Effect of plane of nutrition during the first 12 weeks of life on growth, metabolic and reproductive hormone concentrations, and testicular relative mRNA abundance in preweaned Holstein Friesian bull calves

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.

Review: Early and late determinants of puberty in ruminants and the role of nutrition

This article reviews the scientific literature on puberty with a focus on ruminants and draws inference, where appropriate, from recent findings in transgenic mouse models and human pathology. Early genetic determinants of puberty have been discovered in humans suffering from hypogonadotropic hypogonadism or central precocious puberty. Transgenic mouse models selected on the basis of the causative defective genes helped in discovering the cellular and molecular mechanisms involved. Most of the genes found are involved in the development of neuroendocrine networks during embryo development and early postnatal life. Notwithstanding that the development of neuroendocrine networks takes place early in puberty, a delay or acceleration in the development of Gonadotropin Releasing Hormone (GnRH) neurons has an impact on puberty onset inducing a delay or an advance, respectively. Among the genes discovered in humans and laboratory models, only a few of them displayed polymorphisms associated with advanced sexual maturity, but also marbling, growth traits and callipygian conformation. This could be related to the fact that rather than puberty onset, most research monitored sexual maturity. Sexual maturity occurs after puberty onset and involves factors regulating the maturation of gonads and in the expression of sexual behaviour. The association with growth and metabolic traits is not surprising since nutrition is the major environmental factor that will act on late genetic determinants of puberty onset. However, a recent hypothesis emerged suggesting that it is the postnatal activation of the GnRH neuronal network that induces the acceleration of growth and weight gain. Hence, nutritional factors need the activation of GnRH neurons first before acting on late genetic determinants. Moreover, nutritional factors can also affect the epigenetic landscape of parental gamete's genome with the consequence of specific methylation of genes involved in GnRH neuron development in the embryo. Season is another important regulator of puberty onset in seasonal small ruminants and appears to involve the same mechanisms that are involved in seasonal transition in adults. The social environment is also an underestimated factor affecting puberty onset in domestic ruminants, most research studies focused on olfactory cues, but the genetic basis has not heretofore been adequately tackled by the scientific community. Additionally, there is some evidence to suggest transgenerational effects exist, in that nutritional and social cues to which parents were exposed, could affect the epigenetic landscape of parental gametes resulting in the epigenetic regulation of early genetic determinants of puberty onset in their offspring.

Genome-wide association study reveals candidate markers related to field fertility and semen quality traits in Holstein-Friesian bulls

In vitro assessment of bull semen quality is routinely used in bull semen processing centres in order to ensure that semen destined to be used in the field has passed minimum standards. Despite these stringent quality control checks, individual bulls that pass the quality control checks can still vary in field fertility by up to 25%. A genome-wide association study was undertaken to determine genetic markers associated with prefreeze and post-thaw bull sperm quality traits as well as field fertility. Genome-wide association analysis was performed using a single nucleotide polymorphism (SNP) regression mixed linear model in WOMBAT. Genes within a 250 Kb span of a suggestive (P ≤ 1 × 10^-5) SNP were considered as candidate genes. One SNP was associated with adjusted pregnancy rate, and 21 SNPs were associated across the seven semen quality traits (P ≤ 1 × 10^-5). Functional candidate genes include SIPA1L2 which was associated with adjusted pregnancy rate. This encodes a Rap GTPase-activating protein involved in Rap1 signalling pathway and was previously found to play a role in the process of sperm differentiation. Gene ontology (GO) analysis also identified significantly enriched biological processes involved protein tyrosine kinase activity including genes such as DYRK1A, TEC and TXK that were associated with sperm motility prior to freezing. Another candidate gene associated with post-thaw sperm motility was FHDC1 which coordinates actin filament and microtubule dynamics. The induced 11 GO terms in the ejaculates rejected after freezing trait were related to ATPase, phosphatase and hydrolase activity. These results reveal novel specific genomic regions and candidate genes associated with economically important phenotypes such as field fertility and semen quality traits.

Early life nutrition affects the molecular ontogeny of testicular development in the young bull calf

Enhanced early life nutrition accelerates sexual development in the bull calf through neuroendocrine-signalling mediated via the hypothalamic-pituitary-testicular axis. Our aim was to assess the impact of contrasting feeding regimes in bull calves during the first 12 weeks of life on the testes transcriptome and proteome. Holstein-Friesian bull calves were offered either a high (HI) or moderate (MOD) plane of nutrition, designed to support target growth rates of 1.0 and 0.5 kg/day, respectively. At 12 weeks of age all calves were euthanized, testicular parenchyma sampled, and global transcriptome (miRNAseq and mRNAseq) and proteome analyses undertaken. Bioinformatic analyses revealed 7 differentially expressed (DE) miRNA and 20 DE mRNA. There were no differentially abundant proteins between the two dietary groups. Integration of omics results highlighted a potential role for the cadherin gene, CDH13, in earlier reproductive development. Furthermore, co-regulatory network analysis of the proteomic data revealed CDH13 as a hub protein within a network enriched for processes related to insulin, IGF-1, androgen and Sertoli cell junction signalling pathways as well as cholesterol biosynthesis. Overall, results highlight a potential role for CDH13 in mediating earlier reproductive development as a consequence of enhanced early life nutrition in the bull calf.

Multifaceted Interplay among Social Dominance, Body Condition, Appetitive and Consummatory Sexual Behaviors, and Semen Quality in Dorper Rams during Out-Of-Season and Transition Periods

Dorper rams (n = 24) were evaluated during the sexual resting season to determine their social rank (SR), either high (HSR) or low (LSR), under intensive management conditions in northern Mexico (25° N). Aggressive behaviors were quantified during male-to-male interactions, and appetitive and consummatory sexual behaviors during male-to-female interactions. Morphometric, live weight (LW), and body condition score (BCS) were recorded. During the early reproductive season, male-to-female behaviors were newly itemized simultaneously by seminal quality and quantity sampling. Finally, the dependent variables of the hemogram components were also quantified. Neither LW (61.25 ± 2.4 kg) nor morphometric variables differed between SR groups. However, BCS (2.25 vs. 2.66 u), sexual behaviors (i.e., approaches: 59.6 vs. 21.73 n, mating with ejaculation: 77.7 vs. 42.86 %, latency to ejaculation: 16.6 vs. 143.07 s), ejaculate volume (0.57 vs. 0.23 mL), and hemogram components favored the HSR rams (p < 0.05). Moreover, in their first male-to-female interaction, >50% of the LSR rams failed to display any sexual activity. HSR rams displayed a greater number of threatening behaviors, managing to displace LSR rams when exposed to estrus ewes during the male sexual resting season; more sexual behaviors; and an increased seminal volume in a non-live weight-dependent fashion.

Gene co-expression networks contributing to reproductive development in Holstein-Friesian bull calves

Enhanced early life nutrition stimulates the functionality of the hypothalamic-pituitary-testicular (HPT) biochemical signalling axis, resulting in precocious reproductive development in bull calves. Additionally, there is evidence that peptides and hormones produced within adipose tissue depots are also central in mediating the effect of metabolic status with reproductive development. The objective of this study was to undertake gene co-expression analyses on transcriptional data of the HPT and adipose tissues derived from bull calves fed contrasting planes of nutrition up to 18 weeks of life. The relationship between networks of co-expressed genes in each tissue dataset with calf phenotypic data was also assessed using a Pearson correlation analysis. Phenotypic data were related to metabolic status (systemic concentrations of insulin, leptin, adiponectin and IGF-1) reproductive development (systemic concentrations of testosterone, FSH and LH) and markers of testicular development (seminiferous tubule diameter, seminiferous tubule lumen score, spermatogenic cells and Sertoli cells). In the hypothalamus, gene co-expression networks involved in biochemical signalling processes related to gonadotropin-releasing hormone (GnRH) secretion were positively associated (P < 0.05) with systemic concentrations of IGF-1 and insulin. Similarly, a network of gene transcripts involved in GnRH signalling in the anterior pituitary was positively associated (P < 0.05) with systemic concentrations of LH. In the testes and adipose tissues, networks of co-expressed genes implicated in cholesterol and fatty acid biosynthesis were positively associated (P < 0.05) with lumen score, Sertoli cell number, and stage of spermatogenesis. Additionally, gene co-expression networks significantly associated (P < 0.05) with both metabolic and reproductive trait data were found to be enriched (P < 0.05) for biological pathways related to energy production, cellular growth and proliferation, GnRH signalling and cholesterol biosynthesis across multiple tissues examined. Results from this study highlight networks of co-expressed genes directly associated with markers of enhanced metabolic status and subsequent earlier reproductive development. Furthermore, genes involved in biological processes mentioned above may hold potential for informing genomic selection breeding programmes for the selection of calves capable of displaying earlier reproductive development as a consequence of enhanced dietary intake.

The Distribution, Expression Patterns and Functional Analysis of NR1D1 and NR4A2 in the Reproductive Axis Tissues of the Male Tianzhu White Yak

Nuclear hormone receptors NR1D1 and NR4A2 play important roles in the synthesis and metabolism of hormones that are thought to be strictly regulated by the hypothalamus-pituitary-gonad axis (HPG) tissues via gene expression. However, in the yak, the function and regulatory mechanisms of NR1D1 and NR4A2 are not clearly understood. The current study is aimed to investigate the expression patterns, distribution and functions of these two receptors in HPG tissues in male Tianzhu white yaks. Immunohistochemical staining showed NR1D1 and NR4A2 proteins were present in all yak HPG tissues with differential expression patterns and degrees of staining, particularly in Leydig cells that were strongly positive in accordance with the immunofluorescence results. qRT-PCR and Western blot results suggested that the highest expression levels of NR1D1 and NR4A2 mRNA were present in the hypothalamus, while the expression levels of NR1D1 and NR4A2 proteins were higher in the testis and epididymis than in the hypothalamus or pituitary gland. In addition, expression levels of NR1D1 and NR4A2 mRNA and protein in testicular tissues differed by age. Expression levels were significantly higher at 6 years of age. Gene ontology (GO) and pathway analysis enrichment revealed that NR1D1 may directly regulate the synthesis and metabolism of steroid hormones via interaction with different targets, while NR4A2 may indirectly regulate the synthesis and metabolism of steroid hormones. These results showed that NR1D1 and NR4A2, as important mediators, are involved in the regulation of male yak reproduction, and especially of steroid hormones and androgen metabolism. These results will be helpful for the further understanding of the regulatory mechanisms of NR1D1 and NR4A2 in yak reproduction.