Application of longitudinal data analysis allows to detect differences in pre-breeding growing curves of 24-month calving Angus heifers under two pasture-based systems with differential puberty onset.

BACKGROUND: Longitudinal data analysis contributes to detect differences in the growing curve by exploiting all the information involved in repeated measurements, allowing to distinguish changes over time within individuals, from differences in the baseline levels among groups. In this research, longitudinal and cross-sectional analysis were compared to evaluate differences in growth in Angus heifers under two different grazing conditions, ad libitum (AG) and controlled (CG) to gain 0.5 kg day-1 . RESULTS: Longitudinal mixed models show differences in growing curve parameters between grazing conditions, that were not detected by cross-sectional analysis. Differences (P < 0.05) in first derivative of growth curves (daily gain) until 289 days were observed between treatments, AG being higher than CG. Correspondingly, pubertal heifer proportion was also higher in AG at the end of rearing (AG, 0.94; CG, 0.67). CONCLUSION: In longitudinal studies, the power to detect differences between groups increases by exploiting the whole information of repeated measures, modelling the relation between measurements performed on the same individual. Under a proper analysis, valid conclusion can be drawn with fewer animals in the trial, improving animal welfare and reducing investigation costs. © 2019 Society of Chemical Industry.

Association of a region of bovine chromosome 1 (BTA1) with age at puberty in Angus bulls.

Age at puberty is an important component of reproductive performance in cattle, so it is important to identify genes that contribute to the regulation of the onset of puberty and polymorphisms that explain differences between bulls. In a previous study, we found putative associations between age at puberty in Angus bulls and single-nucleotide polymorphisms (SNPs) in Chromosomes 1 and X. In the present work we aimed to confirm these findings in a larger sample of Angus bulls (n = 276). Four SNPs located in these regions were genotyped using SEQUENOM technology and the genotypes obtained were tested for association with age at puberty. The results showed that SNPs rs135953349 and rs110604205 on BTA1 were still significantly associated with age of puberty estimated at progressive sperm motility of 10% (P < 0.05). The association previously found on Chromosome X could not be confirmed. Analysis of the bovine genome revealed that the associated region (99.17-99.99 Mb) contained four predicted loci: myelodysplasia syndrome 1 (MDS1) and ecotropic virus integration site 1 (EVI1) complex locus (MECOM), eGF-like and EMI domain-containing 1 pseudogene-like (LOC100337483), microRNA mir-551b (MIR551B) and mCG140927-like (LOC100139843). The results obtained could contribute to the understanding of puberty regulation and could be useful for further identification and annotation of gene function in the context of reproduction.

Assessing the association of single nucleotide polymorphisms in thyroglobulin gene with age of puberty in bulls.

Puberty is a stage of sexual development determined by the interaction of many loci and environmental factors. Identification of genes contributing to genetic variation in this character can assist with selection for early pubertal bulls, improving genetic progress in livestock breeding. Thyroid hormones play an important role in sexual development and spermatogenic function. The objective of this study was to evaluate the association between single nucleotide polymorphisms (SNPs) located in thyroglobulin(TG) gene with age of puberty in Angus bulls. Four SNPs were genotyped in 273 animals using SEQUENOM technology and the association between markers and puberty age was analyzed. Results showed a significant association (P < 0.05) between these markers and puberty age estimated at a sperm concentration of 50 million and a progressive motility of 10%. This is the first report of an association of TG polymorphisms with age of puberty in bulls, and results suggest the importance of thyroidal regulation in bovine sexual development and arrival to puberty.

Association between GNRHR, LHR and IGF1 polymorphisms and timing of puberty in male Angus cattle.

BACKGROUND: In bovines, there are significant differences within and among beef breeds in the time when bulls reach puberty. Although the timing of puberty is likely to be a multigenic trait, previous studies indicate that there may also be single genes that exert major effects on the timing of puberty within the general population. Despite its economic importance, there are not many SNPs or genetic markers associated with the age of puberty in male cattle. In the present work, we selected three candidate genes, GNRHR, LHR and IGF1, and associated their polymorphisms with the age of puberty in Angus male cattle. RESULTS: After weaning, 276 Angus males were measured every month for weight (W), scrotal circumference (SC), sperm concentration (C) and percentage of motility (M). A total of 4 SNPs, two within GNRHR, one in LHR and one in IGF1 were genotyped using the pyrosequencing technique. IGF1-SnaBI SNP was significant associated (P < 0.01) with age at SC 28 cm, but it were not associated with age at M 10% and C 50 million. Genotype CC exhibited an average age at SC 28 cm of 7 and 11 days higher than CT (p = 0.037) and TT (p = 0.012), respectively. This SNP explained 1.5% of the genetic variance of age of puberty at SC28. LHR-I499L, GNRHR-SNP5 and GNRHR-SNP6 were not associated with any of the measurements. However, GNRHR haplotypes showed a suggestive association with age at SC 28 cm. CONCLUSIONS: The findings presented here could support the hypothesis that IGF1 is a regulator of the arrival to puberty in male calves and is involved in the events that precede and initiate puberty in bull calves. Given that most studies in cattle, as well as in other mammals, were done in female, the present results are the first evidence of markers associated with age at puberty in male cattle.

Animal markers assisted selection in South America: a point of view.

Genetic identification has been continuously evolving during the last century. The recent development of whole-genome projects allowed the discovery and characterization of a large number of single nucleotide polymorphisms (SNP). A number of high-throughput DNA methods has decreased the cost of DNA marker analysis and increased the amount of samples that can be processed at a time. Using this information and methods, many private and governmental laboratories offer a wide range of genetic tests, many of which have been patented. In the field of genetic resources, a significant amount of law-making has been developed at the international and regional levels. Many South American countries currently lack jurisprudence in relation to the protection of DNA sequences. In this paper, we compared laws related with life-form patents in some countries from South America. Nowadays, the knowledge and technology leveling of many of these countries allows marker assisted selection (MAS) programs to be applied. Herein, we resume the economical value of MAS. Finally, we present a point of view on the pertinence, viability and conditions for developing and applying MAS programs in South America.