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.

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.

Data from two groups of lambs were analyzed. In group one, seasonal patterns of testis growth through 16 mo of age were assessed on 40 spring-born ram lambs (eight Barbados Blackbelly, 10 Suffolk and 22 1/2-Dorset, 1/4-Finnish Landrace, 1/4-Rambouillet). Scrotal circumference (sc) and body weight (wt) were measured at mean ages of 30, 62, 96, 124, 153, 180, 212, 243, 290, 333, 364, 398, 427, 454, 488 and 517 d. A multivariate repeated measures analysis indicated that there were breed differences in ram sc and wt measurements at each age. When logistic growth curves were fit to ram sc data, breed differences were associated with parameters of the logistic curve that defined mature testis size and the period of rapid testis growth. For group two, data were collected on 1,044 lambs from 727 spring lambings over 5 years; 67 sires and 525 dams were represented. Sc and wt were measured in rams at 5 times (mean ages of 44, 63, 97, 129 and 156 d); ewes were weighed at these times and at three additional times (187, 230 and 271 d). All ewe lambs were kept for fall breeding. Fertility, prolificacy and postweaning spring mating behavior of ewes that had lambed were measured. After ewes lambed, they were exposed to vasectomized rams and checked for postweaning spring mating behavior. Restricted maximum likelihood (REML) was used to estimate variance components for additive genetic, ewe, and litter effects in group two Jambs. Heritability estimates for wt at birth to 150 d ranged from .14 to .42. Heritabilities for sc and sc scaled to the 1/3 power of body weight (rsc) ranged from .09 to .57 and from .13 to .55, respectively, and were largest at approximately 90 d. Logistic sc growth curves were fitted to data from individual ram lambs. Heritabilities of the estimated logistic parameters mature sc (A), sc maturing rate (k), age at inflection of the sc growth curve (t₁) and initial 14-d sc (SC14), were estimated at .09±.15, .17±.18, .37±.29 and .40±.14, respectively. Heritability estimates for fertility and spring mating behavior (spbrd) were .04±.13 and .41±.19, respectively. The heritability estimate for prolificacy was zero. Longitudinal additive genetic covariances among wt, sc and rsc at the second, third and fourth measurements were estimated from approximate multivariate REML analysis treating variances as known. Estimated genetic correlations among wts were largest, and ranged from. 77 to .93. Estimated genetic correlations for rsc traits were between .48 and .90. Estimated genetic correlations for sc ranged only from .10 to .67. Pairwise genetic correlations among sc or rsc with fertility or spbrd were estimated to be moderate and positive (.20 and .34, respectively); t₁ had correlations of -.32 and -.48 with fertility and spbrd, respectively. / Ph. D.