Testicular mitosis, meiosis and apoptosis in mink (Mustela vison) during breeding and non-breeding seasons

Testes of mink were compared between the breeding (March) and non-breeding seasons with the start (November) and cessation (May) of spermatogenic activity. Testicular mass and spermatozoa per gram testis were assessed. Percentages of haploid (1C), diploid (2C) and tetraploid (4C) cells were monitored using DNA flow cytometry and the proportions of somatic and spermatogenetic cells were determined after selective labelling of somatic cells with a vimentin antibody. Apoptosis was examined by cell death detection ELISA, and testosterone concentrations were measured with an enzyme-immunoassay. The significantly higher testis mass during the breeding period coincided with higher numbers of testicular spermatozoa per gram testis and peak of testicular testosterone concentration in comparison with non-breeding periods. The proportions of 1C, 2C and 4C cells showed corresponding strong differences between these periods with the maximum of 1C cells during breeding. The proportions of testicular cells in G2-M phase of mitosis were very low during the period of peak spermatogenesis; they were markedly increased in the time of autumnal resumption in November but were even higher during testis involution in May. However. the meiotic transformation (1C:4C ratio) is maximal in March. The total as well as the relative proportions of spermatogenic and somatic cells differed significantly not only between breeding and non-breeding periods but also between the periods at the start and at the end of active spermatogenesis. The intensity of apoptosis was also seasonally dependent. The highest level in March indicates a stimulated apoptosis even during the breeding period. In conclusion, the production of spermatozoa in mink is intensified by enlargement of gonads as well as enhanced efficiency of spermatogenesis during breeding. In this time, the testosterone concentration and the meiotic transformation show high levels, but the mitotic activity of spermatogenic cells is already significantly diminished and an intensified apoptosis seems to precede the forthcoming testis involution after breeding. The results suggest that the regulation of seasonal testicular activity is characterised by co-ordinated shifts in the relationships between mitosis, meiosis, apoptosis and testosterone production.     

Seasonal changes in spermatogenesis in the blue fox (Alopex lagopus), quantified by DNA flow cytometry and measurement of soluble Mn2+ -dependent adenylate cyclase activity

The testes of the blue fox (Alopex lagopus) showed marked seasonal variations in size. Testicular weight and volume increased rapidly during January and February to reach maximal values by the beginning of the breeding season (approximately 15 March). During May and June the weights and volumes of the testes declined gradually to the quiescent state which lasted from July until October. Quantitation by DNA flow cytometry of the seasonal changes in the relative numbers of haploid (1C), diploid (2C) and tetraploid (4C) cell numbers in the testis showed that the increase in testis size from December to February was associated with a rapid expansion of the haploid cell compartment as spermatogenesis resumed. In addition, an increase in number of more mature cell types within the haploid cell population was observed over a 2-month period before the breeding season. The decline in testicular size from the middle of April until October was associated with a reduction in both the absolute and relative sizes of the haploid and tetraploid cell populations and a concomitant increase in the relative numbers of diploid cells. Measurements of the activity of the soluble Mn2+ -dependent adenylate cyclase revealed seasonal variations that closely paralleled those of the haploid cell population, indicating that, as in other species, the enzyme may be associated with maturing germ cells.     

Seasonal variation in serum testosterone, testicular volume and semen characteristics in coatis (Nasua nasua)

The objective was to characterize seasonal changes in serum testosterone concentration, testicular volume and sperm quantity and quality in captive coatis (Nasua nasua) from Pantanal, MT, Brazil. Sampling was done once monthly for 1 y. Mean (± SEM) serum testosterone concentrations (767.37 ± 216.2 ng/ml) and total and progressive sperm motility (79.6 ± 3.9%; 3.8 ± 0.3, on a scale of 0 to 5) peaked in July. The highest combined testis volume (10.3 ± 0.4 cm³) and sperm concentration (403 million ± 102 sperm/ml) occurred in August, at the peak of the winter breeding season. No seasonal effects on percentages of morphologically normal sperm, acrosome integrity, or live sperm were detected; however, the percentage of secondary sperm defects was higher in the winter. In conclusion, intricate relationships between testosterone concentration, testis volume, semen concentration and total and progressive sperm motility with high levels of breeding activity were observed during the dry season in the winter (June, July, August), followed by a subsequent decline in these activities during the wet season (i.e., summer: December, January, February). There was no seasonal pattern for production of functionally intact and morphologically normal sperm.     

Testosterone production and spermatogenesis in free-ranging Eurasian lynx (Lynx lynx) throughout the year

Seasonal variation in reproduction is common in mammals as an adaptation to annual changes in the habitat. In lynx, male reproduction activity is of special interest because female lynxes are monoestric with an unusual narrow (about 1 month) breeding season. In Eurasian lynx, mating occurs between January and April depending on the latitude. To characterize the seasonal pattern of sperm and testosterone production in free-ranging Eurasian lynxes, long-term frozen-stored testis material obtained postmortem from 74 hunted or road-killed lynxes in Sweden was used to analyze annual changes in testis mass, testicular testosterone content, and spermatogenetic activity. Values of most gonadal parameters obtained in subadult lynxes were significantly different from the values observed in adult males. In adult lynxes, a moderate annual fluctuation of gonadal parameters was found which was most profound for testis weight and testicular testosterone concentration reaching highest values in March (median of 2.18 g and 2.67 μg/g tissue respectively). Grouping the data of pre-/breeding (January–April) and postbreeding season (May–September) revealed significant changes in testis weight and testosterone concentration. The relative spermatogenetic activity remained high in postbreeding testes. However, net sperm production decreased according to reduction of testis mass and a tendency to lower cauda epididymal sperm numbers in the postbreeding period was observed. Our results demonstrate that it is possible to analyze the gonadal activity of frozen testis/epididymis tissue postmortem and that male Eurasian lynxes show—opposite to the females—only moderate seasonal changes in their reproductive capacity.     

Relationship of intratesticular testosterone content of stallions to age, spermatogenesis, Sertoli cell distribution and germ cell-Sertoli cell ratios

Testes were obtained from 47 1-20-year-old stallions during the natural breeding season. Total testicular testosterone and testosterone/g testis increased with age (P less than 0.005), and total testicular testosterone was associated with larger testis size (P less than 0.05). Neither testosterone per gram nor per paired testes were related to total Sertoli cell number (P greater than 0.05), but greater testosterone per paired testes was associated with fewer Sertoli cells per unit of seminiferous tubule length (P less than 0.005) or basement membrane area (P less than 0.02) and with a higher number of germ cells supported per Sertoli cell (P less than 0.05). Although values for testosterone per gram and per paired testes were unrelated (P greater than 0.10) to sperm production/g testis or to the yield of spermatids/spermatogonium, testosterone per paired testes was positively related to sperm production per paired testes (P less than 0.05). It is concluded that intratesticular testosterone increases with age, is related in a positive manner to quantitative rates of sperm production, and can account for some of the differences in sperm production among individual stallions within a single breeding season.     

Seasonal timing of sperm production in roe deer: interrelationship among changes in ejaculate parameters,morphology and function of testis and accessory glands

Roe deer are seasonal breeders with a short rutting season from mid-July to mid-August. The seasonality of reproductive activity in males is associated with cyclic changes between growth and involution of both testes and the accessory sex glands. This study characterizes morphological and functional parameters of these organs prior to, during and after breeding season in live adult roe deer bucks. Size and morphology of the reproductive tract was monitored monthly by transcutaneous (testes, epididymis) and transrectal (accessory glands) ultrasonography. Semen was collected by electroejaculation. Concentration, motility and morphological integrity of spermatozoa as well as the content of proteins and testosterone in semen plasma were evaluated. Proportions of haploid, diploid and tetraploid cells were estimated by flow cytometry in testicular tissue biopsies. Serum testosterone was measured by enzyme immunoassay. Most parts of the male reproductive tract showed distinct circannual changes in size and texture. These changes were most pronounced in the testes, seminal vesicles, and prostate. All reproductive organs were highly developed during the rut only. The volume of ejaculates, total sperm number and percentages of motile and intact spermatozoa also showed a maximum during this period and corresponded with high proportions of haploid cells in the testis. The highest percentages of tetraploid cells were found in the prerutting period. The production of motile and intact spermatozoa correlated with both the protein content of semen plasma and the concentration of testosterone in semen plasma and blood serum. These results suggest the importance of combined actions of the testes and accessory sex glands and the crucial role of testosterone in facilitating the optimal timing of intensified semen production to ensure sufficient numbers of normal spermatozoa in seasonal breeders.     

Inverse relationship between testicular proliferation and apoptosis in mammalian seasonal breeders

Seasonal cycles of testicular activity occur in many mammals and can include transitions between total arrest and recrudescence of spermatogenesis. We hypothesize that involution and reactivation of testis result from two antagonistic processes, proliferation and programmed cell death (apoptosis), which are activated at different times. To test this hypothesis, quantitative measurements of both proliferation-specific marker and apoptotic produced nucleosomes have been compared with sperm and testosterone production in testes from adult roe deer during breeding and non-breeding seasons (May to September). Testes of brown hare were included from periods of testes regression (June to August) and recrudescence (November to December). The highest testicular weights in roe deer were found in the rutting period from late July to early August (27.25 +/- 8.56 g), corresponding with the highest number of testicular sperm/g parenchyma. The peak of sperm production coincided with a peak in testosterone concentration (1.19 +/- 0.53 microg/g testis). The maximum level of proliferation-specific marker was also found during the breeding season (98.6 +/- 58.2 U/g testis in comparison to 20.1 +/- 22.0 U/g in the prerutting period). In contrast, the most significant apoptosis was observed in the nonbreeding season than the breeding period (71.11 +/- 5.79 U/mg testis and 18.88 +/- 6.79 U/mg, respectively). Testicular proliferation was low in the brown hare (0.061 +/- 0.062 U/g) during involution of the testes. It was newly activated in November and December (0.85 +/- 0.33 U/g), preceding the increase in testicular volume. Testosterone production increased in conjunction with testicular proliferation. At this time, testicular apoptosis was significantly lower (14.16 +/- 2.12 U/mg testis) than during the period of pronounced testicular regression (30.16 +/- 19.95 U/g). These results suggest that regulation of seasonal testicular activity is characterized by an inverse relationship of proliferation and apoptosis.     

Seasonal variation in serum testosterone, testicular volume, and semen characteristics in the coyote (Canis latrans)

The coyote is a seasonally breeding mammal, with most copulations occurring between December and April (depending on location). The objective of this study was to characterize seasonal changes in serum testosterone concentrations, testicular volume, and ejaculate quantity and quality in captive male coyotes. There were seasonal differences in testicular volume, with the greatest volume (20.2+/-5.4cm2), mean+/-S.E.M.) in February, corresponding with peak breeding season. Circulating serum testosterone concentrations peaked (3.31+/-0.9 ng/mL) during January and were positively correlated (P< or =0.001, r=0.413) with testicular volume. Ejaculate volume (1.67+/-0.4 mL) and sperm concentration (549.2 x 10(6)+/-297.7 spermatozoa/mL) both peaked during January and February, consistent with the height of the breeding season. Ejaculate volume and sperm concentrations were positively correlated with testicular size (r=0.679, P< or =0.001 and r=0.499, P< or =0.001, respectively) and with serum testosterone concentrations (r=0.368, P< or =0.01 and r=0.208, P< or =0.05). Progressively motile, viable, and morphologically normal spermatozoa fluctuated seasonally, peaked (90.4+/-4.5, 84.8+/-4.1, and 87.9+/-2.9%) during the breeding season, and then subsequently declined (period of aspermatogenesis). All three of these end points were positively correlated with testicular size (r=0.589, P< or =0.001; r=0.586, P< or =0.001; and r=0.469; P< or =0.001) and serum testosterone (r=0.167, P< or =0.05; r=0.190, P< or =0.05; and r=0.221, P< or =0.01). In conclusion, there were intricate relationships among testosterone concentrations, testicular volume, and the production of both functionally intact and morphologically normal spermatozoa.     

Beyond Testis Size: Links between Spermatogenesis and Sperm Traits in a Seasonal Breeding Mammal

Spermatogenesis is a costly process that is expected to be under selection to maximise sperm quantity and quality. Testis size is often regarded as a proxy measure of sperm investment, implicitly overlooking the quantitative assessment of spermatogenesis. An enhanced understanding of testicular function, beyond testis size, may reveal further sexual traits involved in sperm quantity and quality. Here, we first estimated the inter-male variation in testicular function and sperm traits in red deer across the breeding and non-breeding seasons. Then, we analysed the relationships between the testis mass, eight parameters of spermatogenic function, and seven parameters of sperm quality. Our findings revealed that the Sertoli cell number and function parameters vary greatly between red deer males, and that spermatogenic activity co-varies with testis mass and sperm quality across the breeding and non-breeding seasons. For the first time in a seasonal breeder, we found that not only is the Sertoli cell number important in determining testis mass (r = 0.619, p = 0.007 and r = 0.248, p = 0.047 for the Sertoli cell number assessed by histology and cytology, respectively), but also sperm function (r = 0.703, p = 0.002 and r = 0.328, p = 0.012 for the Sertoli cell number assessed by histology and cytology, respectively). Testicular histology also revealed that a high Sertoli cell number per tubular cross-section is associated with high sperm production (r = 0.600, p = 0.009). Sperm production and function were also positively correlated (r = 0.384, p = 0.004), suggesting that these traits co-vary to maximise sperm fertilisation ability in red deer. In conclusion, our findings contribute to the understanding of the dynamics of spermatogenesis, and reveal new insights into the role of testicular function and the Sertoli cell number on testis size and sperm quality in red deer.     

Spatial and Temporal Changes in Testis Morphology and Sperm Ultrastructure of the Sportfish Sauger (Sander canadensis)

The objective of this study was to assess testicular morphology and spermatozoal structure spatially within the reproductive tract and temporally among seasons in the sauger (Sander canadensis). The testis exists as two separate lobes joined at the urogenital pore and were characterised as unrestricted lobular with seminiferous tubules terminating at the ventral periphery and coalescing dorsally on the main sperm duct. Differences were observed between the pre-breeding season (November) and breeding season (March), with every stage of spermatogenesis occurring in spermatocysts in pre-breeding season in contrast to only spermatozoa being present in the tubules and main duct during the breeding season. Longitudinal folds in the main duct epithelium increased in number with increasing proximity to the urogenital pore, greatly increasing epithelial height regardless of season. Sauger spermatozoa consisted of an ovoid head, a midpiece containing 2 – 4 mitochondria incorporated into the head and a single flagellum containing an asymmetrical lateral ribbon. Motile spermatozoa were found throughout the testis during the breeding season. A decrease in sperm concentration was quantified moving proximally, suggesting a hydration effect by the main duct epithelium during the breeding season. These observations fill an important knowledge gap regarding reproductive biology of this impactful recreational fish species.     

Increased germ cell degeneration and reduced germ cell:Sertoli cell ratio in stallions with low sperm production

To determine the relationship between germ cell degeneration or germ cell:Sertoli cell ratio and daily sperm production, testes were obtained during the months of May to July (breeding season) and November to January (nonbreeding season) from adult (4 to 20-yr-old) stallions with either high (n = 15) or low (n = 15) sperm production. Serum was assayed for concentrations of LH, FSH and testosterone. Testes were assayed for testosterone content and for the number of elongated spermatids, after which parenchymal samples were prepared for histologic assessment. Using morphometric procedures, the types and numbers of spermatogonia, germ cells and Sertoli cells were determined. High sperm producing stallions had greater serum testosterone concentration, total intratesticular testosterone content, testicular parenchymal weight, seminiferous epithelial height, diameter of seminiferous tubules, numbers of A and B spermatogonia per testis, number of Sertoli cells per testis, and number of B spermatogonia, late primary spermatocytes, round spermatids and elongated spermatids per Sertoli cell than low sperm producing stallions (P < 0.05). The number of germ cells (total number of all spermatocytes and spermatids in Stage VIII tubules) accommodated by Sertoli cells was reduced in low sperm producing stallions (18.6 +/- 1.3 germ cells/Sertoli cell) compared with that of high sperm producing stallions (25.4 +/- 1.3 germ cells/Sertoli cell; P < 0.001). The conversion from (yield between) early to late primary spermatocytes and round to elongated spermatids was less efficient for the low sperm producing stallions (P < 0.05). Increased germ cell degeneration during early meiosis and spermiogenesis and reduced germ cell:Sertoli cell ratio was associated with low daily sperm production. These findings can be explained either by a compromised ability of the Sertoli cells to support germ cell division and/or maturation or the presence of defects in germ cells that predisposed them to degeneration.     

Mating-associated peak in plasma testosterone concentration in wild male grey-headed flying foxes (Pteropus poliocephalus)

Plasma testosterone (T) concentrations, measured in wild bats of P. poliocephalus in Queensland in 1983-87, showed a peak during the mating season in March. Plasma androstenedione (A) concentrations changed less dramatically with season. Mean testicular concentration and total content of T and A was substantially greater in March than in regressed testes in July-October. Paired adrenal glands were heavier during February to April than during September to November. In the same wild population, throughout a single breeding season (1987), plasma T concentrations were significantly higher in mid-March than 3 weeks previously or 3 weeks later. Testicular T content rose as the breeding season progressed, being greatest during March, coinciding with the large rise in plasma T concentrations. Testicular T concentration and content were correlated significantly with plasma T concentrations. Adrenal glands contained T, but the absolute concentrations were much lower than in the testis. No significant changes in plasma, testicular or adrenal A concentrations were found as the breeding season progressed. The large increase in plasma T during the mating season appears to be due to increased testicular production.     

Investigations on reproductive physiology in the male Eurasian lynx (Lynx lynx)

This study characterized (in vivo) morphological and functional parameters of reproductive organs of adult male lynx (n = 3) prior to, during, and after the breeding season (n = 3). Size and morphology of the reproductive tract were monitored by transcutaneous (testes) and transrectal (accessory sex glands) ultrasonography. Semen was collected by electroejaculation. Ejaculate volume, sperm number, motility, and morphology of spermatozoa as well as testosterone concentrations in blood serum and feces were evaluated. The testes and prostate had seasonal changes in size and echotexture. The mean (+/- S.D.) maximum and minimum testicular volume were 2.8 +/- 0.8 cm3 and 1.5 +/- 0.3 cm3, respectively. Fecal testosterone concentrations were highest in February (1240 +/- 393 ng/g feces), with a second increase in May (971 +/- 202 ng/g feces), but concentrations were lowest in January (481 +/- 52.9 ng/g feces). Ejaculate volume, total sperm number and percentage of motile, and intact spermatozoa were maximal in March (the middle of the breeding season). In one of the eight litters, multiple paternity was proven; however, in the remaining seven litters, all 16 cubs were sired by the same male. This particular male had the most developed and active testes and best semen quality, which may be important for sperm competition.     

Morphometric studies on mink testicular tissue

The mink, a seasonal breeder of great economic importance, shows a high incidence of male infertility. This problem has forced investigators to find methods of assaying male mink infertility. In this study, morphometric studies have been performed on testicular tissue of a total of 31 males eliminated from breeding after testicular palpation, sperm test, and estimation of serum testosterone concentrations. Males having low sperm quality or disturbed testicular development (n=24) had significantly (p<0.01) lower numbers of spermatocytes, spermatids, and freefloating luminal spermatozoa. compared with males with good sperm quality (n=7). No differences were found in the numbers of spermatogonia, Sertoli, and Leydig cells. Other morphometric parameters such as mean diameter, mean area, mean volume, percentage of area, and surface area per volume of nuclei are also presented for each cell type in the testis. It may be concluded that the sperm test is best suited for assessing fertility in mink. Severe disturbances in testicular development can be detected by testicular palpation and serum testosterone measurements.     

Annual changes in testicular development and plasma sex steroids in the captive male dojo loach <Emphasis Type="Italic">Misgurnus anguillicaudatus</Emphasis>

Testicular development in the captive male dojo loach Misgurnus anguillicaudatus was examined monthly in relation to the levels of plasma sex steroids [testosterone (T), 11-ketotestostrone (11-KT), and 17,20β-dihydroxy-4-pregnen-3-one (DHP)]. On the basis of testicular histology, the annual gonadal cycle was found to be divisible into 3 periods: the recovery and proliferation period, which mainly consists of early spermatogenic testis from August to November (reproductive phase I); the preparation period for the next spawning period, which mainly consists of late spermatogenic testis from December to April (reproductive phase II); and the mature period, characterized by a high proportion of mature testis from May to July (reproductive phase III). Individual variability in testicular development was high, and continuous spermatogenesis was observed throughout the year. High levels of plasma T, 11-KT, and DHP were observed during reproductive phase III. 11-KT began to increase in February, while T was present at low levels in reproductive phase II. These results suggest that the physiologically active season of testis development for breeding in the dojo loach is from May to July, although spermatogenesis occurs throughout the year.     

Age-related and seasonal variation in the Sertoli cell population, daily sperm production and serum concentrations of follicle-stimulating hormone, luteinizing hormone and testosterone in stallions

Testes and blood samples were obtained from 201 stallions aged 6 months to 20 years in either December-January (nonbreeding season) or June-July (breeding season) to study the effect of age and season on reproductive parameters. Seasonal differences in the Sertoli cell population of adult (4-20 years old) horses were characterized by a 36% larger number of Sertoli cells in the breeding season than in the nonbreeding season. Seasonal elevation in the Sertoli cell population was associated with an increase in testicular weight and daily sperm production per testis (DSP/testis). Concentrations of luteinizing hormone (LH) and testosterone in serum varied with season. Although follicle-stimulating hormone (FSH) concentrations also tended to be higher in the breeding season, this trend was not statistically significant (P less than 0.08). Sertoli cell numbers averaged over both seasons, like testicular weights, increased with age until 4-5 years of age, but were stabilized thereafter. This age-related difference was also associated with increased concentrations of FSH, LH and testosterone, and with increased DSP/testis. The Sertoli cell population was capable of increasing in the adult horse by fluctuating its size with season. The number of elongated spermatids per Sertoli cell over both seasons increased with age up to 4-5 years of age and was stabilized thereafter. Thus, seasonal and/or age-related differences in DSP/testis were associated with significant elevations in serum concentrations of FSH, LH and testosterone, testicular weights, numbers of elongated spermatids per Sertoli cell and elevation of the Sertoli cell population.     

Apoptosis is not the cause of seasonal testicular involution in roe deer

Apoptosis is involved in the regulation of spermatogenesis. The involution of testes in seasonal breeders might be expected to involve enhanced apoptotic cell elimination. We have compared seasonally changing testicular apoptosis in roe deer with that in non-seasonally breeding cattle. Apoptotic cells were detected as TUNEL-positive cells by both flow-cytometric analysis and in situ localisation of fragmented DNA in tissue sections. Apoptosis-induced DNA fragments were also assessed by enzyme-linked immunosorbent assay (ELISA) in homogenised testicular parenchyma. As expected, the testis mass and the percentage of haploid cells in roe deer showed a seasonal pattern with a significant maximum during the rut (August), whereas no annual variation of these parameters was found in bulls. All three methods for determining apoptosis showed similar findings. Roe deer exhibited significant seasonal fluctuation of total apoptotic activity (ELISA, apoptotic cells per tubule cross section) with a maximum during the breeding season. However, the seasonal differences in the number of apoptotic cells corresponded to the variable total numbers of spermatogonia and spermatocytes per tubule cross section. Thus, the percentages of TUNEL-positive cells related to the combined number of both germ cell types showed no seasonal variance, as confirmed by percentages of apoptotic cells analysed flow-cytometrically. The maximum level of apoptosis during the rut in roe deer was similar to the values obtained during the invariably high spermatogenic activity in cattle. These results suggest that, in roe deer, apoptosis is not the cause of the seasonal involution of testes. This study was partially supported by grant Bl 319/6-1 from the Deutsche Forschungsgemeinschaft.     

Characterization of reproductive activity in captive male Eurasian lynx (Lynx lynx)

This study characterizes the reproductive activity of male European lynx kept in Central Russia. Four captive adult males were subjected to an electroejaculation prior to (November), during (March) and after (June) the breeding season. Concentration, motility and morphological integrity of spermatozoa as well as testis diameter and testosterone levels in serum were evaluated. Additionally, fecal samples were collected for 2 years to determine the fecal testosterone secretion. Testis sizes and serum testosterone concentrations were characterized by little changes with highest levels in March (2.98 mm³; 1.96 ng/ml testosterone) and lowest in June (2.34 mm³; 0.75 ng/ml testosterone). In faeces, the highest testosterone concentrations were measured in February followed by a second increase in May. The volume of ejaculates and percentages of motile and intact spermatozoa reached the maxima in March. By performing two-male mating experiments, we could prove multiple paternity within three litters. Paternity analysis of litter also revealed that 26 of 31 cubs (84%) were sired from the same male, independently from being the first or second mating partner of the respective female. This particular male showed the most developed and activated reproductive tract and also had the best semen quality, which seems to be important for sperm competition.     

Seasonal variation in pituitary-gonadal function in free-ranging impala (Aepyceros melampus).

Blood, testicular biopsies and electroejaculates were collected from adult male impala, free-ranging in the Kruger National Park (Republic of South Africa), during the breeding (rut; April-May) and nonbreeding (September-October) seasons. Blood samples were collected at 5-min intervals for 120 min from anaesthetized males (n = 7 impala/group) treated intravenously with saline, gonadotrophin-releasing hormone (GnRH: 1 microgram/kg body weight) or human chorionic gonadotrophin (hCG: 10 or 30 iu/kg). Semen was collected from six more animals during the breeding season and 12 animals during the nonbreeding season using a standardized electroejaculation protocol. Ejaculates obtained during the nonbreeding season were of inferior quality to those collected during the breeding season, and were characterized by lower sperm concentrations, poorer sperm motility and more morphologically abnormal sperm forms. Within season, there were no differences in testosterone secretion between the two hCG doses, and these responses were similar to those observed after GnRH, but during the rut, testosterone secretion stimulated by both GnRH and hCG was approximately nine times greater than during the nonbreeding season. This seasonal increase in testosterone production was associated with a doubling in testicular volume and concentrations of luteinizing hormone (LH) receptors. Although concentrations of testicular follicle-stimulating hormone (FSH) receptors were similar between seasons, receptor content increased during rut as a result of increased testicular volume. In contrast to testosterone secretion, basal LH and FSH secretions were unaffected by season and GnRH-induced gonadotrophin secretion was reduced during rut.(ABSTRACT TRUNCATED AT 250 WORDS)     

Spermatogenesis, testicular composition and the concentration of testosterone in the equine testis as influenced by season

The influence of season on spermatogenesis, testicular composition and the concentration of testosterone in the equine testis was evaluated using testes from 45 stallions. Testes were obtained through a commercial abbatoir during September, December-January, March and July. The weights of the testes, the tunica albuginea and testicular parenchyma and the proportion of the testicular parenchyma occupied by seminiferous tubules or interstitial tissue were similar during each season. How ever, diameter of the seminiferous tubules was greater in July than during other months of the study. In addition, the concentration of testosterone within the testicular parenchyma was twice as great during July as during the fall and winter, and this period of peak testicular testosterone concentrations was associated with spermatozoal production rates, which were 65% greater than those observed in September.