Rats were considered to be pubertal at 50 days of age when spermatozoa were first found in the tail of the epididymis. Sperm production/g testis increased up to 75 days of age and testicular weight increased until 100 days of age. Sperm reserves in the tail of the epididymis were not maximal until 100 days of age. Therefore, Wistar rats are not sexually mature until 100 days. Sexually mature rats had testes weighing 3.7 g, produced 86 x 10(6) spermatozoa or 24 x 10(6) spermatozoa/g testicular parenchyma daily, and their paired epididymides contained 295 x 10(6) spermatozoa in the head + body and 440 x 10(6) spermatozoa in the tail.

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Daily sperm production and epididymal sperm reserves of pubertal and adult rats.

A repeatable procedure for fertilization of bovine ova in vitro is described. Oocytes were recovered from ovarian follicles or from oviducts near the time of ovulation following treatment of donors with pregnant mare's serum gonadotropin (PMSG) and prostaglandin F2 alpha (PGF2 alpha). For in vitro capacitation semen was incubated, then high ionic strength treated and subsequently incubated in defined medium prior to insemination of oocytes. In one experiment frozen bull semen was successfully used. In experiments with 4 bulls (B, C, D, F), 34 (43.6%) of 78 ova and 13 (19.7%) of 66 follicular oocytes were fertilized in vitro. In the last series (spermatozoa from Bull F) the fertilization of 22 (62.9%) of 35 tubal ova was achieved. In vitro development proceeded to the 8-cell stage. No fertilization in vitro followed use of one male (Bull E), even though his spermatozoa could penetrate zona-free hamster ova in vitro, and higher than usual bacterial contamination of his semen was implicated as the probable cause. Findings suggested vigorous progressive sperm motility and acrosome integrity to be important features of good sperm samples. In one experiment a 4-cell stage embryo was transferred with the result that the recipient gave birth to a normal bull calf on June 9, 1981. The first calf resulting from in vitro fertilization has been found to be completely normal.

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Normal development following in vitro fertilization in the cow.

This review addresses current understanding of the germline stem cell niche unit in mammalian testes. Spermatogenesis is a classic model of tissue-specific stem cell function relying on self-renewal and differentiation of spermatogonial stem cells (SSCs). These fate decisions are influenced by a niche microenvironment composed of a growth factor milieu that is provided by several testis somatic support cell populations. Investigations over the last two decades have identified key determinants of the SSC niche including cytokines that regulate SSC functions and support cells providing these factors, adhesion molecules that influence SSC homing, and developmental heterogeneity of the niche during postnatal aging. Emerging evidence suggests that Sertoli cells are a key support cell population influencing the formation and function of niches by secreting soluble factors and possibly orchestrating contributions of other support cells. Investigations with mice have shown that niche influence on SSC proliferation differs during early postnatal development and adulthood. Moreover, there is mounting evidence of an age-related decline in niche function, which is likely influenced by systemic factors. Defining the attributes of stem cell niches is key to developing methods to utilize these cells for regenerative medicine. The SSC population and associated niche comprise a valuable model system for study that provides fundamental knowledge about the biology of tissue-specific stem cells and their capacity to sustain homeostasis of regenerating tissue lineages. While the stem cell is essential for maintenance of all self-renewing tissues and has received considerable attention, the role of niche cells is at least as important and may prove to be more receptive to modification in regenerative medicine.

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The Germline Stem Cell Niche Unit in Mammalian Testes

Methods for assessing sperm motility, morphology, and counts in the rat, rabbit, and dog: a consensus report. ILSI Risk Science Institute Expert Working Group on Sperm Evaluation.

This paper highlights the most critical aspects of the problem of predicting fertility. To determine if a laboratory test(s) is highly correlated with fertility it is essential to have: a) specific, precise and accurate laboratory tests, and b) precise and accurate fertility data. Acquisition of precise and accurate data for laboratory tests and fertility of spermatozoa in the same sample is not easy. Data derived from in vitro fertilization are not tests of fertility, because only a subset of the attributes important for fertilization in vivo are tested. Because of deficiencies in fertility data, there probably is no valid report for human spermatozoa correlating results of laboratory tests and fertility, and very few valid studies for laboratory or domesticated animals. There is little doubt that objective measures of sperm motion, acrosomal status, or other characteristics are significantly correlated with fertility. However, establishment of the correlations between a group of attributes and fertility is not the question of interest. The goal is prediction of fertility. There has been no recent effort to develop a prediction of fertility or fecundity based on sperm characteristics, and achievement of this goal may be elusive.

Can the fertility potential of a seminal sample be predicted accurately

Fifty-two Holstein bulls were castrated at 12, 16, 20, 24, 28 or 32 weeks to (1) determine whether testicular development is influenced by season of birth (April or October) and (2) examine quantitatively the establishment of spermatogenesis Season of birth (spring or fall) did not influence (P less than 05) either testis weight at castration or the establishment of spermatogenesis With age held constant, scrotal circumference and testis weight were correlated (79; p less than 05) Testis weight increased from 9 +/- 1 g at 12 weeks to 117 +/- 10 g at 32 weeks of age Seminiferous tubules occupied 44% of the testicular parenchyma at 12 weeks and 81% at 32 weeks Differentiation of basal indifferent supporting cells to Sertoli cells started at 20 weeks, and formation of Sertoli cells was completed near 28 weeks Gonocytes predominated at 12 weeks, but by 20 weeks most had been replaced by prespermatogonia and A-spermatogonia Thus, transformation from a prepubertal testis to a pubertal testis containing Sertoli cells and A-spermatogonia occurred between 16 and 24 weeks (testis weight = 18 to 42 g) Preleptotene to diplotene spermatocytes appeared sequentially between 16 and 28 weeks and their numbers increased through 32 weeks Significant numbers of pachytene spermatocytes and spermatids were not present before 28 and 32 weeks, respectively Establishment of spermatogenesis was completed by 32 weeks (testis weight less than 80 g) Testes weighing less than 80 g were producing few if any sperm Thus, the establishment of spermatogenesis was progressive, associated with more than a fourfold increase in testis weight, and occurred over a period of about 16 weeks

Testicular Development and Establishment of Spermatogenesis in Holstein Bulls

The Male Rabbit. III. Determination of Daily Sperm Production by Means of Testicular Homogenates

The temporal pattern of the endocrine changes associated with puberty were studied using 52 bulls born in October or April. Blood samples were taken weekly and at 30-min intervals for 5 h every 4-wk. Bulls were castrated at one of six 4-wk intervals between 12 and 32 wk and blood samples were taken. Season of birth affected concentrations of testosterone (greater for spring-born) in intact bulls, but not luteinizing hormone (LH) or follicle stimulating hormone (FSH). The concentration of FSH increased about 30% between 4 and 32 wk, without evidence of pulsatile discharge. Basal concentration of LH was low and pulsatile discharges were infrequent at 4 or 8 wk. At 12, 16 and 20 wk, however, basal LH concentration was elevated and LH discharges were at less than 2-h intervals. Testosterone concentration did not rise until 18 to 20 wk, but then continued to rise; LH discharge was suppressed concomitantly. Bulls castrated at 16 or 20 wk had higher concentrations of LH in their blood both before and shortly after castration values for bulls, but by 21 d after castration values for bulls of all ages were similar. It was concluded that elimination of an unidentified suppressive factor allows frequent discharges of LH between 12 an 16 wk, but the testes do not respond by secreting more testosterone until 18 to 20 wk. By 24 wk, the testes are secreting more testosterone and pituitary production of LH is restored to a lower level; LH discharges decline in frequency and basal LH level declines. The high frequency discharges of LH between 12 and 20 wk are postulated to induce responsiveness of Leydig cells to LH and, thus, enable elevation of intratesticular testosterone to levels necessary for Sertoli cell differentiation and initiation of spermatogenesis.

R. P. Amann

Papers

Testicular Development and Establishment of Spermatogenesis in Holstein Bulls

The Male Rabbit. III. Determination of Daily Sperm Production by Means of Testicular Homogenates

Changes in the pituitary-gonadal axis associated with puberty in Holstein bulls.

The relationship of semen quality and fertility: a heterospermic study.

Comparisons of Computer Evaluations of Spermatozoal Motility with Standard Laboratory Tests and their use for Predicting Fertility