Understanding and evaluating bovine testes

Sperm traits and seminal plasma proteome of locally adapted hairy rams subjected to intermittent scrotal insulation

The present study evaluated the effects of heat stress on reproductive parameters of hairy rams. Six animals were subjected to scrotal insulation during four consecutive nights (6 PM - 6 AM). Day (D) 0 was the first day of insulation. Scrotal circumference increased from 30.5 ± 0.3 cm (at pre-insulation) to 31.8 ± 0.4 cm on D4, decreased 3.9 cm on D28, returning to 30.6 ± 0.6 cm on D57. Sperm concentration decreased from 3.7 ± 0.12 ×109 sperm/mL before insulation to 2.6 ± 0.1 ×109 on D23, returning to normal on D57. Sperm motility averaged 75 ± 2.9% before insulation, was undetectable on D23, and became normal on D77. Sperm with normal morphology reached 5.9 ± 2.6% on D35 but recovered (86.8 ± 2.1%) on D91. Sperm DNA integrity decreased from 86.5 ± 4.7% before insulation to 11.1 ± 3.7% on D63, returning to pre-insulation values on D120. Sperm BSP immunostaining was reduced after scrotal insulation. Variations in seminal protein abundances coincided with changes in sperm parameters. Seminal plasma superoxide dismutase, carboxypeptidase Q-precursor and NPC intracellular cholesterol transporter 2 decreased on D18, returning to normal after D28. Albumin, inhibitor of carbonic anhydrase precursor, EGF-like repeat and discoid I-like domain-containing protein 3 and polymeric immunoglobulin receptor increased after insulation. In summary, intermittent scrotal insulation drastically altered ram sperm attributes and seminal proteins, especially those associated with oxidative stress. Knowledge of animal´s response to thermal stress is vital in the scenario of climate changes.

Transcriptomic analysis of the HPG axis-related tissues reveals potential candidate genes and regulatory pathways associated with testicular size in Hu sheep

Testicular size is an excellent proxy for selecting high-fertility rams. The hypothalamus-pituitary-gonadal (HPG) axis plays an important role in regulating reproductive capacity in vertebrates, while key genes and regulatory pathways within the HPG axis associated with testicular size remain largely unknown in sheep. This study comprehensively compared the transcriptomic profiles in the hypothalamus, pituitary and testis of rams after sexual maturity between the large-testis group (LTG, testicular weight = 454.29 ± 54.24 g) and the small-testis group (STG, testicular weight = 77.29 ± 10.76 g). In total, 914, 795 and 10518 differentially expressed genes (DEGs) were identified in the hypothalamus, pituitary and testis between LTG and STG, respectively. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses showed that these DEGs were mainly involved in the biological processes of reproduction, biological regulation, and development process. Notably, the neuroactive ligand-receptor interaction and cAMP signaling pathways, commonly enriched by the DEGs in the hypothalamus and pituitary between two groups, were considered as two key signal pathways regulating testicular development through the HPGs axis. Weighted gene co-expression network analysis (WGCNA) identified two modules that were significantly associated with testicular size, and 97 key genes were selected with high module membership (MM) and gene significance (GS) in these two modules. Finally, a protein-protein interaction (PPI) network was constructed, and ten genes with the highest degree were represented as hub genes, including FOS, NPY, SST, F2, AGT, NTS, OXT, EDN1, VIP and TAC1. Taken together, these results provide new insights into the molecular mechanism underlying the HPG axis regulating testicular size of Hu sheep.

Molecular characterization of SPATA6 and association of its SNPs with testicular size in sheep

The testis is an important organ for maintaining fertility in males, and testis size is positively correlated with ejaculate volume, sperm motility, thus fertility. Spermatogenesis-associated 6 (SPATA6) is an evolutionarily conserved testis-specific gene reported in many species. However, the effect of SPATA6 expression levels on testicular development and the effect of single nucleotide polymorphisms (SNPs) on testis and epididymis phenotype in sheep have not been studied. The purpose of the research was to investigate the expression profile of SPATA6 and its effect on testicular development and to confirm the effect of SNPs on the testis and epididymis phenotype. In this study, we detected a 1245bp coding sequence (CDS) of SPATA6 and encoded 414 amino acids. The expression levels of SPATA6 were significantly higher in the testis than in other tissues and gradually increased with testis development. Moreover, the expression level in the large testis was significantly higher than that in the small testis at six months. A total of 11 SNPs were detected in the coding region of SPATA6 by cDNA-pooling sequencing and improved multiplex ligation detection reaction (iMLDR) methods. Correlation analysis showed that SNP2 (c. 3631C > G) significantly affected left epididymis weight (LEW) and right epididymis weight (REW), and SNP10 (c. 937 A > G) significantly affected REW. And the combined genotype of SNP1 (c. 4245 G > A) and SNP2 significantly affected REW. The current study concluded that SPATA6 plays an important role in testicular development and the SNPs significantly associated with the epididymis phenotype can provide molecular markers for the early selection of high-fertility Hu sheep.

iTRAQ-based proteomic analysis provides novel insight into the postnatal testicular development of Hu sheep

Testicular development is an intricate and coordinated process in which thousands of proteins are involved in the regulation of somatic cells development and spermatogenesis. However, knowledge about the proteomic changes during postnatal testicular development in Hu sheep is still elusive. The study was conducted to characterize the protein profiles at four key stages during postnatal testicular development, including infant (0-month-old, M0), puberty (3-month-old, M3), sexual maturity (6-month-old, M6) and body maturity (12-month-old, M12), and between the large- and small-testis groups at 6 months in Hu sheep. Consequently, 5252 proteins were identified using isobaric tags for relative and absolute quantification (iTRAQ) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods, and 465, 1261, 231 and 1080 differentially abundant proteins (DAPs) were found between M0_vs_M3, M3_vs_M6L, M6L_vs_M12, and M6L_vs_M6S, respectively. GO and KEGG analysis revealed that the majority of DAPs were involved in cellular process, metabolic process and immune system-related pathways. Furthermore, a protein-protein interaction network was constructed using 86 fertility-related DAPs, and five proteins with the highest degree were represented as hub proteins, including CTNNB1, ADAM2, ACR, HSPA2 and GRB2. This study provided new insights into the regulation mechanisms of postnatal testicular development and identified several potential biomarkers for selecting the high-fertility rams. SIGNIFICANCE OF THE STUDY: Testicular development is an intricate developmental process in which thousands of proteins are involved in regulating the somatic cells development and spermatogenesis. However, knowledge about the proteome changes during postnatal testicular development in Hu sheep is still elusive. This study provides comprehensive insights into the dynamic changes in the sheep testis proteome during postnatal testicular development. Additionally, testis size is positively correlated with semen quality and ejaculation volume, also for the merits of easy measurement, high heritability and selection efficiency, is an important indicator to select candidate rams with high fertility. The functional analyses of the acquired candidate proteins may help us gain a better understanding of the molecular regulatory mechanisms of testicular development.

Combined analysis of mRNA-miRNA from testis tissue in Tibetan sheep with different FecB genotypes

Testis size is important for identifying breeding animals with adequate sperm production. The aim of this study was to survey the expression profile of mRNA and miRNA in testis tissue from rams carrying different FecB genotypes, including the wild-type and heterozygous genotypes in Tibetan sheep. Comparative transcriptome profiles for ovine testes were established for wild-type and heterozygote Tibetan sheep by next-generation sequencing. RNA-seq results identified 3,910 (2,034 up- and 1,876 downregulated) differentially expressed (DE) genes and 243 (158 up- and 85 downregulated) DE microRNAs (miRNAs) in wild-type vs heterozygote sheep, respectively. Combined analysis of mRNA-seq and miRNA-seq revealed that 20 miRNAs interacted with 48 true DE target genes in wild-type testes compared to heterozygous genotype testes. These results provide evidence for a functional series of genes operating in Tibetan sheep testis. In addition, quantitative real-time PCR analysis showed that the expression trends of randomly selected DE genes in testis tissues from different genotypes were consistent with high-throughput sequencing results.

Review: Role of early life nutrition in regulating sexual development in bulls

The availability of high-quality semen from genetically elite bulls is essential to support continued genetic gain and the sustainability of cattle production worldwide. While reducing the age at which usable semen is available also reduces the generation interval, it is dependent on timely onset of puberty in young bulls. There is now good evidence that hastened sexual development in bulls is achieved through enhancing nutrition in early life. This review will cover the physiological and molecular-based response to prevailing diet in key organs that orchestrate the ontogeny of sexual development in the bull calf. Given the central importance of the interaction between metabolic status and neuronal function to the progression of sexual development, we will discuss how communication between metabolic organs, reproductive organs and the brain are mediated via molecular and physiological processes. The availability of high-throughput nucleic acid and protein sequencing technologies and innovative data analytics have allowed us to improve our understanding of molecular regulation of puberty and sexual development. Analysing data from a number of organs, simultaneously, allows for a better understanding of the underlying biology and biochemical interactions that are influencing sexual development. Specifically, we can determine how early life nutritional interventions augment changes in potential key molecules regulating sexual development. Ultimately, a greater understanding of the inherent regulation of postnatal sexual development in the bull calf and how strategically targeted nutritional management can advance the ontogeny of this process, will facilitate the timely availability of high-quality semen from genetically elite animals, thus supporting more economically and environmentally sustainable beef and dairy production systems.

Identification of Y-SNPs within ovine MSY region and their association with testicular size

The screening of genomic variations within the male-specific region of the mammalian Y chromosome (MSY) is one of the most effective ways to investigate paternal evolutionary history and identify molecular markers related to male fertility. The current study was to identify single nucleotide polymorphisms (SNPs) within single-copy genes of the ovine MSY, and confirm whether they are associated with testicular size. A total of 21 Y-specific gene fragments were successfully amplified to screen Y-SNPs in 956 rams across nine sheep breeds. Three Y-SNPs, including SRY16: g.88 A > G in South African Mutton Merino sheep, ZFY16: g.146 C > T in Suffolk and South African Mutton Merino sheep, and EIF2S3Y2: g.77 C > G in Hu and Tan sheep, were identified using DNA-pooled sequencing and PCR restriction fragment length polymorphism (PCR-RFLP) methods. The investigation of the global distribution for three Y-SNPs showed that the C allele of ZFY16: g.146 C > T co-segregated with haplogroup y-HC, and the C/G allele of EIF2S3Y2: g.77 C > G co-segregated with haplogroup y-HA/y-HB1 in Hu sheep according to data mining from a previous study. In addition, association analysis revealed that ZFY16: g.146 C > T had a significant effect on yearling scrotal circumference in Suffolk sheep, and EIF2S3Y2: g.77 C > G was significantly associated with testicular and epididymis weight in Hu sheep (P ≤ 0.05). The current study concluded that Y-SNPs were associated with testicular size in specific sheep, which provides valuable candidate makers for selecting elite rams at an early age.

Environmental Factors Affecting the Reproductive Efficiency of Italian Simmental Young Bulls

The objectives of the study aimed to evaluate the effect of weather conditions and scrotal circumference (SC) on standard semen characteristics of Italian Simmental young bulls (n = 577), all raised in the same performance station and sampled by the artificial vagina (AV) method. Considering the increasing SC, the results showed a significant increase in quantitative semen parameters (p < 0.05 and p < 0.0001, for sperm concentration and total number of spermatozoa, respectively); for every extra centimeter of SC, 17.5 × 106 spermatozoa/mL and 0.102 × 109 of total spermatozoa were produced. The age of the animal at semen collection (395 and 465 days) had similar positive effects. The effect of the average temperature humidity index (THI limits ≤ 40 and ≥70) in the previous 60, 30, and 10 days before the semen collection was also considered. Sixty days before the semen collection, the increasing THI increased both primary (p < 0.0001) and secondary (p < 0.0001) abnormalities while the percentage of morphologically normal spermatozoa decreased (p < 0.0001). Thirty and ten days before collection, the same effect on morphological traits was maintained, but total and progressive motility was also influenced (p < 0.01) with an unexpected increasing pattern. Thus, environmental conditions can influence semen quality during the entire spermatogenesis and results can guide future research on this breed.

Identification of Key Genes Related to Postnatal Testicular Development Based on Transcriptomic Data of Testis in Hu Sheep

The selection of testis size can improve the reproductive capacity of livestock used for artificial insemination and has been considered as an important strategy for accelerating the breeding process. Although much work has been done to investigate the mechanisms of testis development in various species, there is little information available in regard to the differences in transcriptomic profiling of sheep testes at different developmental stages. In this work, we aimed to identify differentially expressed genes (DEGs) by RNA-Seq in sheep during different growth stages, including 0 month old (infant, M0), 3 months old (puberty, M3), 6 months old (sexual maturity, M6) and 12 months old (body maturity, M12). A total of 4,606 (2,381 up and 2,225 down), 7,500 (4,368 up and 3,132 down), 15 (8 up and seven down) DEGs were identified in M3_vs_M0, M6_vs_M3, and M12_vs_M6 comparison, respectively. Of which, a number of genes were continuously up-regulated and down-regulated with testicular development, including ODF3, ZPBP1, PKDREJ, MYBL1, PDGFA, IGF1, LH, INSL3, VIM, AMH, INHBA, COL1A1, COL1A2, and INHA. GO analysis illustrated that DEGs were mainly involved in testis development and spermatogenesis. KEGG analysis identified several important pathways and verified several reproduction-associated DEGs such as COL1A1, COL1A2, PDGFA, and IGF1. In addition, two gene modules highly associated with testis development and core genes with testis size were identified using weighted gene co-expression network analysis (WGCNA), including hub genes positively associated with testis size such as RANBP9, DNAH17, SPATA4, CIB4 and SPEM1, and those negatively associated with testis size such as CD81, CSK, PDGFA, VIM, and INHBA. This study comprehensively identified key genes related to sheep testicular development, which may provide potential insights for understanding male fertility and better guide in animal breeding.

How the environment affects early embryonic development

In the field of animal reproduction, the environment associated with gametes and embryos refers to the parents' condition as well as conditions surrounding gametes and embryos in vivo or in vitro . This environment is now known to influence not only the functionality of the early embryo but potentially the future phenotype of the offspring. Using transcriptomic and epigenetic molecular analysis, and the bovine model, recent research has shown that both the female and the male metabolic status, for example age, can affect gene expression and gene programming in the embryo. Evidence demonstrates that milking cows, which are losing weight at the time of conception, generates compromised embryos and offspring with a unique metabolic signature. A similar phenomenon has been associated with different culture conditions and the IVF procedure. The general common consequence of these situations is an embryo behaving on 'economy' mode where translation, cell division and ATP production is reduced, potentially to adapt to the perceived future environment. Few epidemiological studies have been done in bovines to assess if these changes result in a different phenotype and more studies are required to associate specific molecular changes in embryos with visible consequences later in life.

Effects of Extender Type, Storage Time, and Temperature on Bull Semen Parameters

Seminal parameters can be evaluated in situ, or samples can be delivered to a diagnostic centre. How storage conditions affect ejaculates up to evaluation is unclear. We assessed, in 25 commercial bulls electroejaculated in the field, the impact of time until evaluation (0-2 h, 4-6 h, and 24 h post-ejaculation), holding temperature (5 °C vs. room temperature), and extender (AndroMed^®, BIOXcell^® or INRA96^®) on semen quality. Acrosome integrity, sperm viability and morphology, CASA-total and progressive motility, pH, and colony-forming units were assessed. Semen quality was preserved for up to 4-6 h post-ejaculation, except for INRA96^® at 5 °C. Regardless of extender or temperature, motility decreased from 4 to 6 h up to 24 h, with the best values obtained with BIOXcell^® at 5 °C. pH differed from 4 to 6 h up to 24 h, acidifying when stored at room temperature. Microbiological load was stable over time with AndroMed^® and BIOXcell^®, and increased at room temperature with INRA96^®. Our results suggest that AndroMed^® and BIOXcell^® can preserve semen quality for up to 6 h, either at 5 °C or room temperature, while INRA96^® only at room temperature. These results help to fix adequate protocols for short-term storage and shipment of bovine semen collected under field conditions.

Scrotal thermoregulation and sequential sperm abnormalities in buffalo bulls (Bubalus bubalis) under short-term heat stress

Heat stress reduces the reproductive capacity of bulls raised in tropical climate. However, the reestablishment of scrotal thermoregulation and the dynamics of sperm defects emergence after stress are not completely known in buffaloes. Thus, the study aimed to evaluate the effect of short-term heat stress over scrotal thermoregulation and sperm attributes, relating them to spermatogenesis stages. Five buffalo bulls went through scrotal insulation during 48 h (from day 0 to day 2). Semen samples were collected every 7 days (from day -7 to day 49) and analyzed about the progressive motility, viability, and sperm morphology. Heat stress significantly destabilized scrotal thermoregulation (P < 0.001). Scrotal temperature was from 4.2 to 6.3 °C lower than the core body temperature, except on insulation days (P < 0.001), and returned to the basal condition five days after the removal of the stressing stimulus. More significant deleterious effects were observed in sperm morphology than in cell concentration, motility, and viability. The chronology of morphologic defects expression demonstrated tail defects (days 7-14), cytoplasmic droplets (days 14-28), and head defects (day 28), returning to pre-insulation condition 35 days after the thermal challenge. Thus, hyperthermia harmed more intensely spermatozoa in epididymal transit, elongated spermatids, and secondary spermatocytes. It is concluded that water buffalo bulls present a peculiar manifestation of sperm morphology after short-term stress, indicating an important difference related to the bovine species. Therefore, during the andrological evaluation of buffalo bulls, it is necessary to avoid the allometric extrapolation between these species.

Shade availability on pasture does not affect semen characteristics of Brahman bulls (Bos taurus indicus)

Testicular degeneration by heat is the leading cause of infertility in bulls. Beef cattle are generally farmed under hot and humid conditions, and consequently, the thermotolerance of each breed must be considered in their natural environment. This study aimed to evaluate the reproductive characteristics of Brahman bulls maintained in the grazing system, with or without shadow availability. Ten Brahman bulls aging between 24 and 30 months were allocated in two different paddocks, with or without shadow availability. The heat tolerance test was performed on three non-consecutive typical summer days. The semen samples were collected at four times points in a 14 days interval. The climate conditions were monitored throughout the experiment; and clinical evaluation, testicular consistence and scrotal circumference were measured before every semen collection. In addition, semen was evaluated regarding volume, aspect, turbulence, motility, straight movement, sperm concentration, and morphological exam. The studied Brahman bulls showed a high thermolysis capacity, high heat tolerance, and no differences in semen quality were observed between groups.

Reproductive parameters of Bos taurus and Bos indicus bulls during different seasons in tropical conditions: focus on an alternative approach to testicular assessments using ultrasonography

The aim of the present study was to evaluate the reproductive status of Bos taurus and Bos indicus bulls during different seasons when bulls were in a tropical environment focusing on systematic assessment of the testes using B-mode ultrasonography and ImageJ software to evaluate the testicular parenchymal tissues. The experimental design is a 2 × 2 factorial arrangement, with breed (Bos Taurus - Simmental; Bos indicus - Nellore) and season (summer; winter) as factors. Testicular ultrasonic evaluation and conventional semen analysis were performed. The Simmental bulls had more major sperm defects than Nellore bulls in the summer (P = 0.0001). Additionally, Simmental bulls had a greater percentage of major sperm defects during the summer than winter months P = 0.045). Furthermore, Nellore bulls had a greater testicular parenchyma echogenicity, with a greater grayscale, (caudal parenchyma, P = 0.0155; cranial parenchyma, P = 0.001) and mediastinum grayscale than Simmental bulls (Nellore = 52.32 ± 03.60; Simmental = 35.72 ± 03.67; P = 0.003). Simmental bulls also had a greater testicular lesion area (P = 0.0147). Results indicated there was susceptibility to heat stress when Simmental bulls were maintained in tropical regions. The results of the present study indicate there is an association between results when there was use of conventional andrological evaluation procedures and results from ultrasonic analysis using ImageJ software that allows for earlier identification of tissue aberrations that could lead to impaired semen quality and fertility.

Histological Comparison of Testicular Needle Biopsy and En Bloc Samples in Abattoir Calves

the aim of this study was to test whether a single testicular needle biopsy could provide histological results comparable to en bloc resection histology and whether one biopsy was sufficient to reflect the histology of an entire pair of testicles. Two methods of sample collection were tested on 32 bull calves aged five to eight months to compare histological parameters of needle biopsy with those of en bloc resection samples. One testicular needle biopsy of the right and three en bloc samples of both testicles were collected and compared for the number of tubular cross sections, tubules with elongated spermatids (ES), outer/inner diameter of tubules, thickness of tubular wall, and number of Sertoli cells (SC). Additionally, animal data were considered. No significant differences were found between the left and right testis or among the individual locations of en bloc samples. However, histologically significant differences (Bonferroni-adjusted significance level: p < 0.05/6 = 0.0083) were found between the needle biopsy and en bloc resection regarding the tubular cross sections per visual field (p < 0.05), the outer (p = 0.01) and inner diameter and the thickness of the tubular wall (both p < 0.01). In the SOX9 immunohistochemical staining, no significant differences (p > 0.05) could be observed for SC numbers between needle biopsy and en bloc samples. In conclusion, results of testicular needle biopsy do not have the same validity as the en bloc resection histology. Furthermore, one biopsy is insufficient to reflect the histology of the entire testicular pair.

Expression of DAZL Gene in Selected Tissues and Association of Its Polymorphisms with Testicular Size in Hu Sheep

Simple Summary

The deleted in azoospermia-like (DAZL) is an RNA binding protein coding gene in autosomal, playing important roles in testicular development and gametogenesis. In this paper, we found that DAZL is extremely highly expressed in testis compared with other organs and reaches to a peak at sex maturity (6-month old) in testis. Two single nucleotide polymorphisms (SNPs) within DAZL were found to have significant effect on the variation coefficient between left and right epididymis weight.

Abstract

The deleted in azoospermia-like (DAZL) gene encoding an RNA binding protein is pivotal in gametogenesis in lots of species and also acts as a pre-meiosis marker. The current study was conducted to detect expression profiles and single nucleotide polymorphisms (SNPs) of DAZL in sheep using qPCR, DNA-pooled sequencing, improved multiplex ligase detection reaction (iMLDR^®) and restriction fragment length polymorphism (RFLP) methods. The results confirmed that ovine DAZL showed the highest expression level at six-months of age across five developmental stage. At six-month stage, DAZL expressed primarily in testis across seven tissues analyzed. The abundance of DAZL in the large-testis group is higher than that in the small-testis group although it is not significant. In addition, six SNPs (SNP1-SNP6) were identified in DAZL. Of those, SNP1 (p < 0.05) and SNP6 (p < 0.01) were significantly correlated with the variation coefficient between left and right epididymis weight (VCTW). The current study implies DAZL may play important roles in testicular development and its SNPs are associated with testicular parameters, which supply important indicators for ram selection at early stage.

Evaluation of ovarian volume by transrectal ultrasonography in cattle; affect of the day of the estrous cycle and validation of a method of subtracting of corpora lutea and follicle volume

This research was conducted to evaluate a method for determining ovarian volume using ultrasonography; specifically, how the day of the estrous cycle affected ovarian volume, and the application of a formula for adjusted ovarian volume (ADJ VOL) and its relationship to actual ovarian volume. Cows (n = 22) were estrous synchronized and subjected to serial transrectal ultrasonographic evaluations, performed every 48 h from the day prior to ovulation until day 9 of the subsequent estrous cycle. Measurements obtained from recorded ultrasonographic images were used to determine actual ovarian volume cm³ = [0.523 X (D1 X D2 X D3)] and adjusted ovarian volume (ADJ VOL) cm³ = [0.523 X (D1 X D2 X D3)]- 43 (πrCL²) - 43 (πrF²) on days 1, 3, 5, 7, 9 of the estrous cycle. A third objective was to evaluate the concordance correlation coefficient (ρc) between post-mortem ovarian measurements and the water displacement test. Ovarian volume increased with each day of the estrous cycle from Day 1 to Day 7. Day of the estrous cycle affected ovarian volume (P <  0.001). When applying the formula for ADJ VOL, there was not an effect of day of the estrous cycle (P  = 0.509). Ovarian volume, results ex-vivo, were very consistent with the displacement volume results (ρ_c = 0.942). If large ovarian structures are present, and the day of the estrous cycle is unknown, then the formula for ADJ VOL can be used to estimate ovarian volume on Day 1 of the estrous cycle.

Association of α/β-Hydrolase D16B with Bovine Conception Rate and Sperm Plasma Membrane Lipid Composition

We have identified a Holstein sire named Tarantino who had been approved for artificial insemination that is based on normal semen characteristics (i.e., morphology, thermoresistance, motility, sperm concentration), but had no progeny after 412 first inseminations, resulting in a non-return rate (NRdev) of -29. Using whole genome association analysis and next generation sequencing, an associated nonsense variant in the α/β-hydrolase domain-containing 16B gene (ABHD16B) on bovine chromosome 13 was identified. The frequency of the mutant allele in the German Holstein population was determined to be 0.0018 in 222,645 investigated cattle specimens. The mutant allele was traced back to Whirlhill Kingpin (bornFeb. 13th, 1959) as potential founder. The expression of ABHD16B was detected by Western blotting and immunohistochemistry in testis and epididymis of control bulls. A lipidome comparison of the plasma membrane of fresh semen from carriers and controls showed significant differences in the concentration of phosphatidylcholine (PC), diacylglycerol (DAG), ceramide (Cer), sphingomyelin (SM), and phosphatidylcholine (-ether) (PC O-), indicating that ABHD16B plays a role in lipid biosynthesis. The altered lipid contents may explain the reduced fertilization ability of mutated sperms.

Ultrasonographic characteristics of the testes, epididymis and accessory sex glands and arterial spectral indices in peri- and post-pubertal Nelore and Caracu bulls

Ultrasonography can provide information about the integrity of organs; however, rarely is applied to the reproductive organ evaluation of bulls. The objective of the present study was to characterize and compare values for variables and ultrasonographic characteristics of the testes, epididymis and accessory sex glands, as well as spectral Doppler indices of the testicular and internal iliac arteries, between peri- and post-pubertal Nelore and Caracu bulls. Nelore (n = 203) and Caracu (n = 79) bulls were assigned by age class: peri-pubertal (12-15 months) and post-pubertal (> 22 months). Data were analyzed using SAS's PROC MIXED procedure (P < 0.05). The biometric variables of the testes and cauda epididymis differed between peri- and post-pubertal Nelore and Caracu bulls. There was a difference between breeds for the vesicular glands, ampulla of vas deferens, disseminate portion of the prostate, and craniocaudal dimension of the bulbourethral glands. Echogenicity of the testicular parenchyma differed between breeds and age classes. The pulsatility and resistive indices of the testicular arteries differed between Nelore and Caracu bulls. The biometric and ultrasonographic characteristics of the testes, epididymis and accessory sex glands, as well as of the arterial indices in bulls are affected by genetic group and age class, and when assessed there is useful information regarding the progression of sexual maturation.

Reproductive characteristics of bulls from two breed compositions and their correlations with infrared thermography

The objective was to evaluate reproductive characteristics of crossbred Girolando (Gyr x Holstein) bulls from two breed compositions and correlate these results with infrared thermography data. Evaluations were performed considering sperm motility, vigor and morphology; scrotal circumference; body morphology and temperament. Infrared thermography was performed to determine surface temperatures of ocular and scrotal areas. Thermoregulation capacity was assessed by differences between air and rectal temperatures, air and maximum temperatures in ocular and scrotal areas, and dorsal and ventral lines of the scrotum. Data analysis was performed using a linear mixed model (breed composition as fixed effect and year of evaluation as random effect). Spearman correlation coefficient was used to associate thermography and reproductive data. Girolando 3/4 Holstein bulls had higher (P ≤ 0.001) scrotal circumference and higher average body morphology and temperament, whereas 5/8 Holstein bulls had a higher (P < 0.001) percentage of major-type and total sperm defects. Girolando 3/4 Holstein bulls had scrotal temperatures 0.8 °C higher (P < 0.001) and 5/8 Holstein bulls had 9.8% and 10.6% higher differences on "rectal - scrotal area" and "ocular area - scrotal area" temperatures, respectively. Ocular area temperatures had negative correlations (P ≤ 0.1) with sperm motility and vigor, and positive correlations (P < 0.001) with minor-type and total sperm defects. Ventral line scrotal temperatures had positive correlations (P < 0.001) with minor-type and total sperm defects. Girolando 3/4 Holstein bulls were found to be superior to 5/8 Holstein bulls for reproductive characteristics. Under non-stressing climatic conditions, semen characteristics of Girolando bulls were more influenced by breed composition than by the capacity for scrotal thermoregulation. Correlations between semen quality and scrotal temperatures can aid in the identification of bulls for breeding, particularly when a large number of animals are in the tests.

Scrotal infrared thermography and testicular biometry: Indicator of semen quality in Murrah buffalo bulls

This aim of this study was to assess the relationship, if any, of scrotal surface temperature gradient (SSTG), scrotal circumference (SC) and testicular covering thickness (TCT) with semen quality in Murrah buffalo breeding bulls. For this, buffalo breeding bulls (n = 130) were selected from four different semen centres. The ejaculates of each bull were evaluated for ejaculate volume (EV), mass motility (MM); concentration (SPC), motility (SM), viability and abnormalities (SA). The SSTG, SC and TCT of individual bulls were quantified using digital infrared thermography, measuring tape and ultrasonography, respectively. The bulls were divided into three groups on the basis of SSTG (≤ 4 °C, 4.1 to 6.4 °C and ≥ 6.5 °C), and SC (<31, 31 to 35 and> 35 cm) and into two groups on the basis of TCT (5 to 7.2 and 7.4 to 10.4 mm). Results indicated the bulls with a larger temperature gradient and larger SC produced greater quality semen than those with a lesser temperature gradient. The MM (P < 0.01) and SPC (P < 0.05) varied among the groups along with SSTG. Among the SC groups the EV, MM, SPC and SM (P < 0.01), and viability (P < 0.05) varied as did the SC. The bulls with a lesser TCT had a lesser SA (P < 0.05) as compared to the group with the greater TCT. Buffalo bulls having a greater SSTG, SC and lesser TCT produced semen of greater quality and these variables may be used as criteria for breeding soundness evaluation.

Sexual maturity and fertility-related measures in young Nellore bulls receiving long-term dietary supplementation with rumen-protected polyunsaturated fatty acids

The objective of this study was to evaluate the effects of long-term supplementation with rumen-protected fatty acids (FA) on growth and reproductive parameters of young Nellore bulls in a grazing regime. Forty-eight young bulls were distributed into two groups: FA (supplemented with rumen-protected polyunsaturated FA); and control (control fat-free supplement). The animals were supplemented from 14.3 to 24.6 months of age and growth and reproductive parameters were evaluated at 28-day intervals. The semen was cryopreserved in the last collection and fresh and post-thaw semen samples were evaluated. Feeding FA did not affect (P > 0.05) growth, reproductive parameters (scrotal circumference, sperm concentration per mL of ejaculate, percentage of sperm defects, sperm quality and fertility in vitro), or testicular ultrasonographic characteristics. However, thawed semen from bulls fed FA exhibited better quality (P < 0.05) than control semen for the following parameters evaluated by computer-assisted sperm analysis: average path velocity [μm/s: 90.48 vs. 79.66 post-thaw and 74.81 vs. 72.80 post-rapid thermoresistance test (TRT)], straight-line velocity (μm/s: 72.37 vs. 65.20 post-thaw and 64.96 vs. 63.25 post-TRT), and curvilinear velocity (μm/s: 148.44 vs. 131.31 post-thaw and 115.68 vs. 113.35 post-TRT). In addition, feeding FA increased peripheral concentrations of testosterone, leptin, total cholesterol and high-density lipoprotein. In conclusion, the increase in testosterone concentrations in bulls fed FA was not related to variations in growth parameters and sexual maturity. In addition, post-thawing sperm velocities were enhanced by diet, however, such increases were not related to better in vitro embryo production rates.

Scrotal circumference, bodyweight and semen characteristics in growing dairy-breed natural-service bulls in Tasmania, Australia

AIMS

To provide herd managers with a set of decision rules allowing them to predict the likelihood that a juvenile bull is ready for Bull Breeding Soundness Evaluation (BBSE), or breeding, if bodyweight and scrotal circumference are known.

METHODS

This was a longitudinal study following two groups of young pasture-fed Holstein and Jersey bulls from northwest Tasmania, Australia. Individual scrotal circumference, bodyweight and semen characteristics were recorded at 6-8 weekly intervals, from 6-18 months of age. Classification and regression tree analyses were used to predict the probability that a bull had ≥70% normal sperm morphology based on scrotal circumference and bodyweight measurements.

RESULTS

Overall 1,661 scrotal circumference and bodyweight measurements were obtained, and 518 semen samples from 356 bulls were assessed for sperm morphology, from 16 examination sessions that took place between 29 May 2015 and 17 August 2016. Classification and regression tree analyses generated a decision tree for Holstein bulls with four node endpoints, and for Jersey bulls with three node endpoints. Diagnostic test performance showed that for Holstein bulls, using the node endpoints of scrotal circumference ≥27 cm and bodyweight ≥349 kg, 98% had ≥70% normal sperm (positive likelihood ratio 10.4; 95% CI = 2.7-41), and using the node endpoints of scrotal circumference ≥27 cm and bodyweight between 282-349 kg, 89% had ≥70% normal sperm (positive likelihood ratio 1.6; 95% CI = 0.9-2.6). For Jersey bulls, using the node endpoints of bodyweight ≥259 kg and scrotal circumference ≥29 cm, 88% had ≥70% normal sperm (positive likelihood ratio 3.4; 95% CI = 1.6-7.0).

CONCLUSIONS

This study provides a set of relatively simple decision rules based on bodyweight and scrotal circumference measurements that allows herd managers to assess the likelihood that juvenile bulls are ready for BBSE or breeding.

ABBREVIATIONS

BBSE: Bull breeding soundness evaluation; BRT: Boosted regression tree.

Impacts of residual feed intake and pre-natal diet on reproductive potential of bulls

Our objective was to determine effects of genetic potential for residual feed intake (RFI) and pre-natal diet on post-natal growth and reproductive development of bulls. Twenty-five bull calves with a divergent potential for RFI were produced by mating purebred Angus heifers (60) categorised as high or low RFI and inseminated with semen from high or low RFI bulls. From 30 to 150 days of gestation, half the heifers (balanced for RFI across treatments) in each RFI category were fed to gain 0.7 or 0.5 kg/day (~100% and 75% of recommended feed intake; designated normal- and low-diet, respectively). Birthweights of bull calves (n = 25) did not differ significantly among treatment groups (P ≥ 0.1). However, there was a tendency (P &lt; 0.1) for a maternal diet*time interaction for bull weights, with bulls from low pre-natal diet fed heifers growing faster between 10 and 16 months of age than bulls from normal pre-natal diet fed heifers. Furthermore, high-RFI bulls had a larger scrotal circumference (P &lt; 0.01) and attained puberty (P &lt; 0.05) earlier than low-RFI bulls. Other testes measures, including paired testes volume, epididymal sperm reserves, daily sperm production and total sperm production, were not significantly different among treatment groups (P ≥ 0.1). High RFI bulls tended (P &lt; 0.1) to have better average sperm motility than low RFI bulls. However, sperm morphology, viability and chromatin damage were not different (P ≥ 0.1). In summary, young beef bulls with low RFI had smaller testis, delayed onset of puberty (~1.7 months) and tended to exhibit lower progressive motility compared with high RFI bulls. Pre-natal diet had no direct influence on male reproductive development, nor did it interact with RFI of bulls.

Impotentia generandi in male dromedary camels: FSH, LH and testosterone profiles and their association with clinical findings and semen analysis data

Impotentia generandi (IG) is a major problem in male dromedary camels. The objective of this research was to characterize the FSH, LH and testosterone profiles and their association with clinical findings and semen characteristics in IG-male dromedaries. Semen was collected by electroejaculation from camels with IG (n = 17) and from a fertile group (FERT, n = 5) and was evaluated for motility, viability, abnormality and concentration. According to their sperm counts, the IG-camels were categorized into three groups: those with normal sperm concentration (IG-NC, n = 8), those with oligospermia (IG-OLIGO, n = 5) and those with azoospermia (IG-AZOO, n = 4). Jugular blood was collected from all camels for analysis of FSH, LH and testosterone (T) concentrations. Results showed that the FSH, LH and T levels were higher in the IG-OLIGO and IG-AZOO groups than in the FERT and IG-NC groups (P < 0.05). The IG-camels with small testes showed lower sperm counts (P < 0.01) and greater FSH and T levels (P < 0.05) than the IG-camels with normal-sized testes. Inverse relationships were observed between the sperm counts and both the FSH and the LH levels (P < 0.05). In conclusion, the IG dromedary camels with oligo- and azoospermia were characterized by high serum levels of FSH, LH and T, indicating a condition of spermatogenic failure. In addition, inverse correlations were observed between these hormones and testicular size and sperm count.

Relationships of plasma insulin-like peptide 3, testosterone, inhibin, and insulin-like growth factor-I concentrations with scrotal circumference and testicular weight in Japanese Black beef bull calves

This study was conducted to clarify the relationships of plasma concentrations of insulin-like peptide 3 (INSL3), testosterone, inhibin, and insulin-like growth factor-I (IGF-I) with scrotal circumference and testicular weight in Japanese Black beef bull calves (n = 20), from birth to pre-puberty. Monthly blood sampling (0 to 7 months) and scrotal circumference measurements (0 to 7 months) were performed. Testicular weight was recorded immediately after castration at 7 months. Plasma INSL3, testosterone, inhibin, and IGF-I concentrations were measured either by enzyme immunoassay or time-resolved fluorescence immunoassay. The correlation coefficients of these hormonal concentrations with scrotal circumference were significant (P < 0.0001) and it was higher for INSL3 (r = 0.647) than for testosterone (r = 0.597), IGF-I (r = 0.400), and inhibin (r = –0.453). Calves with heavier testes (> 60 g) at castration (7 months) had higher (P < 0.05) plasma INSL3 (from 3 to 7 months) and inhibin (from 1 to 4 months) concentrations than those with lighter testes (< 60 g). The calves with heavier testes at castration had larger (P < 0.05) scrotal circumference than those with lighter testes from 3 to 7 months. In conclusion, blood INSL3 concentrations may be the best functional indicator among the hormones analyzed for determining total testicular volume during pre-puberty in bull calves. In addition, inhibin and INSL3 concentrations in early calfhood may be functional predictors for testicular weight at pre-puberty.

High systemic and testicular thermolytic efficiency during heat tolerance test reflects better semen quality in rams of tropical breeds

This study aimed to assess the capacity of Morada Nova (MN) and Santa Inês (SIN) rams to maintain body and testicular homeothermy under thermal challenge. For 5 days in the summer, 16 males (SIN = 7 and MN = 9) underwent a heat tolerance test, i.e., period 1-animals maintained in the shade (11 to 12 h); period 2-animals exposed to sunlight (12 to 13 h); and period 3-animals returned to the shade (13 to 14 h). The respiratory rate, heart rate, rectal temperature, and infrared surface temperatures (IRT) of the trunk, back, eyeball, and testicles were assessed in each period. The index of capacity of tolerance to insolation (ICTI), which indicates the animals' level of adaptability, was calculated for each animal. Semen quality and testicular parenchyma integrity were assessed before and after the thermal challenge. Statistical analyses were performed at 5% significance. In period 1, the variables had baseline values for both genotypes. In period 2, the variables involved in thermolysis significantly increased (P < 0.05), which matches a thermal discomfort situation. In period 3, the variables returned to baseline values and some values were lower than those in period 1. Semen quality and testicular parenchyma integrity suffered no negative effects with the thermal challenge. IRT ocular and IRT testicular were positively correlated (P < 0.05). It is concluded that MN and SIN rams had efficient thermolytic mechanisms that favor preserving gonadal functionality. The animals were considered resilient to a thermal challenge. In addition, infrared thermography was an efficient tool to verify body and testicular thermoregulation.

Diagnosis of lumbosacral diskospondylosis in a bucking bull assisted by high-definition thermal and nuclear scintigraphic imaging

CASE DESCRIPTION An 8-year-old Brahman-cross bull was evaluated for left hind limb lameness of 2 months' duration. The lameness was first noticed during a rodeo bucking performance, immediately after the bull appeared to land inappropriately on the affected limb. CLINICAL FINDINGS Physical examination findings revealed left hind limb lameness, ataxia, and left-sided epaxial muscle atrophy. Palpation per rectum along the lumbar portion of the vertebral column revealed evidence of exostosis of the ventral aspect. High-definition infrared thermal imaging revealed a pattern of reduced skin temperature in the area of the left lumbar and gluteal regions suggestive of a disruption in the sympathetic control of peripheral blood flow. Nuclear scintigraphy revealed a focal area of increased radioisotope uptake on the left ventrolateral aspect of the L2-3 intervertebral joint. A presumptive diagnosis of ventrolateral vertebral spondylosis resulting in spinal nerve impingement was made. TREATMENT AND OUTCOME 200 mg of methylprednisolone was epidurally injected at the site of the lesion, and treatment with polysulfated glycosaminoglycans was initiated (500 mg, IM, every 4 days for 7 treatments, then monthly thereafter). The lameness and ataxia observed in the left hind limb resolved within 1 week after treatment began. Subsequently, the bull was discharged from the hospital and was used successfully for semen collection and live-cover breeding. CLINICAL RELEVANCE Use of thermography for the bull of this report provided additional insight into neurovascular physiologic function that classical imaging modalities are unable to provide and, when combined with nuclear scintigraphy, aided in identifying the most critical lesion in a complex clinical case.

Changes of plasma concentrations of insulin-like peptide 3 and testosterone, and their association with scrotal circumference during pubertal development in male goats

Insulin-like peptide 3 (INSL3) has been used as a testis-specific biomarker for puberty in several species, but the secretory profile of INSL3 during pubertal development in small ruminants is unknown. Here we sought to determine the age-related changes in the plasma concentrations of INSL3 and testosterone and their association with scrotal circumference during pubertal development in five male Shiba goats. Blood samples and scrotal circumference measurement were taken every 2 weeks from week 10 to week 52 of each goat's lifespan. Based on the changes in scrotal circumference, data were grouped into early pubertal (10-22 weeks), late pubertal (22-34 weeks) and post-pubertal (34-52 weeks) categories. The plasma concentrations of testosterone and luteinizing hormone (LH) were measured by enzyme-immunoassays (EIAs), and we used a time-resolved fluorescence immunoassay (TRFIA) to measure plasma INSL3. The biweekly sampling showed that the plasma INSL3 secretions maintained a moderate increase during and after puberty, whereas the plasma testosterone secretions fluctuated over the same period. The comparison of the three age categories revealed a significant increase (p < 0.01) in the mean plasma INSL3 concentrations during the late and post-pubertal periods compared to the early pubertal period. There was no difference in the mean plasma testosterone concentrations between the early and late pubertal periods, but a significant increase (p < 0.01) was observed during the post-pubertal period compared to early and late pubertal periods. The mean plasma LH concentrations increased significantly (p < 0.05) from the early pubertal to late pubertal and from the late pubertal to post-pubertal periods. A significant increase (p < 0.05) in the mean scrotal circumference from the early pubertal to late pubertal and from the late pubertal to post-pubertal periods was observed. The R² value of the best regression curves between scrotal circumference and INSL3 (0.513; p < 0.001) was higher than that between scrotal circumference and testosterone (0.162; p < 0.01) from 10 to 52 weeks of age. In conclusion, in male goats, plasma concentrations of INSL3 increased continuously during and after puberty, whereas testosterone secretions were fluctuated. The scrotal circumference was more highly correlated with the INSL3 concentrations than with testosterone, implying that INSL3 is superior as a biomarker of testicular total Leydig cell volume.

Assessment of surface temperatures of buffalo bulls (Bubalus bubalis) raised under tropical conditions using infrared thermography

This paper aimed to evaluate the surface temperatures of buffalo bulls using infrared thermography, considering four distinct anatomical parts over time, and to correlate surface temperatures and thermal comfort indexes. The humid tropical climate (Köppen's Afi) was predominant in the research station where the experiment was performed and the trial lasted from April to August. Ten bulls (n=10) were evaluated every 25 days (morning: 6:00-9:00; afternoon: 12:00-15:00) and the parameters assessed were respiratory rate (RR), rectal temperature (RT), and the thermograms of surface temperature for orbital area (ORB), right flank (RF), left flank (LF) and scrotum (SCR). Climatological data was continuously monitored and the Temperature and Humidity Index (THI) and the Index of Comfort of Benezra (ICB) were calculated. The average values of THI were ≥78, and significant differences between shifts were observed (P<0.05). The ICB ranged from 1.96 to 2.25 and significant differences were observed for shifts and throughout the months (P<0.05). The averages of surface temperatures were RT=38.2±0.5°C, ORB=36.1±0.8°C, LF=33.5±2.5°C, RF=35.4±1.7ºC and SCR=33.3±1.1°C, which exhibited significant differences for shifts and throughout the months (P<0.05). Positive correlations were obtained between THI and ORB (0.72), RF (0.77), LF (0.75) and SCR (0.41) (P<0.0001). The maximum temperature of ORB showed the highest correlation with RT (0.58, P<0.0001). Therefore, the surface temperatures are subject to climatic variations and increase throughout the day, due to the variation in thermal comfort indexes, and the maximum ORB temperature was the parameter most related to rectal temperature. Lastly, the results indicate that IRT may be a useful non-invasive and accurate tool to detect the variations in ORB, LF, RF and SCR temperature in buffalo bulls.

Lessons from reproductive technology research

A plethora of assisted reproductive technologies (ARTs) have come into routine use over the past half century. Some of these procedures were used much earlier experimentally. For example, Spallanzani performed artificial insemination in the dog in the late 1700s, and Heape did successful embryo transfer in the rabbit in 1890. Truly revolutionary tools and concepts important for ART occur at approximately half-decade intervals, for example, recombinant DNA procedures, transgenic technology, somatic cell nuclear transplantation, the polymerase chain reaction, and microRNAs. Similarly, obvious technologies sometimes take decades to come into practical use, such as sexing sperm and in vitro fertilization. I have categorized ARTs into five somewhat arbitrary categories in terms of perceived difficulty and feasibility: (a) when the seemingly possible turns out to be (essentially) impossible, e.g., homozygous, uniparental females; (b) when the seemingly impossible becomes possible, e.g., cryopreservation of embryos and transgenesis; (c) when the seemingly difficult turns out to be relatively easy, e.g., cryopreservation of sperm; (d) when the seemingly easy turns out to be difficult in key species, e.g., in vitro fertilization; and (e) when the seemingly difficult remains difficult, e.g., making true embryonic stem cells. The adage that "it is easy when you know how" applies repeatedly. The boundaries between what appears impossible/possible and difficult/easy change constantly owing to new tools and insights, one of the more important lessons learned. ARTs frequently are synergistic with each other. For example, somatic cell nuclear transplantation has made many kinds of experiments feasible that otherwise were impractical. Another example is that sexing sperm is useless for application without artificial insemination or in vitro fertilization. ARTs frequently are perceived as neat tricks and stimulate further thinking. This is useful for both teaching and research.

Genome-wide association study for semen volume and total number of sperm in Holstein-Friesian bulls

In artificial insemination industry bulls producing high volume of semen with relatively high concentration of sperm are very desirable since they ensure stable production of commercial straws especially in case of top bulls. The aim of the study was to screen the entire bull genome to identify markers and candidate genes underlying semen volume (SV) and total number of sperm (TNS) in ejaculate produced by Holstein-Friesian bulls. Data on semen production were retrieved from records of AI center and included a population of 877 Holstein-Friesian bulls. Each bull was genotyped using the Illumina BovineSNP50 BeadChip. Genome-wide association analysis was performed with the use of GoldenHelix SVS7 software. An additive model for Linear Regression Analysis was used to estimate the effect of SNP marker for SV and TNS. After Bonferroni correction, 3 markers located on chromosome 22 reached the highest significance (rs41625599, rs41584616, rs42012507) for both traits. In the vicinity of these significant markers 3 genes are located (DCP1A, SFMBT1, TMEM110). Moreover, marker rs110109069 located on chromosome 25 was significantly associated with TNS and marker rs42438348 located on chromosome 10 has been found to be associated with SV. Some additional candidate genes were suggested to be potentially involved in analyzed traits (GALC, PRKCD, PHF7, TLR9, SPATA7). Identifying SNPs associated with the lower total number of sperm may be very useful for early recognition of a young sire as less suitable for effective semen production in artificial insemination centers.

Integrated evaluation of scrotal temperature and testosteronemia after GnRH administration in young bulls with low semen production

The aim of this study was to determine the suitability of thermographic monitoring of scrotal surface temperature (SST) as a method to monitor testicular function. Yearling bulls (n = 23) with low semen production were selected. Scrotal surface temperature and serum testosterone (T) concentrations were evaluated before and after administration of 10.5 μg buserelin acetate IV. Thermographic images of scrotum were recorded at 0, 15, 30, 45 and 60 min post-GnRH, while blood sampling was only performed at 60 min post-GnRH. Bulls were divided in two groups: LowTemp bulls (n = 10) had a decreased SST at 60 min; HighTemp bulls (n = 13) had an increased SST. After 60 min, LowTemp bulls had higher T concentrations compared to HighTemp bulls: 14.32 ng/ml ± 0.53 vs 10.30 ± 1.37 ng/ml (mean ± SEM; p < 0.05), respectively. Reproductive performances in both groups improved after GnRH administration, resulting in an increased number of inseminating doses from each collection, which was higher in LowTemp bulls. Pearson correlation test showed a negative relationship between T and SST (r = -0.554). In conclusion, a decreased scrotal surface temperature 60 min after GnRH treatment was associated with improved semen production.