embryos were transferred to recipients immediately following DNA microinjection. Control (uninjected) embryos developed to the late eight-cell stage significantly better than surviving microinjected embryos. Of the embryos thawed, 76% of the microinjected and 60% of the control embryos survived to be transferred to recipients. Progeny were obtained with similar survival rates from both groups following embryo transfer with transgenic mice identified among the progeny from microinjected embryos. Mouse embryos can be microinjected with DNA, cultured in vitro, frozen, thawed, transferred to recipients and transgenic progeny can be obtained.