Breed differences in clearance of porcine FSH in hypophysectomized rats.

Extracts of anterior pituitary (AP) glands were infused i.v. into hypophysectomized male rats followed by sequential sampling of blood for 120 min. Determination of follicle-stimulating hormone (FSH) concentrations established that FSH from Chinese Meishan males decreased in the circulation of rats more slowly than FSH in extracts of AP from crossbred occidental pigs (P<0.003). Additionally, FSH from AP extracts of castrated males disappeared somewhat more slowly (P<0.06) than FSH from extracts of boars. Evaluation of FSH by bioassay and radioimmunoassay yielded similar concentrations in AP from Meishan and crossbred boars. Serum testosterone concentrations increased with time through 90 min after infusion of AP, but the rate of increase of testosterone was not related to amount of luteinizing hormone (LH) that was administered indicating LH receptor saturation. Unexpectedly, the rate of increase in testosterone was more rapid with AP extracts from boars than with extracts from castrated males. Observations from the current study imply structural alterations of FSH in the AP of Meishan males relative to crossbred males allowing sustained concentrations in the circulation, and this FSH possesses similar activation of the FSH receptor. The amount of LH in the AP extracts saturated the LH receptors of the hypophysectomized male rats, but some factor in extracts of boars differed from those of castrated males.

Identification of genomic regions controlling plasma FSH concentrations in Meishan-White Composite boars.

The Chinese Meishan (ME) breed of pig is unique for many reproductive traits. Compared with Western breeds of swine, ME females reach puberty earlier, ovulate more ova per estrus, and have greater uterine capacity, while intact males (boars) have smaller testes and extremely elevated plasma levels of pituitary-derived glycoprotein hormones. In an effort to identify the genetic mechanisms controlling the elevated plasma levels of pituitary-derived glycoprotein hormones [in particular, follicle-stimulating hormone (FSH)] and to determine whether some of these genetic factors are also responsible for differences in other phenotypes, we scanned the entire genome for regions that affected plasma FSH in boars from a Meishan-White Composite (equal contributions of Chester White, Landrace, Large White, and Yorkshire) resource population. Initially, the entire genome of 121 boars was scanned for regions that potentially influenced plasma FSH. The most significant genomic regions were further studied in a total of 436 boars. Three genomic regions located on chromosomes 3, 10, and X apparently possess genes that significantly affect FSH level, and one region provided suggestive evidence for the presence of FSH-controlling genes located on chromosome 8. The region on the X chromosome also affected testes size. Similar genomic regions to those identified on chromosomes 3, 8, and 10 in this study have been identified to affect ovulation rate in female litter mates, supporting the hypothesis that plasma FSH in pubertal boars and ovulation rate in females is controlled by a similar set of genes.

Endocrine and molecular influences on testicular development in Meishan and White Composite boars.

The aim of this study was to evaluate developmental changes in thyroid hormone and other key endocrine hormones/molecular markers produced by testicular cells, in relation to breed differences in proliferation and maturation of Sertoli cells and general testicular morphological development in Meishan (MS) and White Composite (WC) boars. Blood samples and testes were collected on days 60, 75, 90 and 105 post coitum (dpc) and days 1, 7, 14 and 25 post partum (dpp). Testes were immunostained for thyroid hormone receptor-beta1 (THRbeta1), GATA4, Müllerian-inhibiting substance (MIS), 17-alpha-hydroxylase (P450(c17)) and inhibin subunits (alpha, betaA, betaB). In addition, protein levels were determined by densitometry. Plasma concentrations of free triiodothyronine (T(3)) were greater in MS (hyperthyroid) compared with WC (hypothyroid) boars (P<0.01) during fetal life, but the reverse was evident postnatally. Elevated levels of free T(3) during fetal life were associated with increased levels of THRbeta1, suggesting increased thyroid responsiveness of the testis during this time, contrasting with observations during early postnatal life. Localization patterns of THRbeta1, MIS, GATA4 and the inhibin subunits were consistent with previous studies. MIS protein levels declined more rapidly (P<0.001) in MS compared with WC Sertoli cells postnatally, consistent with earlier maturation of Sertoli cells as indicated by our previous study. In this study, transient neonatal hyperthyroidism in MS boars during late gestation was associated with a decline in proliferation and early maturation of Sertoli cells, followed by early onset of puberty in this breed. These observations indicate a possible role for thyroid hormone in the modification of Sertoli cell development, thereby influencing growth and differentiation of the testis in pigs.

Expression levels of Mullerian-inhibiting substance, GATA4 and 17alpha-hydroxylase/17,20-lyase cytochrome P450 during embryonic gonadal development in two diverse breeds of swine.

Sexual differentiation and early embryonic/fetal gonad development is a tightly regulated process controlled by numerous endocrine and molecular signals. These signals ensure appropriate structural organization and subsequent development of gonads and accessory organs. Substantial differences exist in adult reproductive characteristics in Meishan (MS) and White Composite (WC) pig breeds. This study compared the timing of embryonic sexual differentiation in MS and WC pigs. Embryos/fetuses were evaluated on 26, 28, 30, 35, 40 and 50 days postcoitum (dpc). Gonadal differentiation was based on morphological criteria and on localization of GATA4, Mullerian-inhibiting substance (MIS) and 17alpha-hydroxylase/17,20-lyase cytochrome P450 (P450(c17)). The timing of testicular cord formation and functional differentiation of Sertoli and Leydig cells were similar between breeds. Levels of GATA4, MIS and P450(c17) proteins increased with advancing gestation, with greater levels of MIS and P450(c17) in testes of MS compared with WC embryos. Organization of ovarian medullary cords and formation of egg nests was evident at similar ages in both breeds; however, a greater number of MS compared with WC embryos exhibited signs of ovarian differentiation at 30 dpc. In summary, despite breed differences in MIS and P450(c17) levels in the testis, which may be related to Sertoli and Leydig cell function, the timing of testicular differentiation did not differ between breeds and is unlikely to impact reproductive performance in adult boars. In contrast, female MS embryos exhibited advanced ovarian differentiation compared with WC embryos which may be related to the earlier reproductive maturity observed in this breed.

Stereological evaluation of Sertoli cell ontogeny during fetal and neonatal life in two diverse breeds of swine.

Chinese Meishan (MS) boars have smaller testes due to fewer Sertoli cells compared with White Composite (WC) boars. The objective was to describe Sertoli cell development relative to circulating FSH concentrations in fetal and neonatal MS and WC boars. Testes and blood samples were collected on days 60, 75, 90 and 105 postcoitum (dpc) and 1, 7, 14 and 25 postpartum (dpp). One testis was immunostained for GATA4 or Ki67 antigen to evaluate total and proliferating Sertoli cell numbers respectively. Testicular size was greater (P<0.01) in WC than MS boars at all ages, associated with a greater mass of interstitial tIssue. Tubular mass (P<0.01) was greater in prenatal WC boars, but postnatally increased more rapidly (P<0.001) in MS boars, exceeding WC boars by 25 dpp. Sertoli cell numbers increased with age, was greater (P<0.001) in WC than MS boars during prenatal development but increased rapidly (P<0.01) by 1 dpp in MS and thereafter was similar in both breeds. The proportion of Ki67-positive Sertoli cells was maximal at 90 dpc, declining thereafter, did not differ between breeds through 7 dpp, but was greater (P<0.05) in WC than MS boars at 14 and 25 dpp. Plasma FSH concentrations were greater (P<0.05) in WC than MS boars at 75 dpc. FSH concentrations were elevated at 105 dpc (MS) and 1 dpp (WC) but declined thereafter with advancing postnatal age in both breeds. This study illustrates that late gestation represents the period of maximal Sertoli cell proliferation. Despite asynchronous Sertoli cell population growth between breeds during early postnatal life, differential mature Sertoli cell numbers and testicular size are probably due to differences in duration of the proliferative period after 25 dpp, potentially regulated by Sertoli cell maturation and blood-testis barrier formation. These events were not associated with fetal or early postnatal changes in FSH secretion.

Quantitation of deoxycorticosterone and its relationship to progesterone in the prepartum bovine.

A method and its validation is described for the radioimmunological measurement of deoxycorticosterone (DOC) in bovine serum. Levels of DOC and progesterone were determined in six pregnant heifers from one to three weeks before and during parturition. Levels of these steroids fluctuated widely from day to day and tended to be inversely related (r = -0.24). High levels of DOC in conjunction with low levels of progesterone at or near parturition are suggestive that DOC is involved in the parturition process.

Effect of ovarian regression and molt on plasma concentrations of thymosin beta 4 in domestic hens (Gallus domesticus).

Molt induced by infusion of a gonadotropin-releasing hormone agonist (GnRH-A, ([D-leu6,Pro9]-GnRH N-ethylamide]) or feed withdrawal (FW) has been used as a model to study interactions between ovarian activity and thymosin beta 4 during molting in domestic hens. Thirty-three laying hens were divided into three groups: 1, controls, 2, GnRH-A infusion induced molt (GnRH-A), or 3, FW induced molt. All groups had reduced daylength. Blood was sampled weekly and assayed for concentrations of thymosin beta 4 and progesterone (P4). Plasma P4 concentrations were significantly depressed in both treatment groups compared to controls, indicating ovarian regression. Plasma P4 concentrations had returned to control values in the GnRH-A group by 28 d after the start of treatment, while P4 was still depressed in the FW group at day 42 when the experiment ended. Plasma concentrations of thymosin beta 4 were elevated relative to controls from day 7 through day 14 in the GnRH-A group and from day 7 until day 28 in the FW group. It is concluded that plasma concentrations of thymosin beta 4 are elevated during molting in domestic hens, but the elevation is not attributable to depressed P4 concentrations.

Characterization of secretion of thymosin alpha 1 and thymosin beta 4 during prepuberty, estrus and pregnancy in the bovine female.

The objective of the present study was to characterize secretion of thymosin alpha 1 (A1) and thymosin beta 4 (B4) during different stages of ovarian function and pregnancy in bovine females. One hundred and thirty-five prepubertal heifers averaging 9 mo of age at the time the study was initiated were used. Estrous detection was conducted twice daily using intact bulls fitted with marking harnesses. Blood samples were collected at first behavioral estrus and at the time of rectal palpation for pregnancy. Heifers were weighed at the beginning of the study and every 56 days and additional blood samples were collected at those times. Plasma was harvested and radioimmunoassays were conducted to quantify concentrations of thymosin A1 and B4. Mean concentrations of thymosin A1 and thymosin B4 were determined during prepuberty, estrus during which conception did not occur, estrus during which conception did occur, pregnancy and in heifers that failed to attain puberty. Mean plasma concentrations of thymosin A1 and B4 were greater at estrus during which conception occurred than at any other period (P less than .01). Regressions of days prepubertal and days post conception on thymosin A1 and B4 were analyzed. During the 100 days prior to puberty, thymosin A1 and B4 did not change in the heifers that ultimately conceived. However, in the heifers that were never determined to be pregnant by rectal palpation, concentrations of both thymosin A1 and B4 increased linearly during prepuberty (P less than .01). A decline in thymosin A1 and B4 concentrations occurred in a quadratic fashion from conception through the first 100 d of pregnancy (P less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Artificial insemination of subtropical commercial beef cattle following synchronization with cloprostenol (ICI 80996): I. Fertility.

Two trials were conducted over a two-year period with 519 cycling Bos taurus x Bos indicus heifers and cows. The objectives of these trials were: 1) To compare fertility of artificial insemination at the cloprostenol-induced estrus and the naturally occurring estrus, 2) To evaluate the fertility of artificial insemination at a predetermined time (Timed AI) following an estrous synchronization regime with cloprostenol (CLP) and 3) To define the optimum interval from a second CLP treatment for Timed AI. In Trial I, 128 animals were assigned to four treatments: 1) Controls, which were inseminated at the natural occurring estrus; 2) timed AI at 72 hr and again at 96 hr post-second CLP; 3) Timed AI at 72 hr post-second CLP and 4) AI at the CLP-induced estrus. Trial II included 391 heifers distributed among six treatments; 1) Timed AI between 70 and 90 hr post-second CLP; 2) Sham AI between 70 and 90 hr post-second CLP, 3) Chute Stress between 70 and 90 hr post-second CLP; 4) AI at the CLP-induced estrus; 5) Control-AI at the naturally occurring estrus and 6) Non-treated and exposed to fertile bulls. The fertility of the animals artificially inseminated at the CLP-induced estrus was similar to that of insemination at the naturally occurring estrus in Trial I and Trial II (30 vs 46%; 37 vs 38%, respectively). The first service pregnancy rates of the animals bred at a predetermined time were similar to those bred at the CLP-induced estrus in Trial I, but lower in Trial II (P<.01).

Superovulation and embryo quality in beef cows using PMSG and a monoclonal anti-PMSG.

The long half-life of pregnant mare serum gonadotrophin (PMSG) reduces its application in the superovulation of cattle; thus, a monoclonal antibody to PMSG (anti-PMSG) was administered at the onset of estrus to increase the number of transferable embryos. Angus, Hereford and Angus x Hereford cows (n = 149) 3 to 9 yr old were assigned randomly to one of three dosages of PMSG (1500, 3000 or 6000 IU) with or without an equivalent dosage of anti-PMSG. Embryos were collected nonsurgically on Day 8 (estrus = Day 0), and all cows were ovariectomized on Day 9. The percentage of cows exhibiting estrus and ovulating decreased (P<0.05) with an increasing dosage of PMSG (82, 76 and 44% for 1500, 3000 and 6000 IU, respectively). Ovarian and total corpora lutea (CL) weight increased (P<0.001) linearly as PMSG dosage increased, but were reduced (P<0.001) curvilinearly by anti-PMSG, resulting in a PMSG by anti-PMSG interaction (P<0.001); the interaction was also significant (P<0.05) for ovulation rate (14.0 vs 14.3, 21.5 vs 24.4 and 29.2 vs 6.6 CL for 1500, 3000 and 6000 IU PMSG, without vs with anti-PMSG, respectively). Anti-PMSG increased (P<0.001) the number of small ovarian follicles (1 to 3 mm diameter) and decreased (P<0.001) the number of large follicles (>10 mm) at ovariectomy; the number of large follicles increased (P<0.001) with PMSG dosage. The number of total and transferable embryos recovered did not differ among PMSG and anti-PMSG dosages; however, the percentage of transferable embryos decreased (P<0.01) with increasing PMSG dosage. In general, neither PMSG dosage nor anti-PMSG influenced embryo quality.

Relationship of fetal position within the uterus to fetal weight, placental weight, testosterone, estrogens, and thymosin beta 4 concentrations at 70 and 104 days of gestation in swine.

Fetal intrauterine position relative to the sex of adjacent fetuses has an effect on reproductive performance in rodents. An experiment was conducted to determine whether sex of adjacent fetuses in utero has an influence on fetal and placental weights and whether the hormonal mechanisms documented in rodents are similar in fetal pigs. Sows were slaughtered at 70.1 +/- 1.7 d (n = 123) and 104.5 +/- .05 d (n = 135) of gestation. The fetuses and placentas were removed from the uterus and the position and sex of each fetus was recorded to indicate whether the fetus was between two males, two females, or a male and a female. Fetal blood was sampled for later hormonal analysis. At 70 d of gestation, male fetal and placental weights were heavier than those of females (P less than .05), but no differences were detected relative to the sex of adjacent fetuses. At 104 d of gestation, a fetus surrounded on each side in utero by fetuses of the opposite sex (two males or two females) was lighter in weight than a fetus surrounded by fetuses of the same sex (P less than .01). Differences in fetal weight due to the sex of adjacent fetuses were not related to placental function because placental weights were generally not different at 104 d of gestation. By 104 d of gestation, most placentas were not separated by necrotic regions and were in close apposition with surrounding placentas. No differences in growth or development could be related to hormonal effects (testosterone, estrone, or estrone sulfate) from surrounding fetuses.(ABSTRACT TRUNCATED AT 250 WORDS)

Lack of an association between plasma follicle-stimulating hormone concentrations and ovarian weight in prepubertal gilts.

Selection for increased number of corpora lutea in gilts is associated with increased plasma FSH concentrations during pubertal development. In the current study, 270 gilts from a control (CO) line and a line selected for increased ovulation rate (OR) were unilaterally ovariectomized at 85 d of age, and this ovarian weight was related to FSH concentrations at 65, 75, and 85 d of age. Gilts were produced during two farrowing seasons, spring and fall, and the age at first estrus was monitored from 160 to 250 d. Plasma FSH was greater in OR than in CO gilts at 65 (P < 0.01) and 75 d (difference in spring greater than in fall, P < 0.01), but FSH at these ages was not correlated with ovarian weight at 85 d. At 85 d, FSH did not differ in gilts of these lines; however, FSH was negatively correlated (r = -0.27, P < 0.01) with ovarian weight. The proportion of gilts detected in estrus was less for spring-born CO gilts than for spring-born OR or for fall-born CO and OR gilts (78 vs. 92%, season x line, P < 0.02). The age at first estrus was similar in the two lines but was earlier (P < 0.01) for spring-born than for fall-born gilts (194 vs. 204 d). Concentrations of FSH at each of the ages examined were not correlated with the age at first estrus. These observations support the conclusion that selection for a greater number of corpora lutea produces a correlated increase in plasma FSH during early pubertal development. This increase in FSH most likely reflects differences in FSH synthesis and release and not differences in the stage of pubertal development.

Negative relationship between blood concentrations of follicle-stimulating hormone and testicular size in mature boars.

Relationships between blood concentration of FSH and testicular size and daily sperm production were evaluated with data obtained from five studies originally designed to investigate regulation of FSH secretion in Meishan (MS), White composite (WC), and crossbreds of these. A minimum of three blood samples/boar were obtained at greater than 4-d intervals for determination of FSH, and testes were obtained at castration or slaughter. In a random sample of boars, FSH was fivefold greater (P < .01) in MS than in WC boars (n = 22/group). Daily sperm production (DSP)/gram of testis (estimated by counting elongated spermatid nuclei in testicular homogenates) was similar in the groups, but testicular weight (TWT), adjusted for body weight, was less (P < .01) in MS than in WC, yielding lower total daily sperm production (TDSP; P < .05) in MS boars. In four populations (one with MS, one with WC, and two with crossbreds; n = 34 males), boars were selected for extremes in FSH concentrations from larger groups. Across all populations, a threefold greater plasma FSH concentration was associated with a 32% smaller TWT (P < .01). Coincident with increased FSH, TDSP was 33% less (P < .05). In 48 MS x WC boars that were selected for divergence in plasma FSH during pubertal development (4 to 6 mo of age), this divergence was retained at 1 yr (P < .01). Retrospectively, the divergence in FSH was also apparent at 2 and 8 wk of age (P < .05), and the boars with elevated FSH had smaller testicles, lower DSP, and lower TDSP (P < .01). These studies document a negative relationship in mature boars between FSH secretion and testicular size accompanied with decreased TDSP.

Ovarian responses to intramuscular or intravenous administration of prostaglandin F2 alpha in control and FSH-treated beef heifers.

Sixty Simmental crossbred heifers 18 to 20 mo of age were detected in estrus and assigned at random to a 2 x 2 factorial design study with 30 controls, and 30 given FSH. Half of each group was given prostaglandin F2 alpha (PGF) i.v. and the rest i.m. Injections of follicle-stimulating hormone were started on d 7 to 14 of an estrous cycle and continued for 5 d or until ovariectomy; PGF was administered either i.v. or i.m. at 48 (25 mg) and 60 (15 mg) h after the initial FSH injection. Control females received a similar PGF treatment on a day between d 9 and 15 of the estrous cycle. Blood samples were collected from all animals immediately before PGF administration and every 12 h thereafter until ovariectomy. Within each of the four experimental subgroups, ovariectomies were performed at either 24, 48 or 72 h (five/time group) after initial PGF injection. Ovarian and corpus luteum (CL) weights were recorded as well as number and size of follicles and number of ovulations. Regression of the CL was slower (P less than .05) after administration of PGF i.v. than i.m. (CL weight was 2.6 vs 3.3 +/- .2 g for i.m. and i.v. groups, respectively). Exogenous FSH increased estradiol-17 beta (E2) concentrations, and FSH-treated heifers had more (P less than .05) early ovulations than control heifers did. Ovulations in FSH-treated heifers had begun to occur by 24 h after i.v. and i.m. PGF injection.(ABSTRACT TRUNCATED AT 250 WORDS)

Overexpression of beta-subunit of thyroid-stimulating hormone in Meishan swine identified by differential display.

Anterior pituitary gland RNA isolated from Meishan (MS) and White Composite (WC) sexually mature boars was compared by a newly developed method of differential expression cloning called differential display. A number of cDNAs were identified that differed distinctly in expression between these breeds. The gene for beta-subunit of thyroid-stimulating hormone (TSH-beta) was initially identified as more highly expressed in MS than in WC boars. Subsequently, RNase protection assays and TSH RIA were used to quantify the magnitude of differences in transcription and translation in both males and females. Mature MS pigs had threefold greater expression of TSH-beta (P < .05) and greater plasma TSH concentrations than mature WC pigs (P < .01). The cDNA cloning and sequence analyses indicate identity in TSH-beta mRNA between MS and WC males. Elevated plasma TSH concentration may contribute MS pigs reaching sexual maturity earlier than WC or other European breeds. The method used in this study provides a useful molecular tool 1) to detect differentially expressed genes, 2) to study genetic variation that occurs at the transcription level between individuals, populations, or breeds; and additionally, 3) to identify candidate genes that control economically important quantitative traits in livestock.

Increased plasma follicle-stimulating hormone concentrations in prepubertal gilts from lines selected for increased number of corpora lutea.

Plasma follicle-stimulating hormone (FSH) was evaluated in gilts from two studies in which ovulation rate was increased through direct selection for number of corpora lutea (CL) to determine whether selection for ovulation rate affected FSH secretion during prepubertal development. In the first study, 76 control and 110 selected gilts of University of Nebraska gene pool lines were bled twice during prepubertal development. Plasma FSH concentrations were greater (P < 0.05) at 53 (13.5%) and 75 (21.3%) d of age in selected than in control gilts. In the second study, 254 control gilts, 261 gilts from a line selected for ovulation rate, and 256 gilts from a line selected for uterine capacity were bled at three prepubertal ages. Plasma FSH was greater (P < 0.05), relative to controls, on d 34 (> 24%), 55 (> 13%), and 85 (> 10%) in White Composite gilts selected for either increased ovulation rate or for greater uterine capacity. Unilateral ovariectomy and hysterectomy were performed at 160 d of age on random gilts in these three lines (n = 377); weights of these organs were evaluated to determine whether selection affected their development. Ovarian and uterine weights were less (P < 0.01) in the control than in the ovulation rate line. Subsequently, ovulation rate was determined during pregnancy (n > or = 130 gilts/line). Controls had fewer (P < 0.01) CL (14.6) than gilts of the ovulation rate line (17.7) but numbers similar (P > 0.10) to those of gilts of the uterine capacity line (14.7). Within each line, plasma FSH only on d 85 correlated positively with subsequent ovulation rate (P < 0.03, 0.001, and 0.08; r = 0.17, 0.30, and 0.15 for control, ovulation rate, and uterine capacity lines, respectively). Ovarian weight at 160 d of age also correlated with subsequent ovulation rate (P < 0.03 and 0.001; r = 0.23 and 0.38) in control and ovulation rate gilts but not in uterine capacity gilts (P > 0.10; r = 0.11). Gilts selected for increased number of CL, in two independent studies, had greater concentrations of FSH during prepubertal development than respective controls. The modest but significant, positive association of FSH at 85 d of age with subsequent ovulation rate provides additional support for using plasma FSH in prepubertal gilts to indirectly select for ovulation rate.

Identification of quantitative trait loci affecting female reproductive traits in a multigeneration Meishan-White composite swine population.

A multigeneration crossbred Meishan-White composite resource population was used to identify quantitative trait loci (QTL) for age at first estrus (AP) and the components of litter size: ovulation rate (OR; number of ova released in an estrous period) and uterine capacity (UC). The population was established by reciprocally mating Meishan (ME) and White composite (WC) pigs. Resultant F1 females were mated to either ME or WC boars to produce backcross progeny (BC) of either 3/4 WC 1/4 ME or 1/4 WC 3/4 ME. To produce the next generation (F3), 3/4 WC 1/4 ME animals were mated to 1/4 WC 3/4 ME animals yielding half-blood (1/2 WC 1/2 ME) progeny. A final generation (F4) was produced by inter se mating F3 animals. Measurements for AP and OR were recorded on 101 BC, 389 F3, and 110 F4 gilts, and UC data were from 101 BC and 110 F4 first parity litters. A genomic scan was conducted with markers (n = 157) spaced approximately 20 cM apart. All parental, F1, BC, and F4 animals but only 84 F3 animals were genotyped and included in this study. The QTL analysis fitted a QTL at 1-cM intervals throughout the genome, and QTL effects were tested using approximate genome-wide significance levels. For OR, a significant (E[false positive] < .05) QTL was detected on chromosome 8, suggestive (E[false positive] < 1.0) QTL were detected on chromosomes 3 and 10, and two additional regions were detected that may possess a QTL (E[false positive] < 2.0) on chromosomes 9 and 15. Two regions possessed suggestive evidence for QTL affecting AP on chromosomes 1 and 10, and one suggestive region on chromosome 8 was identified for UC. Further analyses of other populations of swine are necessary to determine the extent of allelic variation at the identified QTL.

Ovarian function during the estrous cycle of the cow: ovarian blood flow and progesterone release rate.

To study the function of the corpus luteum (CL) through its major secretory product, progesterone (P4), catheters were inserted into the carotid artery (via the facial artery) and the ovarian vein (n = 12), and electromagnetic flow transducers were placed around the ovarian artery in cycling Angus and Hereford cows (n = 6). Blood samples were taken four times daily (at 0600, 1200, 1800 and 2400 h) and ovarian blood flow (OBF) was monitored for 60 min immediately after each blood sampling. After chromatography, P4 was measured by radioimmunoassay. The P4 concentrations in the ovarian vein (OP4) were correlated with day of the estrous cycle (r = .25; P less than .05) and were higher during the morning hours (P less than .05). Arterial progesterone (SP4) was correlated to OP4 (r = .24; P less than .05) and day of the cycle (r = .35; P less than .05). The OBF changed among days (P less than .05). The highest rates were noted during luteal maturation (23 ml/min; SE = .09) and the lowest were noted with the demise of the CL (SP4 less than 1 ng/ml) and approach of estrus (8 ml/min; SE = .07). The OBF was correlated with SP4 (r = .24; P less than .05), although no within-day trends were noted. Exogenous estrone (6 mg) administered via jugular vein decreased OBF within 30 to 45 min, but similar injections of P4 (up to 100 mg) had no effect. Progesterone release (P4R) from the ovary [(OP4 - SP4) x OBF] was higher in the morning hours (P less than .05). The P4 concentration (OP4, SP4) and release (P4R) exhibited wide variations among and within days. The changes in OP4 and P4R were both good indicators of CL development, maturation and regression, as associated with SP4 changes. Oxygen (O2) and carbon dioxide (CO2) concentrations monitored in the carotid artery and ovarian vein indicated that the ovary with the CL was not limited in O2 availability or CO2 removal during periods of low blood flow or high secretion of P4.

GnRH antagonist inhibition of gonadotropin and steroid secretion in boars in vivo and steroid production in vitro.

The hormone GnRH has a stimulatory effect on gonadotropin synthesis and secretion. The objective of the first study was to evaluate concentrations of FSH and LH in plasma of boars after successive treatment with SB75, a GnRH antagonist. Thirteen boars greater than 1 yr of age (eight White Composite [WC] and five Meishan [MS]) were injected once daily with SB75 (10 microg/kg of body weight) for 4 d. Plasma concentrations of LH and testosterone (T) decreased after 1 h from the first dose of SB75. After 12 h of treatment, LH gradually returned to pretreatment concentrations, but T remained suppressed (< 2 ng/mL) until after the last injection of SB75. There was a modest, but significant, reduction in FSH during treatment with SB75. The prolonged inhibitory effect of SB75 on suppression of plasma T concentrations, in the presence of pretreatment concentrations of LH, implied direct effects of SB75 at the testis. In the second experiment, testicular tissue from adult boars was incubated in the presence of three doses of human chorionic gonadotropin (hCG; 0, .5, and 5 IU) with SB75 (250 ng/mL) or with Deslorelin, a GnRH agonist (500 ng/mL). Samples of media were collected every hour for 3 h, and concentrations of T and estrone (E1) were determined by RIA. Concentrations of T and E1 increased with time in response to treatment with hCG. Co-treatment with SB75 decreased media concentrations of T (P < .01) and E1 (P < .03) compared to controls (77.9 vs 85.7 +/- 2.0 and 4.7 vs 5.3 +/- .2 ng/g). In contrast, treatment with Deslorelin had no effect on the amount of T (P > .50) or E1 (P > .26) released with all dosages of hCG. These results indicate that a GnRH antagonist has a direct effect on the testis, decreasing amounts of T and E1 released from the Leydig cells; however, treatment with a GnRH agonist had no direct effect on release of these gonadal steroids. Thus, it remains unresolved whether the site of action of GnRH antagonist on testicular steroidogenesis is through a testicular GnRH receptor or through some other mechanism.

Assessment of pubertal development of boars derived from ultrasonographic determination of testicular diameter.

At the onset of puberty, seminiferous tubules rapidly increase in diameter, thereby occupying a greater proportion of the testis, resulting in a rapid increase in testicular size. The objective of the current studies was to evaluate ultrasonography for assessing testicular diameter, as a basis for ranking boars relative to their extent of pubertal development. In the initial study, prior to castration at 4, 5, 6, or 7 mo of age, testicular length and diameter were assessed by ultrasonography in 160 anesthetized boars. After castration, testes were weighed. Mean diameter of seminiferous tubules and percentage of the testis occupied by tubules were determined by histological evaluations of all testes. Testicular volume was calculated from length and diameter and was correlated with testicular weight (P < 0.001; r ≧ 0.78) within each of the four age groups. At 4 and 5 mo of age, testicular diameter correlated positively (P < 0.001) with diameter of seminiferous tubules; this relationship was not significant at older ages. In two subsequent studies, testicular diameter determined ultrasonographically in conscious boars was highly correlated (r > 0.8) when assessed twice on the same day, or when diameter of the right was compared with diameter of the left testis. Similarly, testicular diameter obtained initially at 92 d of age correlated positively (P < 0.001) with the diameter observed at older ages, but the magnitude of the relationship decreased as time between evaluations increased. These findings supported ultrasonographic determination of testicular diameter during early pubertal development, as a means to rank boars of similar chronological age for extent of pubertal development.