Genome-wide association study for growth traits in Nelore cattle.

The objective of this study was to investigate the association of single nucleotide polymorphisms (SNPs) with birth weight, weight gain from birth to weaning and from weaning to yearling, yearling height and cow weight in Nelore cattle. Data from 5064 animals participating in the DeltaGen and PAINT breeding programs were used. The animals were genotyped with a panel of 777 962 SNPs (Illumina BovineHD BeadChip) and 412 993 SNPs remained after quality control analysis of the genomic data. A genome-wide association study was performed using a single-step methodology. The analyses were processed with the BLUPF90 family of programs. When applied to a genome-wide association studies, the single-step GBLUP methodology is an iterative process that estimates weights for the SNPs. The weights of SNPs were included in all analyses by iteratively applying the single-step GBLUP methodology and repeated twice so that the effect of the SNP and the effect of the animal were recalculated in order to increase the weight of SNPs with large effects and to reduce the weight of those with small effects. The genome-wide association results are reported based on the proportion of variance explained by windows of 50 adjacent SNPs. Considering the two iterations, only windows with an additive genetic variance >1.5% were presented in the results. Associations were observed with birth weight on BTA 14, with weight gain from birth to weaning on BTA 5 and 29, with weight gain from weaning to yearling on BTA 11, and with yearling height on BTA 8, showing the genes TMEM68 (transmembrane protein 8B) associated with birth weight and yearling height, XKR4 (XK, Kell blood group complex subunit-related family, member 4) associated with birth weight, NPR2 (natriuretic peptide receptor B) associated with yearling height, and REG3G (regenerating islet-derived 3-gamma) associated with weight gain from weaning to yearling. These genes play an important role in feed intake, weight gain and the regulation of skeletal growth.

Genetic associations between scrotal circumference and female reproductive traits in Nelore cattle.

The objective of this study was to estimate genetic associations between scrotal circumference obtained at 12 (SC12; mean of 21.46 ± 2.74 cm), 15 (SC15; mean of 25.31 ± 3.19 cm), and 18 mo of age (SC18; mean of 26.77 ± 2.95 cm) and reproductive traits measured directly in heifers (age at first calving [AFC]: mean of 1,062.06 ± 114.79 d; heifer pregnancy at 16 mo of age [HP]: mean of 15.4 ± 0.36%; and subsequent rebreeding of primiparous heifers [HR]: mean of 27.1 ± 0.44%) using Bayesian inference to evaluate the possible inclusion of these traits as selection criteria in beef cattle breeding programs. Genetic gains comparisons were also estimated. A total of 53,683 data of Nelore animals born between 1990 and 2006, obtained from the livestock archive of Agropecuária Jacarezinho Ltda. (Valparaíso, São Paulo, Brazil), were analyzed. Two-trait analysis provided heritability estimates of 0.35 ± 0.08, 0.40 ± 0.04, 0.37 ± 0.03, 0.21 ± 0.01, 0.55 ± 0.03, and 0.17 ± 0.03 for SC12, SC15, SC18, AFC, HP, and HR, respectively. The genetic correlations between scrotal circumference and AFC, HP, and HR were -0.42 ± 0.12, 0.43 ± 0.13, and -0.13 ± 0.17, respectively, for SC12; -0.25 ± 0.07, 0.26 ± 0.07, and -0.11 ± 0.10, respectively, for SC15; and -0.22 ± 0.06, 0.39 ± 0.06, and 0.11 ± 0.09, respectively, for SC18. The direct selection response for HP was 0.12%, but when HP is indirectly selected based on the scrotal circumferences, the gains on these correlated responses were higher (0.16, 0.16, and 0.22%) for selection based on SC12, SC15, and SC18, respectively. These findings suggest that the selection of animals for larger scrotal circumference, particularly at 12 mo of age, should result in higher rates of HP and younger AFC of Nelore females.

Evaluation of productivity of sexually precocious Nelore heifers.

The objectives of the present study were to investigate the influence of yearling weight on the occurrence of early pregnancy and to determine differences between precocious and non-precocious heifers in terms of pre- and postnatal calf mortality, calf weight and height, mature cow weight, and stayability of the cow in the herd. Data from 26 977 females of a Nelore herd that participated in the breeding season between 1986 and 2004 were analyzed. The influence of yearling weight on sexual precocity and differences between precocious and non-precocious heifers in pre- and postnatal calf mortality and stayability were analyzed using the GENMOD procedure of the SAS program. Differences in the growth traits between precocious and non-precocious animals were estimated by contrast analysis. Three groups were analyzed for postnatal mortality: first calving of the heifers, calves born from the third calving and all offspring of the cow. In order to have a standardized calving to conception period for all females (precocious and non-precocious), calves born from the second calving were not included in the analysis. This was necessary because the first calving to conception period (days open) of precocious heifers was longer than for non-precocious due to farm reproductive management. No differences in postnatal mortality rates, from the third calving, were observed between the two groups of heifers studied. Analysis of all offspring of the dams showed a 9% higher probability of death of calves born to precocious heifers compared with calves born to non-precocious heifers. With respect to stayability, precocious heifers presented 33% greater odds to remain in the herd until 5 and 6 years of age and 28% greater odds to remain in the herd until 7 years when compared with non-precocious heifers. Precocious heifers weaned calves (205 days) significantly heavier than non-precocious ones, 1.410 and 0.797 kg considering the weaning weights of all offspring and of the third calving, respectively. With respect to sexual precocity, the results suggest that the probability of heifers to become pregnant at 16 months of age increases with increasing weight. However, heifers weighing more than 240 kg present practically the same pregnancy probability. Nevertheless, exposure of heifers during the early breeding season is recommended for beef cattle herds raised in tropical regions in view of the numerous benefits demonstrated here.