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Reproductive anatomy, physiology and endocrinology of bulls
No full textReproductive anatomy, physiology and endocrinology of bull
Testicular vascular cone development and its association with scrotal thermoregulation, semen quality and sperm production in bulls
No full textSeveral structural and functional features keep bull testes 2°C to 6°C below body temperature, essential for the production of morphologically normal, motile and fertile sperm. The testicular vascular cone (TVC), located above the testis, consists of a highly coiled testicular artery surrounded by a complex network of small veins (pampiniform plexus). The TVC functions as a countercurrent heat exchanger to transfer heat from the testicular artery to the testicular vein, cooling blood before it enters the testis. Bulls with increased TVC diameter or decreased distance between arterial and venous blood, have a greater percentage of morphologically normal sperm. Both the scrotum and testes are warmest at the origin of their blood supply (top of scrotum and bottom of testis), but they are cooler distal to that point. In situ, these opposing temperature gradients result in a nearly uniform testicular temperature (top to bottom), cooler than body temperature. The major source of testicular heat is blood flow, not testicular metabolism. High ambient temperatures have less deleterious effects on spermatogenesis in Bos indicus v. Bos taurus bulls; differences in TVC morphology in B. indicus bulls confer a better testicular blood supply and promote heat transfer. There is a long-standing paradigm that testes operate on the brink of hypoxia, increased testicular temperature does not increase blood flow, and the resulting hypoxia reduces morphologically normal and motile sperm following testicular hyperthermia. However, in recent studies in rams, either systemic hypoxia or increased testicular temperature increased testicular blood flow and there were sufficient increases in oxygen uptake to prevent tissue hypoxia. Therefore, effects of increased testicular temperature were attributed to testicular temperature per se and not to secondary hypoxia. There are many causes of increased testicular temperature, including high ambient temperatures, fever, increased recumbency, high-energy diets, or experimental insulation of the scrotum or the scrotal neck. It is well known that increased testicular temperatures have adverse effects on spermatogenesis. Heat affects all germ cells and all stages of spermatogenesis, with substantial increases in temperature and/or extended intervals of increased testicular temperature having the most profound effects. Increased testicular temperature has adverse effects on percentages of motile, live and morphologically normal sperm. In particular, increased testicular temperature increases the percentage of sperm with abnormal morphology, particularly head defects. Despite differences among bulls in the kind and percentage of abnormal sperm, the interval from increased testicular temperature to the emergence of specific sperm defects is consistent and predictable. Scrotal surface temperatures and structural characteristics of the testis and TVC can be assessed with IR thermography and ultrasonography, respectively
Content and activity of the testis-specific isoform of angiotensin-converting enzyme are reduced in frozen-thawed bull spermatozoa
No full textSperm cryopreservation and thawing reduces fertility and alters the content and function of various sperm proteins. Previously, we reported that a testes-specific isoform of angiotensin-converting enzyme (tACE) was required for capacitation of bovine spermatozoa. The aim of the present study was to determine effects of sperm cryopreservation and thawing on the content, activity and localisation of tACE in bovine spermatozoa. Relative median fluorescence intensity (flow cytometry) was greater (P<0.01), tACE content (110 kDa protein) in sperm proteins was higher (P<0.01) and there was greater tACE enzyme activity (mean (±s.e.m.) 0.16±0.01 vs 0.06±0.02UmL-1; P<0.01) in fresh versus frozen-thawed spermatozoa (n=6 bulls). In fresh spermatozoa, tACE was immunolocalised in the acrosomal and principal piece regions of the sperm head and tail respectively. However, in frozen-thawed spermatozoa, there were four patterns of localisation: most frozen-thawed spermatozoa (64%) had fluorescence in the acrosomal ridge, whereas in 17% and 9% of spermatozoa the signal was limited to the post-acrosomal region and the equatorial segment respectively; in the remainder (10%), there was no signal. We conclude that cryopreservation and thawing decrease the content and activity of tACE and cause it to be translocated to other parts of the sperm head
Effect of temperament and stress in the quality and fertility of bovine sperm.
No full textBovine fertility and sperm quality are complex processes, yet with a delicate balance that can be
impaired by different factor. An aspect not often considered is the temperament of the male. Bulls with more
aggressive behavior, tend to present worse breeding performances on the field. In addition, stress in a
general perspective, has strong impact on reproductive soundness of bulls. Exposure to heat stress (derived
from climatic changes and exposure to high temperature and humidity index), problems related to poor
management conditions during the animal handling, bad social interactions within the herd and
unbalanced diets and negative energy balance can also affect spermatogenesis and herd fertility.
Considering the economic and biological impact of fertility problems related to animal temperament and
stress, it is important to know the triggering factors of stressful conditions so that control and mitigation
measures can be implemented
Elevated anti-Müllerian hormone in stallions (Equus f. caballus) with teratoma and high inguinal testicle.
No full textThis report describes a stallion presenting a unilateral high inguinal undescended testicle and a unilateral scrotal testicle teratoma. Blood tests showed increased levels of anti-Müllerian hormone. Following castration, histological examination revealed that the teratoma contained testicular tissue, hair, hair bulbs, sebaceous glands, cartilage and endochondral bone. To our knowledge, this is the first study to report elevated anti-Müllerian hormone levels in a stallion with both a teratoma and a high-inguinal testicle
TESTICULAR MORPHOLOGY AND SEMEN CHARACTERISTICS OF FRESH AND THAWED SEMEN IN BEAUTY RAT SNAKES (ELAPHE TAENIURA): A MODEL FOR PHYSIOLOGY AND SPERM CRYOPRESERVATION OF ENDANGERED COLUBRIDAE.
No full textSnake populations are facing a significant global decline, with 33% of reptiles being classified as endangered [1]. Assisted reproductive technologies have proven to be fundamental to create gametes banks for species conservation [2, 3]. However, research on sperm collection, characteristics, and cryopreservation in snakes is notably scarce [3]. Beauty rat snakes (Elaphe taenuria) are classified as vulnerable, meaning that this species is considered at risk of extinction, unless the circumstances that are threatening their survival and reproduction change. Moreover, these snakes can serve as a model for assisted reproductive technologies in endangered species belonging to the family of Colubridae. For this reason, we aimed to investigate male anatomical features and sperm characteristics of 18 adult Beauty rat snakes. For each animal both testis and vasa deferentia were collected and measured for weight (testis) and length (testis and vasa deferentia). Furthermore, we assessed the effects of two distinct cryopreservation methods on sperm collected post-mortem. The spermatozoa were retrieved by and float up from vasa deferentia. Specifically, each vas deferens was placed into a 15 mL Falcon tube containing 1 mL of HEPES-TALP solution and incubated at room temperature (22 ◦ C) in the dark for 30 min. When retrieval and sperm analyses were successful (N = 11), spermatozoa were diluted into either a single or double-step TEST-yolk semen extender, with a final glycerol concentration of 12%. The freezing process took place at - 0.3°C/min in 0.5 mL straws, that were subsequently stored in liquid nitrogen for one week, when post-thaw sperm quality was assessed. Statistical analysis was performed using R version 4.3.1 (Vienna, Austria) and significance was considered for P < 0.05. Normally distribution of data was analyzed with Shapiro Wilk Test (P< 0.05). The Wilcoxon sum rank test indicated that the left testicle was smaller (45.77 mm ± 3 vs 51.39 mm ± 3.83; p = 0.007), lighter (1.18 g ± 0.25 vs 1.50 g ± 0.32; p = 0.003), and had a shorter vas deferens (271.94 mm ± 14.68 vs 332.39 mm ± 18.19; p = 0.0002) compared to the right one. However, no significant variations in total sperm count were observed in-between sides (p > 0.05). The total sperm count demonstrated a positive correlation between the number of morphologically normal spermatozoa and the weight of the testicle (p = 0.04 and p = 0.01, respectively; Spearman’s rank correlation test). There was no significant difference in terms of motility and morphology between the two freezing protocols (p > 0.05; Mann-Whitney U test). In conclusion, the present study describes some important andrological features of Beauty rat snakes, including new protocols for post-mortem sperm collection and cryopreservation. Furthermore, these results provide a starting point for studies on male reproductive physiology in Colubridae, not only for future research on this species but also as a model for endangered reptiles.
[1] IUCN. 2022. The IUCN Red List of Threatened Species. Version 2022-2. https://www.iucnredlist.org. Accessed on [November 30th, 2023].
[2] Huijsmans T.E.R.G. Postmortem Collection of Gametes for the Conservation of Endangered Mammals: A Review of the Current State-of-the-Art. Animals: an open access journal from MDPI, 13(8), 1360, 2023.
[3] Sandfoss M.R. Cryopreservation of Sperm from an Endangered Snake with Tests of Post-Thaw
Incubation in Caffeine. Animals: an open access journal from MDPI, 12(14), 1824, 2022
Ovarian and oocyte morphology during the spring-summer and fall-winterin Queens (Felis catus) kept in tropical climate
No full textThe objective of this study was to investigate the effects of seasonality and phase of the estrous cycle on ovarian and oocyte morphology in domestic cats kept in a tropical region. The ovaries from 23 queens were collected after elective ovariohysterectomy at different stages of the estrous cycle and were classified according to the season upon collection (spring/summer vs. fall/winter). Based on the findings, we concluded that queens in tropical regions experience no seasonal influence on oocyte quality, but there is a minimal effect on ovarian morphology, with an increase in ovarian length during proestrus/estrus in the spring/summer period
Heat stress impact on bovine female reproduction
No full textHeat stress (HS), a harmful condition affecting animal production, reproduction, and welfare, occurs when an animal is exposed to temperatures that exceed its thermal comfort zone. Several nonspecific body responses involving neural, neuroendocrine, and immune systems are triggered to keep homeostasis in such conditions. These responses, primarily directed to cooling the body, also impact the hypothalamic-pituitary-gonadal axis, compromising the bovine female’s release of gonadotropins. Heat stress also promotes reactive oxygen species accumulation in ovarian cells, impairing protein folding and refolding, triggering antioxidant and DNA protection mechanisms. These mechanisms, directed to reduce cell metabolism and increase survival chances, are not always sufficient to protect the cell and result in apoptosis. Heat stress’s systemic and cellular consequences impact ovarian estradiol production, estrous behaviors, follicular development, oocytes and embryo competence, conception rates, pregnancy establishment and maintenance, and even the future reproductive efficiency of the progenies of cows exposed to HS during pregnancy. The combat of heat stress includes strategies to alleviate the effect of progressive global warming, management strategies to cool the animals, reduced metabolic heat, and methane production dietary approaches. The use of reproductive biotechs and genetic strategies to increase thermotolerant animals are also critical to overcoming the harmful effect of HS
Testicular hypethermia increases blood flow that maintains aerobic metabolism in rams
No full textThere is a paradigm that testicular hyperthermia fails to increase testicular blood flow and that an ensuing hypoxia impairs spermatogenesis. However, in our previous studies, decreases in normal and motile spermatozoa after testicular warming were neither prevented by concurrent hyperoxia nor replicated by hypoxia. The objective of the present study was to determine the effects of increasing testicular temperature on testicular blood flow and O2 delivery and uptake and to detect evidence of anaerobic metabolism. Under general anaesthesia, the testicular temperature of nine crossbred rams was sequentially maintained at ~33°C, 37°C and 40°C (±0.5°C; 45min per temperature). As testicular temperature increased from 33°C to 40°C there were increases in testicular blood flow (13.2±2.7 vs 17.7±3.2mLmin-1 per 100g of testes, mean±s.e.m.; P<0.05), O2 extraction (31.2±5.0 vs 47.3±3.1%; P<0.0001) and O2 consumption (0.35±0.04 vs 0.64±0.06mLmin-1 per 100g of testes; P<0.0001). There was no evidence of anaerobic metabolism, based on a lack of change in lactate, pH, HCO3- and base excess. In conclusion, these data challenge the paradigm regarding scrotal-testicular thermoregulation, as acute testicular hyperthermia increased blood flow and tended to increase O2 delivery and uptake, with no indication of hypoxia or anaerobic metabolism
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