Contributions of the maternal uterine environment and piglet genotype on weaning survivability potential: II. Piglet growth, lactation performance, milk composition, and piglet blood profiles during lactation following reciprocal embryo transfers between Meishan and White crossbred gilts.

Crossbreeding studies between Meishan (MS) and Large White (LW) pigs have illustrated that increased piglet growth before weaning is attributed to the maternal genotype of LW dams. The objective of this study was to determine the contributions of the maternal uterine environment (MUE), piglet genotype (PigG), piglet age (PA), and their interactions on piglet growth, lactation performance, milk composition, and piglet blood profiles during lactation following reciprocal embryo transfers between MS and White crossbred (WC) gilts. Twenty-five successful pregnancies were generated by embryo transfer in 2 farrowing years representing all MUE × PigG combinations: MS × MS (n = 4 litters), MS × WC (n = 7 litters), WC × MS (n = 7 litters), and WC × WC (n = 7 litters). At d 1 and 10 and at weaning, piglets (n = 147, n = 96, and n = 94, respectively) were weighed and blood samples were collected and measured for hematocrit, hemoglobin, glucose, nitrogen, NEFA, albumin, lactate, and cortisol. In addition, sows were manually milked from a medial mammary gland to determine milk composition. All data were analyzed by ANOVA using MIXED model procedures with the fixed effects of MUE, PigG, PA, and their interactions. Piglet weight was greater (P < 0.001) in piglets from WC dams compared to MS dams at d 10 and weaning but not at d 1. In addition, ADG were greater (P < 0.05) from piglets from WC dams compared to MS dams throughout lactation. However, milk composition was greater (P < 0.05) for GE and fat content from MS dams compared to WC dams, illustrating differences in milk quality between the breeds. There were significant MUE × PigG × PA interactions for hematocrit and hemoglobin levels in which greater (P < 0.001) levels were observed in MS piglets, irrespective of MUE, at d 1 of lactation and in MS piglets from MS dams at d 10 of lactation. Blood glucose was greater (P = 0.01) at d 1 in piglets from WC dams regardless of PigG but, at weaning, glucose was greater (P = 0.01) in WC piglets regardless of MUE. Serum NEFA levels were greater (P = 0.02) in piglets from MS dams throughout the lactation period. This study demonstrated that WC dams were superior to MS dams for piglet growth during lactation, in agreement with previous crossbreeding studies. However, blood components measured displayed complex interactions between the piglet and maternal breed, which signify possible mechanisms for improved preweaning survivability but slower lactational growth of MS piglets.

Preliminary evidence for the features of non-reducible discogenic low back pain: survey of an international physiotherapy expert panel with the Delphi technique.

OBJECTIVES: The lumbar intervertebral disc is a known source of low back pain (LBP). Various clinical features of discogenic pain have been proposed, but none have been validated. Several subgroups of discogenic pain have been hypothesised, with non-reducible discogenic pain (NRDP) proposed as a relevant clinical subgroup. The objectives of this study were to obtain consensus from an expert panel on the features of discogenic low back pain, the existence of subgroups of discogenic LBP, particularly NRDP, and the associated features of NRDP. DESIGN: Three-round Delphi survey. PARTICIPANTS: Twenty-one international physiotherapists with expertise in LBP. METHODS: Panellists listed and ranked features that they believed to be indicative of discogenic pain and NRDP. On completion of Round 3, features with ≥50% agreement between panellists were deemed to have reached consensus. RESULTS: After three rounds, 10 features of discogenic LBP were identified. Nineteen of the panellists believed that NRDP was a subgroup of discogenic LBP, and nine features of NRDP were identified. CONCLUSION: This study provides preliminary validation for the features associated with discogenic LBP. It also provides evidence supporting the existence and features of NRDP as a separate clinical subgroup of discogenic LBP.

Contributions of the maternal uterine environment and piglet genotype on weaning survivability potential: I. Development of neonatal piglets after reciprocal embryo transfers between Meishan and White crossbred gilts.

In commercial pigs, the greatest susceptibility for pre-weaning mortality occurs in low birth-weight piglets. Despite their overall decreased birth weight, Meishan (MS) piglets have decreased pre-weaning mortality rates compared with contemporary Western breeds. The objective of the current study was to determine the contributions of the maternal uterine environment, piglet genotype, and their interaction on the development of neonatal piglets pertaining to pre-weaning survivability using reciprocal embryo transfer between MS and White crossbred (WC) pigs. Twenty-five successful pregnancies were produced from 2 farrowing seasons, generating litters of maternal uterine environment (MUE) by piglet genotype (PigG) combinations; MS × MS (n = 4 litters), MS × WC (n = 7 litters), WC × MS (n = 7 litters), and WC × WC (n = 7 litters). At approximately 24 h of age (Day 1), piglets (n = 173) were weighed and a blood sample was taken. Hematocrit, hemoglobin, glucose, plasma urea nitrogen, albumin, NEFA, lactate, and cortisol were measured in all blood samples. Representative piglets (n = 46) from each litter were harvested and body measurements (i.e., organ weights, tissue glycogen content, and body composition) were determined. Piglet data were analyzed by ANOVA using MIXED model procedures. Both MUE (P < 0.001) and PigG (P < 0.01) affected piglet BW, illustrating that piglets gestated in WC gilts were heavier than piglets gestated in MS gilts, and WC piglets were heavier than MS piglets. Serum albumin concentrations were increased (P < 0.05) in MS piglets compared with WC piglets, indicating greater liver maturity. Significant MUE × PigG interactions were observed for hematocrit and hemoglobin, in which the greatest concentrations were observed in MS piglets gestated in MS and WC gilts, and the lowest concentrations were observed in WC piglets gestated in WC gilts, demonstrating increased oxygen-carrying capability. The percentage of fat and nitrogen, as well as the GE of the body, were greater (P < 0.05) in MS piglets, indicating greater energy stores. Liver, bicep femoris, and LM glycogen concentrations were greater (P < 0.01) in WC piglets compared with MS piglets, demonstrating increased glycogen catabolism in MS piglets. This study demonstrated limited interactions between the maternal uterine environment and piglet genotype on weaning survivability potential, suggesting that the MS piglet is a viable model for pre-weaning survivability.

Plenary contribution to International Conference on Boar Semen Preservation 2011. Genetic selection for freezability and its controversy with selection for performance.

Little data are available in the literature regarding freezability of boar sperm or its relationship with other traits. Existing data suggest the trait would respond favourably to selection, and information is available from other species suggesting components that might have changed. Genetic parameters are estimated for boar sperm freezability including heritability and correlations with other production traits. Sperm freezability is an ideal candidate for marker assisted-selection or selection for favourable alleles.

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.

Association of allelic variants of thyroid-binding globulin with puberty in boars and responses to hemicastration.

Hemicastration of males increases weight of remaining testis when conducted before Sertoli cells cease to proliferate. The current studies re-examined responses to hemicastration in one-quarter Meishan crossbred boars that differed for two alleles of thyroid-binding globulin (TBG). In the first experiment, boars at 25 days of age with either allele did not differ in degree of testicular development; however, at 56 days, boars with the C allele had more advanced testicular development than littermates with the A allele as evidenced by testes with seminiferous tubules of larger diameter (P<0.008) and greater weight (P<0.05). At 10 months of age, boars hemicastrated at 25 days had a similar number of Sertoli cells in their single testis compared with both testes of control boars. However, in boars hemicastrated at 56 days number of Sertoli cells was less than the total number of Sertoli cells in the bilaterally intact controls; this reduction was greater (P<0.05) in boars with the C allele than in those with the A allele. The second experiment confirmed earlier (P<0.05) pubertal development in boars with the C allele relative to littermates with the A allele based on larger tubular diameter and the greater proportion of tubules with a distinct lumen at 60 and 80 days of age. These studies establish that boars with the C allele for TBG attain puberty at a younger age than those with the A allele thereby linking rate of pubertal development of boars with TBG or with gene(s) on the X chromosome in close proximity of TBG.

Sertoli cell differentiation in pubertal boars.

Meishan boars experience puberty at a younger age than crossbred boars in association with earlier expansion of seminiferous tubules and smaller postpubertal testicular size. The current study defined changes in expression, assessed by immunohistochemistry, of anti-Mullerian hormone (AMH) and CDKN1B, markers of Sertoli cell differentiation, in prepubertal Meishan and crossbred (BX) boars and related these changes with the pubertal expansion of seminiferous tubules. Expression of AMH in tubules of Meishan and BX boars increased (P < 0.002) from 7 to 28 d of age. Pubertal development was characterized by declining AMH expression (P < 0.001), followed by increasing (P < 0.001) expression of CDKN1B in Sertoli cell nuclei and subsequent expansion of tubules. These pubertal changes occurred at younger (P < 0.001) ages in Meishan than in BX boars. In testes of 90-d-old BX boars, expression of CDKN1B in Sertoli cell nuclei and tubular diameter increased (P < 0.001) from the mediastinum outwardly toward the tunica. Evaluation of the same tubules in adjacent sections established that expression of AMH decreased followed by expression of CDKN1B in Sertoli cell nuclei; both changes occurred before tubular diameter achieved 90 microm. In BX boars unilaterally castrated at 90 d of age, tubular diameter was inversely related to weight of the remaining testis at 10 mo (P < 0.05), supporting terminal differentiation of Sertoli cells in a subpopulation of these boars. These studies established temporal relationships of AMH, CDKN1B, and seminiferous tubule diameter in pubertal boars of 2 genetically diverse lines and determined that differentiation of Sertoli cells during pubertal development progresses as a gradient from the mediastinum outwardly toward the tunica.

Porcine hypothalamic aromatase cytochrome P450: isoform characterization, sex-dependent activity, regional expression, and regulation by enzyme inhibition in neonatal boars.

Domestic pigs have three CYP19 genes encoding functional paralogues of the enzyme aromatase cytochrome P450 (P450arom) that are expressed in the gonads, placenta, and preimplantation blastocyst. All catalyze estrogen synthesis, but the gonadal-type enzyme is unique in also synthesizing a nonaromatizable biopotent testosterone metabolite, 1OH-testosterone (1OH-T). P450arom is expressed in the vertebrate brain, is higher in males than females, but has not been investigated in pigs, to our knowledge. Therefore, these studies defined which of the porcine CYP19 genes was expressed, and at what level, in adult male and female hypothalamus. Regional expression was examined in mature boars, and regulation of P450arom expression in neonatal boars was investigated by inhibition of P450arom with letrozole, which is known to reprogram testicular expression. Pig hypothalami expressed the gonadal form of P450arom (redesignated the "gonadal/hypothalamic" porcine CYP19 gene and paralogue) based on functional analysis confirmed by cloning and sequencing transcripts. Hypothalamic tissue synthesized 1OH-T and was sensitive to the selective P450arom inhibitor etomidate. Levels were 4-fold higher in male than female hypothalami, with expression in the medial preoptic area and lateral borders of the ventromedial hypothalamus of boars. In vivo, letrozole-treated neonates had increased aromatase activity in hypothalami but decreased activity in testes. Therefore, although the same CYP19 gene is expressed in both tissues, expression is regulated differently in the hypothalamus than testis. These investigations, the first such studies in pig brain to our knowledge, demonstrate unusual aspects of P450arom expression and regulation in the hypothalamus, offering promise of gaining better insight into roles of P450arom in reproductive function.

Growth and pubertal development of F1 bulls from Hereford, Angus, Norwegian Red, Swedish Red and White, Friesian, and Wagyu sires.

The objective of the study was to characterize body growth, testicular development, and puberty from 8 to 14 mo of age in bulls (n = 120) produced by mating sires from Hereford, Angus, Norwegian Red, Swedish Red and White, Friesian, and Wagyu breeds to MARC III ((1/4) Hereford, (1/4) Angus, (1/4) Red Poll, and (1/4) Pinzgauer) cows. Traits evaluated were birth weight, weaning weight (at 215 d), yearling weight, ADG from 8 to 14 mo of age, paired testicular volume growth from 8 to 14 mo of age, age at puberty (determined by production of 50 x 10(6) sperm with 10% motility), age at freezable semen (determined by production of 500 x 10(6) sperm with 50% motility), and, at 15 mo of age, paired testicular weight and daily sperm production per testis pair. There was an effect of sire breed (P = 0.03) for age at puberty; animals with Wagyu and Swedish Red and White inheritance reached puberty at a later date (302 and 302 d of age, respectively) compared with Angus-sired bulls (268 d). Age at puberty for Hereford-, Norwegian Red-, and Friesian-sired bulls was 270, 271, and 278 d, respectively. Differences in BW were observed (P = 0.03) at birth; bulls with Hereford and Friesian were heavier at birth (43 and 41 kg, respectively) compared with those with Norwegian Red, Swedish Red and White, and Wagyu inheritance (39, 38, and 38 kg, respectively). Differences in BW were also observed at 1 yr of age (P = 0.001), where the heaviest animals were those sired by Angus (450 kg), whereas the lightest animals were those sired by Wagyu (403 kg). Bulls with Wagyu inheritance had the lowest (P = 0.04) ADG (1.12 kg/d) compared with bulls with inheritance from Hereford (1.22 kg/d), Angus (1.28 kg/d), Norwegian Red (1.24 kg/d), Swedish Red and White (1.25 kg/d), and Friesian (1.27 kg/d). Differences in scrotal growth rate were not significant (P = 0.99). They ranged from 1.95 in Angus-sired to 1.66 cm3/d in Wagyu-sired bulls. There were no differences (P = 0.80) for age at freezable semen (335 +/- 10 d). At slaughter (15 mo of age), there were no differences (P = 0.62) for paired testicular weight (603 +/- 28 g) and daily sperm production (10.6 x 10(9) +/- 0.9 x 10(9) per testis pair). Growth of bulls with Wagyu inheritance was slower, and bulls with Wagyu or Scandinavian inheritance reach puberty at an older age than bulls with Angus inheritance.

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.

Genetic variation in sperm production.

In boars, the primary determinant of daily sperm production is the number of Sertoli cells, which establishes testicular weight. The only breed comparison of foetal testicular development in boars contrasted two diverse breeds, White composite (WC, Landrace-Yorkshire) with Meishan, a Chinese breed that undergoes pubertal development at a young age and has small testicular size. During the prenatal period, the pattern of change in testicular development is similar in these two breeds with both having their greatest proportion of proliferating Sertoli cells at 90 days of gestation, and with WC boars possessing more Sertoli cells and greater mass of seminiferous tubules during the latter half of gestation. During the first month of life, Meishan boars accumulate Sertoli cells and mass of seminiferous tubules at a greater rate than WC boars, and Meishan boars undergo terminal differentiation of Sertoli cells at a younger age. Postpubertal boars, within each breed and crossbreds of the two breeds, with small testicular size have increased circulating concentrations of follicle-stimulating hormone. No direct breed comparisons of testicular development are apparent for postpubertal boars of other breeds. Accepting the limitations of data reported from different laboratories, Piau boars reach puberty at an older age and have a greater proportion of their testes occupied with seminiferous tubules than Meishan boars; both breeds have small testes. A gene or genes on the X chromosome code for small testicular size in Meishan crossbred boars; genetic determinants of testicular size and sperm production in other breeds remain to be identified.

Deciphering the pig genome to understand gamete production.

The field of livestock genomics has made considerable advances in the past decade. In the area of pig reproduction, a number of genome scans have identified several genomic regions associated with variation in reproductive measures ranging from ovulation rate, litter size and testis size. Additionally, several candidate genes have been associated with variation in litter size. These studies primarily focused on developing genetic markers to facilitate selection decisions. To date, their results have made minor contributions to commercial pig performance and our knowledge on the inheritance of complex phenotypes. With the availability of additional resources for pig, as well as from human and mouse studies, future studies should be directed to identifying genetic variation that affects biological processes. To reach this goal, teams of diversely trained scientists need to be formed that include geneticists, physiologists, molecular biologists and bioinformaticists. A diversified team of scientists equipped with all of the available research tools (genomic sequence data, expression arrays, knowledge of gene product functions, etc.) and appropriate swine populations should be able to decode the genome's hidden secrets on how it controls reproductive processes.

Testicular development of Zebu bulls after chronic treatment with a gonadotropin-releasing hormone agonist.

The objective was to compare testis characteristics of Zebu bulls treated with the GnRH agonist, deslorelin, at different times and for different durations during their development. An additional objective was to determine the usefulness of a stain for the transcription factor GATA-binding protein 4 (GATA-4) as a specific marker for Sertoli cell nuclei in cattle. Bulls (54) were allocated to nine groups (n = 6) and received s.c. deslorelin implants as follows: G1 = from birth to 3 mo of age; G2 = from 3 to 6 mo; G3 = from 6 to 9 mo; G4 = from 9 to 12 mo; G5 = from birth to 15 mo; G6 = from 3 to 15 mo; G7 = from 6 to 15 mo; G8 = from 12 to 15 mo; and G9 (control) = no implant. Bulls were castrated at 19 mo of age. Paraffin sections (10 microm) were subjected to quantitative morphometry and GATA-4 immunohistochemistry. At castration, all bulls in the control group (6/6) had attained puberty (scrotal circumference > or = 28 cm), whereas a smaller proportion (P < 0.05) had reached puberty in G2 (2/5) and G6 (1/6). Bulls in G2 and G6 also had a lesser (P < 0.05) testis weight compared with the control group. Total volume of seminiferous epithelium and total daily sperm production in G2 and G6 were only half that observed in the control group. Spermatids were observed in less than 50% of seminiferous tubules in G2, G6, and G7 compared with 82% in the control group (P < 0.05). Staining for GATA-4 was specific for and abundant in the Sertoli cell nucleus in both pre- and postpubertal bulls, and no other cell nucleus inside the seminiferous tubule was positive for GATA-4. Total number of Sertoli cells was not affected by treatment (P = 0.45), but nuclear volume was smaller in G2 and G6 (P < 0.05) compared with the control group. In conclusion, treatment of Zebu bulls with deslorelin had no apparent beneficial effect on testis development and delayed puberty when treatment was initiated at 3 mo of age. Staining for GATA-4 was a useful method for identifying and quantifying Sertoli cell nuclei in both pre- and postpubertal bulls.

Follicular development and maturation in gilts selected for an index of high ovulation rate and high prenatal survival.

Seventy-one 10th-generation gilts from White Line-1 (WL-1 = randomly selected control line) and White Line-2 (WL-2 = selected for an index of ovulation rate and prenatal survival rate) were used to compare the pattern of follicular development and atresia during the follicular phase of the estrous cycle. Gilts were treated with PGF(2alpha)on d 13 of the estrous cycle (d 0 of induced follicular development) to induce luteolysis and assigned randomly within line and sire for ovary recovery on d 0, 2, 3, 4, 5, and the day after estrus. Ovaries were evaluated for numbers of corpora albicantia and small (2 to 2.9 mm), medium (M1 = 3 to 4.9 mm; M2 = 5 to 6.9 mm), and large (>or=7 mm) follicles. The concentration of estradiol-17beta in follicular fluid was used to classify individual M2 and large follicles as estrogen-active (>or=100 ng of estradiol-17beta/mL) or inactive (<100 ng of estradiol-17beta/mL). The WL-2 gilts had a greater ovulation rate than WL-1 gilts at their pre-treatment estrus (20.4 vs. 13.8 corpora albicantia; P < 0.001). The small and M1 follicle populations decreased rapidly in both lines over time (P < 0.001). The M2 follicle population increased in both lines between d 0 to 4 and then decreased. Mean estradiol concentration of M2 follicles increased in both genetic lines over time (P < 0.02). All large follicles were estrogen-active in both lines; the number of large follicles increased with day (P < 0.001) and was similar in both lines. The number of estrogen-active M2 follicles was similar in both lines, increasing to d 3 and 4 and then decreasing (P < 0.01) thereafter. However, the total number of estrogen-active follicles (sum of estrogen-active M2 and large follicles) was greater in WL-2 than in WL-1 gilts (P < 0.04), increasing to the ovulatory potential by d 3 in WL-1 gilts, but continuing to increase through d 4 in WL-2 gilts. Selection of an additional six ovulatory follicles from the estrogen-active M2 follicle pool after d 5 was required in both lines to achieve the projected ovulation rate, and after estrus, the number of large follicles remained insufficient to attain the ovulatory potential of each line.

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.

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.

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.

Biochemical assessment of limits to estrogen synthesis in porcine follicles.

Limits to estrogen production by early and late preovulatory porcine follicles were assessed by comparing enzymatic capacities for androgen (17,20-lyase) and estrogen (aromatase) synthesis in theca interna and granulosa, support of enzyme activities by the redox partner proteins NADPH-cytochrome P450 oxidoreductase (reductase) and cytochrome b5, and tissue-specific expression and regulation of these proteins. Parameters included follicular fluid (FF) estradiol and progesterone levels, theca and granulosa aromatase and reductase activities, and theca 17,20-lyase activity. Expression of proteins responsible for these activities, aromatase (P450arom) and 17 alpha-hydroxylase/17,20-lyase (P450c17) cytochromes P450, reductase, and for the first time in ovarian tissues cytochrome b5, were examined by Western immunoblot and immunocytochemistry. Theca and granulosa aromatase activities were as much as 100-fold lower than theca 17,20-lyase activity, but aromatase was correlated with only the log of FF estradiol. Granulosa reductase activity was twice that of the theca, and cytochrome b5 expression was clearly identified in both the theca and granulosa layers, as was P450arom, but was not highly correlated with either 17,20-lyase or aromatase activities. Reductase expression did not change with stage of follicular development, but cytochrome b5, P450c17, and P450arom were markedly lower in post-LH tissues. These data indicate that aromatase and not 17,20-lyase must limit porcine follicular estradiol synthesis, but this limitation is not reflected acutely in FF steroid concentrations. Neither reductase nor cytochrome b5 appear to regulate P450 activities, but the expression of cytochrome b5 in granulosa and theca suggests possible alternative roles for this protein in follicular development or function.

Relationships of testicular iron and ferritin concentrations with testicular weight and sperm production in boars.

The inverse relationship of testicular size and circulating follicle-stimulating hormone (FSH) concentrations has been documented, and accompanying this relationship is the change in color of the parenchymal tissue of the testes. Large testes (300 to 400 g) are pink to light red and small testes (100 g) are dark maroon with color gradations for weights in between. It was hypothesized that this color most likely represented an iron protein. Chromatographic analysis of testicular tissue indicated that the Fe was associated primarily with ferritin, and immunohistochemistry showed that Leydig cells were the primary location of ferritin storage within the testes. Concentrations of Fe and ferritin were higher in small testes and decreased as testes weight increased (P < 0.05). As testicular Fe concentrations increased, daily sperm production (DSP) and total DSP declined (P < 0.05). Genotyping six generations of Meishan x White composite boars (n = 288) for a quantitative trait locus that is indicative of elevated FSH and small testes in boars indicated that the Meishan genotype had elevated testicular iron concentrations and darker color in conjunction with reduced total DSP (P < 0.01). It is not thought the elevated iron concentrations affect testicular weights but are probably a result of elevated FSH and FSH inducement of Fe transport. The storage of Fe in Leydig cells may provide a reservoir of Fe for easy access by Sertoli and germ cells, but still provide a degree of protection to germ cells from ionic iron.

Sertoli cells in the boar testis: changes during development and compensatory hypertrophy after hemicastration at different ages.

Changes in Sertoli cell numbers and testicular structure during normal development and compensatory hypertrophy were assessed in crossbred Meishan x White Composite males. Boars were assigned at birth to unilateral castration at 1, 10, 56, or 112 days or to remain as intact controls through 220 days. The first testes removed were compared to assess testicular development. At 220 days, testicular structure was evaluated in boars representing the 25% with the largest (Lg) testis and the 25% with the smallest (Sm) testis in each treatment group. The number of Sertoli cells per testis reached a maximum by Day 56 in Sm testis but not until Day 112 in Lg testis boars, indicating a longer duration of Sertoli cell proliferation in Lg testis boars. Unilateral castration of Lg testis boars on Days 1, 10, 56, and 112 caused the weight of the remaining testis to hypertrophy by 149%, 135%, 119%, and 120%, respectively, and total sperm production to increase to 127%, 128%, 97%, and 106%, respectively. However, Sertoli cell numbers changed little in hemicastrate boars. In Lg testis boars, compensatory hypertrophy primarily involved proliferation of Leydig cells and expansion of existing Sertoli cells with little increase in Sertoli cell numbers, but in Sm testis boars, it involved expansion of existing Leydig and Sertoli cells without increase in cell numbers. These results indicate that Lg and Sm testis boars display intriguing differences during both development and compensatory hypertrophy, and they identify a unique animal model for further studies of factors that program and control Sertoli cell proliferation.