Seasonal Changes in Serum Testosterone, LDH Concentration and Semen Characteristics in Markhoz Goats

The role of GnRH in Tibetan male sheep and goat reproduction

The hypothalamic-pituitary-gonadal (HPG) axis connects the hypothalamus, pituitary gland, and gonads. The regulation of reproductive processes includes integrating various factors from structural functions and environmental conditions in the HPG axis, with the outcome indication of these processes being the pulsatile secretion of gonadotropin-releasing hormone (GnRH) from the hypothalamus. These factors include feed consumption and nutritional condition, sex steroids, season/photoperiod, pheromones, age, and stress. GnRH pulsatile secretion affects the pattern of gonadotropin secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which then regulates both endocrine function and gamete maturation in the gonads. This regulates gonadotropins and testosterone (T) production. There is evidence that in males, GnRH participates in a variety of host behavioural and physiological processes such as the release of reproductive hormones, progression of spermatogenesis and sperm function, aggressive behaviour, and physiological metabolism. GnRH activates receptors expressed on Leydig cells and Sertoli cells, respectively to stimulate T secretion and spermatogenesis in the testis. Photoperiod affects the reproductive system of the hypothalamic-pituitary axis via rhythmic diurnal melatonin secretion. Increased release of melatonin promotes sexual activity, GnRH production, LH stimulation, and T production. This induces testicular functions, spermatogenesis, and puberty. GnRH reduces the release of LH by the pituitary through the cascade effect and decreases plasma concentration of T. Gut microbiota maintain sex steroid homeostasis and may induce reduction in reproduction productivity. Recently, findings of kisspeptin-neurokinin-dynorphin neuronal network in the brain have resulted in fast advances in how GnRH secretion is controlled. Emerging studies have also indicated that other neuropeptide analogues could be used in control reproduction procedures in various goat and sheep breeds. The Tibetan male sheep and goats reproduce on a seasonal basis and have high reproductive performance. This is a review for the role of GnRH in Tibetan male sheep and goats reproduction. This is intended to enhance reproductive knowledge for understanding the key roles of GnRH relating to male reproductive efficiency of Tibetan sheep or goats.

New insight into copy number variations of goat SMAD2 gene and their associations with litter size and semen quality

Copy number variations (CNV) contribute significantly to genetic variations. Numerous studies have shown that CNV affects phenotypic traits in livestock. The SMAD family member 2 (SMAD2) is a leading candidate gene in reproduction and has a crucial effect on litter size. Additionally, SMAD2 is also required for male reproduction and influences male germ cell development. However, there are no reports on investigating the effect of CNVs in the SMAD2 gene on reproductive traits in goat. Therefore, the goal of this study was to explore associations between CNV of the SMAD2 gene and litter size and semen quality in Shaanbei white cashmere (SBWC) goats. In this study, two CNVs within the SMAD2 were identified in 352 SBWC goats (50 males and 302 females). The association analysis revealed that only CNV2 was significantly associated with female goat first-born litter size (P = 3.59 × 10^-4), male semen concentration (P < 0.01), ejaculation volume, live sperm count, and sperm deformity rate (P < 0.05). In terms of phenotypic performance, the individuals with loss genotypes outperformed those with other genotypes. CNV1 and CNV2 genotype combinations containing their dominant genotypes were also associated with goat litter size (P = 1.7 × 10^-5), but no differences in semen quality were found. In summary, CNV2 of the SMAD2 gene is useful for molecular marker-assisted selection breeding, as it is associated with essential goat reproductive traits.

Seasonal changes in testis size, testosterone levels and sperm production quality in meat rams

The aim of the present study was to evaluate seasonal changes in testes size, serum testosterone (T) levels and sperm production characteristics of 24 adult (2-3 years old) rams of meat breeds: Charollais (n = 6), Ile de France (n = 6), Dorset (Polled) (n = 5) and Dorper (Dorper, n = 7). Semen was collected with artificial vagina using a female in spontaneous oestrus (September-November, breeding season, BS) or a female with induced oestrus (March-July, non-breeding season, NBS). A total of 672 ejaculates were examined. Jugular vein blood was collected to determine testosterone levels during BS and NBS, and serum was extracted. Results of the present study indicate that there was no significant change in parameters such as body weight (kg) and testes length, both right and left, during BS and NBS, irrespective of the breed. The remaining metrics of testes differ in varying degrees between breeds of rams (with the exception of the Dorper breed) between BS and NBS. No significant variation in these parameters was found in Dorper rams. For all breeds, season had a statistically significant effect on important parameters such as total sperm count and progressive sperm motility after thawing. There was also significant seasonal variation in ejaculate volume across the three breeds, excluding il-de-France rams. The most constant was the sperm concentration, which was unchanged in BS and NBS in the three breeds, excluding Dorset rams, which showed a slightly significant decrease in this indicator in the non-breeding season. The serum content of the major male hormone testosterone (T) in rams of all breeds showed significant changes between BS and NBS, decreasing by a highly significant amount in the non-breeding season.

In vitro supplementation of testosterone or prolactin affects spermatozoa freezability in small ruminants

In small ruminants, testosterone and prolactin plasma concentrations show circannual fluctuations as an adaptation mechanism to their seasonal breeding behavior. Sperm resistance to the freezing-thawing process shows seasonal fluctuation throughout the year, with lower sperm freezability at the beginning of the breeding season when prolactin and testosterone levels reach their maximum concentration. Nevertheless, whether these hormones directly affect post-thaw sperm quality parameters is still unclear. The objective was to study the effect of testosterone or prolactin added in vitro on sperm freezability in domestic ram (Ovis aries) and buck (Capra hircus). Sperm samples were incubated for 1 h with a range of testosterone (0, 2, 4, or 6 ng/mL; Exp. 1) or prolactin (0, 20, 100, 200, or 400 ng/mL; Exp. 2) concentrations. Samples were cryopreserved by slow freezing in straws at 0 h and after 1 h incubation. Sperm viability, acrosome integrity, motility, and kinetic parameters were assessed at 0 and 1 h in fresh and frozen-thawed samples. Results showed no hormone effect in fresh sperm, whereas these hormones affected post-thaw sperm parameters. In Exp. 1, in vitro incubation with testosterone decreased the post-thaw acrosome integrity of ram sperm (from 68.1 ± 6.3% to 49.6 ± 3.9%; P < 0.05). In Exp. 2, in vitro incubation with prolactin decreased the post-thaw acrosome integrity of ram (from 78.2 ± 3.4% to 66.3 ± 3.5%; P < 0.05) and buck sperm (from 81.7 ± 2.5% to 67.6 ± 3.5%; P < 0.05). Moreover, prolactin increased the post-thaw amplitude of lateral head displacement in ram sperm (from 3.3 ± 0.1 μm to 3.8 ± 0.2 μm; P < 0.05). In conclusion, either testosterone or prolactin added in vitro decreased the post-thaw acrosome integrity of ram and buck sperm. This suggests a destabilization process that could be decreasing sperm freezability when physiological levels of these hormones are high in vivo.

Effects of letrozole administration on growth and reproductive performance in Markhoz goat bucklings

This study evaluated the growth performance, testicular and semen characteristics, and hormonal profile of Markhoz (Iranian Angora) bucklings injected with letrozole (LTZ). Twenty-eight 4-4.5 month old bucks were randomly assigned into four groups and received either 0.25 mg/kg body weight (BW) LTZ subcutaneously (sc LTZ) or intramuscularly (im LTZ), and also sc (sc CONT) or im (im CONT) controls every week for 3 months. The study was performed at the beginning of the breeding season in Sanandaj Animal Husbandry Research Station (46.99 °E, 35.31 °N). The results showed that LTZ causes increased final body weight (25.78 ± 1.61 kg), higher average daily gain (104 ± 0.03 g/days), and decreased feed conversion ratio (7.81 ± 2.57) (P < 0.05). The pre-slaughter, hot, and cold carcass weights (27.56 ± 2.40, 11.45 ± 1.07 and 11.11 ± 1.05 kg, respectively) were (P < 0.05) heavier in LTZ groups while other carcass characteristics did not differ between groups. No differences occurred between the groups in biochemical parameters, except high-density lipoprotein levels (35.47 ± 2.43 mg/dL) which was higher in LTZ treatments (P < 0.05). LTZ-treated bucks had larger scrotal circumference (20.12 ± 5.75 cm), higher relative testicular weight (560.91 ± 78.59 mg/100 g BW) and volume (175.5 ± 29.71 cm³), greater diameter of seminiferous tubules (224.5 ± 5.21 μm), and number of Sertoli cells (8.39 ± 0.77) (P < 0.05). Semen volume (0.74 ± 0.16 mL), sperm concentration (2.64 ± 0.19 × 10^-9/mL), total sperm per ejaculate (1.95 ± 0.49 × 10^-9), and semen index (1248 ± 323) increased (P < 0.05) by LTZ treatments, while semen pH (6.77), motility (80.91%), progressive motility (76.75%), viability (83.35%), abnormality (13.70%), acrosome integrity (78.06%), and membrane integrity (80.05%) of sperm remained unaffected. Intratesticular and serum testosterone (T) levels (7.97 ± 0.89 ng/mg protein and 2.47 ± 0.59 ng/mL, respectively), serum luteinizing hormone (LH), growth hormone (GH) levels (1.71 ± 0.24 and 3.62 ± 0.33 ng/mL, respectively) of LTZ groups were elevated, whereas intratesticular and serum estradiol (E2) levels (84.14 ± 8.15 pg/mg protein and 32.33 ± 2.16 pg/mL, respectively) decreased (P < 0.05). No differences were recorded between the sc and im routes of LTZ administration in the measured parameters. To conclude, we have found that LTZ treatment improves growth and reproductive functions of goat bucklings associated with increased serum LH and GH, elevated T and reduced E2 levels in both serum and testis.

Can maintenance intake reduce production costs without compromising the reproductive performance in bucks?

Excessive intake of nutrients can result in decreases in the reproductive efficiency of goat bucks and increase production costs in goat e nterprises. In this study, the aim was to compare the reproductive features of young bucks fed diets for maintenance of growth or were fed ad libitum. Ten bucks were used (n = 5/group), with a completely randomized design. Blood and semen were collected from each animal every 2 weeks for nine collections. Semen was frozen and later analyzed using flow cytometry to compare reactive oxygen species, plasma membrane integrity, acrosome integrity, and membrane lipid peroxidation. Body condition score, sexual behavior, testicular biometry and histomorphometry of the testis, as well as oxidative enzymes and carbonylated proteins, were also evaluated. Animals fed ad libitum had a greater body condition score (3.32 + 0.08 × 2.88 + 0.05), sperm volume (0.68 + 0.04 × 0.52 + 0.03 mL), and testis circumference (25.2 + 0.21 × 24.5 + 0.24 cm) and volume (121 + 5.83 × 107 + 4.38 cm³, left testicle; 116 + 5.26 × 100 + 3.75 cm³, right testicle). Ejaculates of the bucks fed diets to maintain growth rate had a larger number of minor and total sperm morphology defects. There were no differences in testosterone concentrations and sexual behavior. In conclusion, there can be feeding for growth rate maintenance instead of ad libitum feeding, for the reduction in production costs of young bucks without compromising semen quality and reproductive functions.

Influence of season and climatic variables on testicular cytology, semen quality and melatonin concentrations in crossbred bucks reared under subtropical climate

Seasonality in reproduction and effects of climatic variables on testicular cytology and semen quality in bucks reared under subtropical climatic conditions were not well understood. In the present study, using testicular cytology, semen evaluation and melatonin concentrations assessed over a period of 1 year, we report that bucks reared under subtropical climatic conditions did not show seasonality in reproduction. Climatic variables including temperature, relative humidity, temperature-humidity index (THI), sunshine hours and day length were recorded daily during the whole period of experimentation (one complete year). Ejaculates were collected from crossbred (Alpine X Beetal) males (n = 6) biweekly using artificial vagina, and semen quality (volume, mass activity, sperm concentration, motility, viability, membrane integrity and protamine deficiency) was assessed. To understand the seasonal influence at testicular level, using fine needle aspiration biopsy method, testicular cells were aspirated and different types of cells and testicular cytology indices were quantified. Blood was collected biweekly for estimation of melatonin concentrations. Mass activity was higher (P < 0.05) during rainy season while individual sperm motility and sperm concentration were higher (P < 0.05) during rainy and autumn seasons as compared to other seasons. Sperm functional parameters did not show any differences during different seasons. Sertoli cell count, spermatogenic cell count and testicular indices did not differ among the seasons. Melatonin concentrations also did not differ significantly among the four seasons studied. Among the climatic parameters, THI had significant (P < 0.05) influence on sperm quality. The proportion of Sertoli cell in the testicular cytology had a significant and positive relationship with RH, THI and day length. It was concluded that seasonal variations are less evident in terms of spermatogenesis and semen quality in Alpine X Beetal crossbred bucks reared under subtropical climatic conditions.

Correlation of biochemical constituents of seminal plasma with semen quality in Teddy goat (Capra hircus) bucks

This study was planned to determine the relationship between semen quality parameters and the levels of biochemical constituents of seminal plasma of Teddy (Capra hircus) buck semen. For this purpose, semen ejaculates were collected from five mature healthy Teddy bucks. All the experimental bucks were kept under natural environmental conditions. Semen was collected twice in a week for the duration of 6 weeks by Artificial Vagina (AV) in the breeding season (February-April). Two successive ejaculates of single buck were pooled at time of collection, and a total of 60 semen samples were processed for semen analysis. Sperm per cent motility, sperm concentration, dead sperm percentage, morphological abnormal spermatozoa, plasma membrane integrity were correlated with biochemical constituents of seminal plasma. The mean per cent motility (89.18% ± 0.37%), sperm concentration (1.86 ± 0.04 × 10⁹ /ml), dead sperm percentage (8.08% ± 0.29%), morphological abnormal spermatozoa (6.05% ± 0.29%) and plasma membrane integrity (88.22% ± 0.34%) were recorded. The seminal plasma contained Na⁺ (144.12 ± 1.59 mEq/L), K⁺ (27.38 ± 0.49 mEq/L), Cl^- (65.73 ± 0.45 mEq/L), Ca⁺⁺ (9.34 ± 0.22 mg/dl), P (19.32 ± 0.97 mg/dl), aspartate aminotransferase (AST; 26.48 ± 1.30 IU/L), alanine aminotransferase (ALT; 168.47 ± 5.18 IU/L), lactate dehydrogenase (LDH; 215.98 ± 6.06 IU/L), albumin (1.90 ± 0.10 g/dl), globulins (2.08 ± 0.11 g/dl) and total protein (3.98 ± 0.20 g/dl). The collected data were analysed by applying Pearson's correlation coefficients. Dead sperm percentage had negative correlation with sodium (r = -.278, p < .05), albumin (r = -.294, p < .05), globulin (r = -.266, p < .05) and total protein (r = -.295, p < .05). Phosphorus was negatively associated with sperm concentration (r = -.262, p < .05). AST was negatively correlated with plasma membrane integrity (r = -.292, p < .05). It was concluded that most of the semen quality parameters of Teddy bucks were positively correlated with biochemical constituents, but opposite trends were found in case of dead sperm percentage. The seminal biochemical constituents dynamically interact with each other.

Effects of season and artificial photoperiod on semen and seminal plasma characteristics in bucks of two goat breeds maintained in a semen collection center

Aim:

This study quantified the effects of season and photoperiodic treatment on semen and seminal plasma (SP) characteristics in 12 bucks of two Spanish goat breeds (Murciano-Granadina, and Payoya) for the past 1 year.

Materials and Methods:

A total of 6 bucks (three of each breed) were exposed to the natural day length and the other six males (three of each breed) were exposed to alternating conditions of 2 months of long days (16 h light) and 2 months of short days (8 h light). Weekly concentrations of glutamic oxaloacetic transaminase/aspartate aminotransferase (GOT/AST), lactate dehydrogenase (LDH), potassium, testosterone, and protein in SP were measured. Reaction time and scrotal circumference were recorded, and plasma testosterone concentrations were measured before semen collection.

Results:

Sperm volume, LDH, and potassium concentration in SP, and reaction time did not differ significantly between breeds, seasons, and photoperiodic treatment. Sperm concentrations were higher (p<0.001) in spring and summer than they were in autumn and winter. Mean percentage of positive hypo-osmotic swelling test sperm was the highest in summer and under the artificial photoperiod (p<0.01). GOT/AST concentrations differed (p<0.01) between breeds and seasons. Breed, season, and photoperiod had significant (p<0.001) effects on protein and testosterone levels in SP. Plasma testosterone concentrations were highest in summer (p<0.001), and differed significantly (p<0.01) between breeds. Scrotal perimeter differed significantly (p<0.001) between breeds and photoperiod.

Conclusion:

Recognition of those seasonal and breed-specific differences in the performance of bucks should help to improve the management of individual semen samples for use in artificial insemination programs.