No abstract

The positive relationship between Sertoli cell number and testicular size emphasizes the importance of determining factors involved in the regulation of the Sertoli cell population. Based on data from other species and indirect evidence in the boar, it is generally accepted that porcine Sertoli cells proliferate rapidly throughout the early postnatal period. However, direct evaluation of Sertoli cell number and the proliferative activity of Sertoli cells during the early postnatal period in boars have not been reported. Stereological enumeration of Sertoli cells is a labor-intensive process and would be greatly facilitated by a marker for these cells especially in the sexually mature male. Thus, the first objective of this study was to determine if expression of the transcription factor GATA-4 is an effective marker for fetal, postnatal, and adult Sertoli cells to facilitate enumeration procedures. The second objective was to evaluate the proliferative activity and growth of the Sertoli cell population in neonatal White Composite and Meishan boars, known to differ in mature testis size and Sertoli cell number, to determine the importance of this developmental period for the adult Sertoli cell population. GATA-4 was abundantly expressed by Sertoli cells throughout fetal and prepubertal stages of development and specifically stained both type A and B Sertoli cell nuclei in the sexually mature boar. Immunoreactivity was never observed in the germ cells regardless of their stage of development, illustrating that GATA-4 is a useful marker for both developing and adult Sertoli cells in the boar. Testicular size did not differ between breeds on Day 1 postpartum, but by 14 days postpartum White Composite boars had significantly larger testes compared to Meishan boars (P: < 0.001). Similarly, Sertoli cell number did not differ between breeds at 1 day postpartum; however, at 14 days postpartum White Composite boars had a significantly larger Sertoli cell population compared to Meishan boars (P: < 0.05). Surprisingly, despite having more Sertoli cells than Meishan boars at 14 days postpartum, the proportion of actively proliferating Sertoli cells in the White Composite boars was almost 50% less than the Meishan boars. This result illustrates that rapid rates of Sertoli cell proliferation probably occurred prior to 14 days postpartum in the White Composite boars. Collectively, these results illustrate that the relationship between testicular size and Sertoli cell number is manifested very early in the postnatal period for these two breeds. The substantial difference in the size of the Sertoli cell population and their proliferative activity between Meishan and White Composite boars during the early postnatal period emphasizes the importance of this early period for the establishment of the Sertoli cell population and subsequent adult testicular size.

Chinese breeds of swine are known for their reproductive prolificacy and are noted for large litter size. The current investigation evaluated reproductive components of three breeds of Chinese boars in comparison to a contemporary site breed common in the U.S. Semen from postpubertal Duroc, Meishan, Fengjing, and Minzhu boars was collected during four seasons of the year. After each semen collection and evaluation period, boars were weighted and placed in a restraining chute for testicular measurements and blood sampling for measurement of FSH, testosterone, and inhibin. Although Duroc boars were 2 mo younger than Chinese boars, initial and final body weight and paired testis volume in Durocs were greater (p < 0.05) than in Chinese boars. Total spermatozoa per ejaculate was similar for Duroc and Minzhu boars, but was lower (p < 0.05) in Fengjing and Meishan boars. Progressive motility and sperm morphological characteristics were not affected by breed of boar. Serum FSH concentrations were markedly higher (p < 0.01) in Meishan and Fengjing boars than in other breeds, and concentrations were nearly 8-fold higher in Meishan than in Duroc boars. Breed differences in serum inhibin were essentially the inverse of those observed for FSH, with Durocs exhibiting the highest inhibin concentrations and Meishans exhibiting the lowest. Testosterone values were not different between breeds. However, testosterone concentrations fluctuated with season, and serum testosterone was highest during the fall of the year in all breeds. These results indicated that some reproductive characteristics differ dramatically between Duroc and Chinese breeds of boars. Breed differences existed in body size, testis size, sperm per ejaculate, ejaculate volume, and serum FSH and inhibin concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparisons of numbers of antral ovarian follicles and corpora lutea (CL), of blood hormone concentrations, and of follicular fluid steroid concentrations and IGFBP activity were conducted between cows selected (twinner) and unselected (control) for twin births to elucidate genetic differences in the regulation of ovarian follicular development. Ovarian follicular development was synchronized among cows by a single i.m. injection of PGF2alpha on d 18 of the estrous cycle; six cows per population were slaughtered at 0, 24, 48, and 72 h after PGF2alpha. Jugular vein blood was collected from each animal at PGF2alpha injection and at 24-h intervals until slaughter. Ovaries of twinner cows contained more small (< or = 5 mm in diameter, P < 0.05), medium (5.1 to 9.9 mm, P < 0.05), and large (> or = 10.0 mm, P < 0.01) follicles and more (P < 0.01) CL than ovaries of controls. Follicular fluid concentrations of estradiol, androstenedione, testosterone, and progesterone reflected the stage of follicular development and were similar for twinner and control follicles at the same stage. Earlier initiation of follicular development and/or selection of twin-dominant follicles in some twinner cows resulted in greater concentrations of estradiol in plasma at 0, 24, and 48 h and of estradiol, androstenedione, and testosterone in follicular fluid of large follicles at 0 h after PGF2alpha for twinner vs. control cows (follicular status x time x population, P < 0.01). Binding activities of IGFBP-5 and -4 were absent or reduced (P < 0.01) in follicular fluid of developing medium and large estro-gen-active (estradiol:progesterone ratio > 1) follicles but increased with atresia. Only preovulatory Graafian follicles lacked IGFBP-2 binding, suggesting a possible role for IGFBP-2 in selection of the dominant follicle. Concentrations of IGF-I were twofold greater (P < 0.01), but GH (P = 0.10) and cholesterol (P < 0.05) were less in blood of twinners. Three generations of selection of cattle for twin ovulations and births enhanced ovarian follicular development as manifested by increased numbers of follicles within a follicular wave and subsequent selection of twin dominant follicles. Because gonadotropin secretion and ovarian steroidogenesis were similar for control and twinner cattle, enhanced follicular development in twinners may result from decreased inhibition by the dominant follicle(s), increased ovarian sensitivity to gonadotropins, and/or increased intragonadal stimulation, possibly by increased IGF-I.

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.