No description available.

No description available.

Includes bibliographical references (leaves 274-316) Examines several aspects of male reproduction in the sheep, and how these are related to fertility in the female when semen is introduced by natural mating or artificial insemination.

Includes bibliographical references (leaves 191-207) / xiv, 207 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Examines the interactions between thyroid hormones and male reproductive function in mature, prepubertal and post pubertal Merino rams. Hypothyroidism or hyperthyroidism was induced in these rams for 8-10 weeks and their reprodroductive endocrine axis and testis functions were assessed. / Thesis (Ph.D.)--University of Adelaide, Dept. of Animal Sciences, 1986

Includes bibliographical references (leaves 274-316) / xxii, 333 leaves : ill. (chiefly col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Examines several aspects of male reproduction in the sheep, and how these are related to fertility in the female when semen is introduced by natural mating or artificial insemination. / Thesis (Ph.D.)--University of Adelaide, Dept. of Animal Sciences, 1991

Spring-born ram lambs were used to examine: (1) sexual maturational changes in LH, FSH and prolactin (PRL) secretion, testicular gonadotropin receptors, and testicular size and function; (2) predictability of yearling ram reproductive function from juvenile testicular size and reproductive hormone measurements. Despite continuous increases in testis size, serum LH-profile characteristics became greatest between 2 and 4 months and declined thereafter. However, LH-peak frequency increased by about 2-fold between 6 and 7 months; this was associated with marked increases in testosterone (T) secretion and spermatogenic function. Mean FSH and PRL levels were maximum at 2 months and 3 to 5 months, respectively, and decreased thereafter. Increases in steroidogenic and spermatogenic function were due partly to increases in testicular content of LH and FSH receptors. Yearling ram testis size and spermatogenic function were predictable from testis size at 5 to 6 months, neonatal (50 days) secretion of LH and T, and pubertal (150 days) secretion of T. However, combinations of testicular size and reproductive hormone measurements provided greater predictive power.

During the nonbreeding season (July), three groups of five Dorset x Leicester x Suffolk rams were assessed over a period of 5 days. One group of rams (control) was implanted (sc) with five 5cm empty Silastic capsules (i.d. 3.4mm, o.d. 4.6mm); two other groups, designated as Low-E$ sb2$ and High-E$ sb2$, received five estradiol filled capsules of either 5cm or 10cm, respectively for 4 days. Estradiol treatment elevated serum estradiol concentration about 150% in the Low-E$ sb2$ groups (15.7 $ pm$ 1.3 pg/ml) and 300% in the High-E$ sb2$ groups (26.6 $ pm$ 2.4 pg/ml) compared with controls (6.3 $ pm$ 0.8 pg/ml). In the absence of LH pulsing, mean LH, FSH and testosterone concentrations were all decreased significantly (P $<$.05) with increasing estradiol concentration, while PRL concentration was increased (P $<$.05) by as much as 105%. In the LH-pulsed groups, LH-peak height on day 4 was comparable for all three groups of rams and peak frequency was, as expected, consistently increased to 4 peaks per 6 hours. The increase in mean testosterone concentration (P $<$.05) in all three groups was due to an increase in testosterone baseline concentration and testosterone peak frequency.

No description available.

Reproductive performance of Dorset ewes in the Cornell University STAR accelerated lambing program was evaluated. This program consists of five 30-d concurrent breeding and lambing periods per year beginning on January 1 (Sl), March 15 (S2), May 27 (S3), August 8 (S4) and October 20 (S5). Optimally, a ewe could lamb every 7.2 mo beginning at 1 yr of age, Records on 1,084 ewes over 7 yr beginning S1, 1982 Reproductive traits considered were ewe fertility, prolificacy, days to first lambing (DFL) and days between lambing (DBL). Fertility and prolificacy differed (P < .001) by exposure seasons. Exposure during favorable seasons (S1, S4, S5) increased fertility (P < .001) and prolificacy (P < .01) over that observed in unfavorable seasons (S2, S3). On average, first lambing occurred at 476 ± 5 d with ewe lambs first exposed during S1, S4 and S5 lambing at younger ages (P < .001). Ewes had more DBL (P < .001) if initial exposure following lambing occurred during an unfavorable season. A curvilinear relationship of ewe age with fertility (P < .001) , prolificacy (P < .01) and DBL (P < .05) was observed in ewes less than 4 yr old. At first exposure following lambing, fertility was lower (P < .001) than at subsequent exposures and ewes that had nursed lambs were less prolific (P < .01) than those that had not. Prolificacy and nursing status had little effect on fertility or DBL (P > .10). Fertility was transformed to an underlying liability scale based on the expected fertility of ewes of a given age and reproductive history. Variance components were estimated by least-squares (LS) and restricted maximum likelihood (REML) procedures. First-exposure fertility was not heritable. heritabilities for fertility at first post-lambing exposure, first-lambing prolificacy, and second-lambing prolificacy were .191 ± .088 (LS) and .200 ± .132 (REML), .914 ± .091 (LS) and .158 ± .144 (REML), and .168 ± .082 (LS) and .210 ± .137 (REML), respectively. Genetic variation in DFL (P < .01) and DBL (P < .001) was found. Although intrasire ewe variation was detected for prolificacy (P < .001) and DBL (P < .01), repeatability estimates were low and smaller than heritability. / Ph. D.

Maintenance of pregnancy in the ewe depends on progesterone synthesized by the ovaries during the first third of gestation and by the placenta during the last two-thirds of gestation. There have been few investigations of in vitro synthesis of progesterone by the ovine placenta or of mechanisms controlling placental steroidogenesis. Weekly blood samples were collected from ten gestating ewes that were sacrificed for collection of placental tissue on either day 80 (n=5) or day 115 (n=5) of gestation. All blood samples were analyzed for progesterone by radioimmunoassay. Immediately after each ewe was sacrificed, cotyledons were collected from different areas of each placenta, minced, and incubated in 2 ml of culture medium for either .5, 1, or 2 h. Minced tissue (100 mg) was incubated either in the presence or absence of pregnenolone and the tissue was subject to addition of either human Chorionic Gonadotropin (hCG), 3’, 5', cyclic adenosine monophosphate (cAMP), luteinizing hormone-releasing hormone (LHRH) or no additional treatment. Progesterone concentration in the medium after incubation were determined by radioimmunoassay. The temporal pattern of in vivo progesterone synthesized during gestation exhibited a biphasic increase with elevations occurring between days 70 and 80, and 95 and 115 of gestation. The difference in progesterone concentration in incubation medium after incubation of placental tissue collected on day 80 or day 115 of gestation was similar in magnitude to the difference in plasma progesterone concentrations of samples collected on those days. At day 80 and 115 of gestation, in vitro progesterone concentrations were 8.4 and 15.3 ng/ml, respectively, while in vivo progesterone concentrations at day 80 and 115 were 7.2 and 12.5 ng/ml, respectively. Progesterone accumulation in the medium of placental tissue collected at 115 days of gestation was greater than concentrations of progesterone in tissue collected at 80 days of gestation (P<.01). HCG had no effect on progesterone accumulation in the incubation medium; however, cAMP and LHRH significantly affected progesterone concentrations when pregnenolone was added to the medium of tissue collected on day 115. Cyclic AMP significantly increased progesterone concentrations in the medium after 2 h of incubation over that of tissue incubated alone (354.1 vs 402.6 ng/g). Mean progesterone concentrations in the medium of tissue incubated with LHRH were lower than control incubations after 1 h (288.8 vs 355.6 ng/g) and 2 h (306.1 vs 354.1 ng/g) of incubation. / M.S.