Nutritional and genomic control of sexual maturation in the bull

Holstein Friesian bull calves were assigned to either a high (HI) or moderate (MOD) diet and fed milk replacer and concentrate to achieve growth rates of at least 1.0 and 0.5 kg/day, respectively. Animal growth performance, feed intake, and systemic concentrations of metabolites, metabolic and reproductive hormones were assessed. Pulsatility of reproductive hormones was recorded at 15 min intervals during a 10-hour period at 10 weeks old. At 87 ± 2.14 days of age, calves were euthanized, testes weighed and testicular tissue harvested. Differential expression of mRNA candidate genes involved in testicular development was examined using qPCR assays. Calves offered HI had greater mean slaughter weight and testicular tissue weight than MOD. Relative mRNA abundance data indicated advanced testicular development through up-regulation of genes involved in cellular metabolism, cholesterol biosynthesis, testicular function and Sertoli cell development in HI compared with MOD calves. The testicular parenchyma was sampled, and global transcriptome and proteome analyses was undertaken. Bioinformatic analyses of omics data revealed 7 differentially expressed (DE) miRNA and 20 DE mRNA. There were no differentially abundant proteins between the two dietary groups. Enrichment of processes involved in Sertoli cell development, as well as androgen and AMPK signalling was apparent from the DE mRNA, emphasizing the effect of enhanced early life nutrition on testicular development. Integrative analysis highlighted a role for CDH13, in earlier reproductive development, through differential expression of both miR-2419-5p and CDH13. Furthermore, co-regulatory protein network analysis revealed CDH13 as a hub protein within a network for processes related to insulin, IGF-1, androgen and Sertoli cell junction signalling pathways and cholesterol biosynthesis. The second study assessed the variation in reproductive development and semen characteristics in young early post pubertal Holstein-Friesian (HF) bulls (n=1,117). Spring born HF bulls with a mean age and liveweight of 394 days and 412 kg, respectively, located on eight Irish commercial herds were enrolled in the study. Liveweight and scrotal circumference were measured on each animal and semen was collected using electroejaculation on a once off basis at 13 months old. Fresh semen characteristics were assessed using computer aided semen analysis including. Volume was also recorded, and total sperm number was generated. Morphology was assessed subjectively. Heritability estimates were calculated. Mean (SD) SC was 32.6 (2.15) cm. For SC values of >28cm for puberty, 98.37% of the bulls in this population reached this threshold. Approximately 88.5% of the bulls had >70% morphologically normal sperm. Mean heritability estimates of all traits was between 0.01 and 0.66, with SC, LW and normal sperm morphology displaying the largest heritabilites of 0.66, 0.28 and 0.22. Results highlight the large phenotypic and genetic variation in a range of semen quality traits, some of which were found to be highly heritable. A GWAS was carried out to screen the entire bovine genome for genetic variants associated with scrotal measurements as well as both semen quality and quantity characteristics in ejaculates produced by these early post pubertal HF bulls. Data on physical and semen quality characteristics were recorded from this population. Low-pass genome sequencing was conducted, and the sequence data were aligned to the ARS-UCD1.2 genome and missing genotypes where imputed. 16,929 suggestively significant SNPs were detected in the traits. The distribution of these SNPs suggests that most of the effects on the traits of interest were dispersed across all autosomes. 13 QTLs were associated with both the physical and semen traits examined and were located close to genes of interest including: CFAP52, MBD3L1, TMEM95, SPEM1, DLD, RIMS1, TEX10 LRRC18, H2BC1, RND3, CDH18, PRKCB and FNDC1.