Genome-Wide Association (GWAS) Applied to Carcass and Meat Traits of Nellore Cattle

The meat market has enormous importance for the world economy, and the quality of the product offered to the consumer is fundamental for the success of the sector. In this study, we analyzed a database which contained information on 2470 animals from a commercial farm in the state of São Paulo, Brazil. Of this total, 2181 animals were genotyped, using 777,962 single-nucleotide polymorphisms (SNPs). After quality control analysis, 468,321 SNPs provided information on the number of genotyped animals. Genome-wide association analyses (GWAS) were performed for the characteristics of the rib eye area (REA), subcutaneous fat thickness (SFT), shear force at 7 days' ageing (SF7), and intramuscular fat (IMF), with the aid of the single-step genomic best linear unbiased prediction (ssGBLUP) method, with the purpose of identifying possible genomic windows (~1 Mb) responsible for explaining at least 0.5% of the genetic variance of the traits under analysis (≥0.5%). These genomic regions were used in a gene search and enrichment analyses using MeSH terms. The distributed heritability coefficients were 0.14, 0.20, 0.18, and 0.21 for REA, SFT, SF7, and IMF, respectively. The GWAS results indicated significant genomic windows for the traits of interest in a total of 17 chromosomes. Enrichment analyses showed the following significant terms (FDR ≤ 0.05) associated with the characteristics under study: for the REA, heat stress disorders and life cycle stages; for SFT, insulin and nonesterified fatty acids; for SF7, apoptosis and heat shock proteins (HSP27); and for IMF, metalloproteinase 2. In addition, KEGG (Kyoto encyclopedia of genes and genomes) enrichment analysis allowed us to highlight important metabolic pathways related to the studied phenotypes, such as the growth hormone synthesis, insulin-signaling, fatty acid metabolism, and ABC transporter pathways. The results obtained provide a better understanding of the molecular processes involved in the expression of the studied characteristics and may contribute to the design of selection strategies and future studies aimed at improving the productivity of Nellore cattle.

Effect of nutrition on testicular traits of tropically adapted yearling beef bulls

The effects of different management practices on testicular development of young Bonsmara bulls fed a high energy (HE), medium energy (ME) and low energy (LE) diet after weaning were determined. Testicular histology and seminal traits were examined together with scrotal circumference (SC) development over an 84-day performance test trial period. The SC differed significantly (P < 0.001) between HE-, ME- and LE-fed bulls. Seminal traits, such as semen concentration were significantly (P < 0.001) lower in bulls fed the HE diet (1.3 ± 0.134) compared with those fed the ME diet (2.4 ± 0.18) and LE diet (2.6 ± 0.16). Similarly, linear movement of sperm was also affected by diet and movement was slower (P < 0.05) in bulls fed the HE diet (1.7 ± 0.30) compared with bulls fed the ME diet (2.2 ± 0.31) and LE diet (3.1 ± 0.23). The percentage total major (P < 0.001) and total minor (P < 0.05) sperm defects were also greater in the HE-fed bulls (27.1 ± 6.82 and 7.4 ± 0.91) compared with the ME-fed bulls (9.7 ± 1.45 and 5.5 ± 0.87) and for the LE-fed bulls (5.4 ± 1.26 and 3.9 ± 0.58). Dietary energy level (P < 0.05) influenced the percentage inactive seminiferous tubuli, with bulls fed the HE diet having 35% more seminiferous tubules classified as inactive compared with those bulls fed ME and LE diets. Scrotal fat deposits were higher (P < 0.05) in bulls fed the HE diet (243.4 ± 21.59 g) compared with those fed the ME (110.0 ± 12.1 g) and LE (88.4 ± 9.65 g) diets. Feeding HE diets to young bulls probably reduces their reproductive potential.