Assessment of DGAT1 and LEP gene polymorphisms in three Nelore (Bos indicus) lines selected for growth and their relationship with growth and carcass traits

The aim of this study was to analyze LEP and DGAT1 gene polymorphisms in 3 Nelore lines selected for growth and to evaluate their effects on growth and carcass traits. Traits analyzed were birth, weaning, and yearling weight, rump height, LM area, backfat thickness, and rump fat thickness obtained by ultrasound. Two SNP in the LEP gene [LEP 1620(A/G) and LEP 305(T/C)] and the K232A mutation in the DGAT1 gene were analyzed. The sample consisted of 357 Nelore heifers from 2 lines selected for yearling weight and a control line, established in 1980, at the Estacao Experimental de Zootecnia de Sertaozinho (Sertaozinho, Brazil). Three genotypes were obtained for each marker. Differences in allele frequencies among the 3 lines were only observed for the DGAT1 K232A polymorphism, with the frequency of the A allele being greater in the control line than in the selected lines. The DGAT1 K232A mutation was associated only with rump height, whereas LEP 1620(A/G) was associated with weaning weight and LEP 305(T/C) with birth weight and backfat thickness. However, more studies, with larger data sets, are necessary before these makers can be used for marker-assisted selection.

Human-animal interaction, stress, and embryo production in Bos indicus embryo donors under tropical conditions

This study investigated the effect of human-animal interaction (HAI) and the stress response on the quality of embryo production in superovulated Nelore (Bos indicus) cattle, under tropical conditions. Thirty-two females underwent a superovulation protocol for 5 days. Cortisol concentrations were determined in blood plasma collected on days 0, 4, and 5. Artificial insemination was performed on days 4 and 5, and nonsurgical embryo flushing on day 11. Embryo production and viability were determined. Human stimulation, animal behaviors, accidents, and handling time were recorded to assess HAI. Cattle age was negatively correlated with accidents, frequency of aversive behaviors, and negative stimuli by stockperson during transit through corral compartments to receive superovulation treatments. The factor analysis revealed two distinct groups. The first group was called stressed and had higher cortisol concentration than the nonstressed group, 16.0 +/- 2.1 and 12.5 +/- 1.0 ng/mL, respectively. Comparisons between these groups showed that the frequency of voice emissions by the stockperson and the number of accidents were higher in the stressed group, and also, the mean handling time was longer in the stressed group than for the nonstressed. As a result, viability rate of the embryos was 19% lower in the stressed group (P < 0.05). This indicates that intensive negative HAI is likely related to stress, which affects embryo production in a superovulation program.

Testicular traits as selection criteria for young Nellore bulls

The objective of this study was to evaluate the possible use of biometric testicular traits as selection criteria for young Nellore bulls using Bayesian inference to estimate heritability coefficients and genetic correlations. Multitrait analysis was performed including 17,211 records of scrotal circumference obtained during andrological assessment (SCAND) and 15,313 records of testicular volume and shape. In addition, 50,809 records of scrotal circumference at 18 mo (SC18), used as an anchor trait, were analyzed. The (co) variance components and breeding values were estimated by Gibbs sampling using the Gibbs2F90 program under an animal model that included contemporary groups as fixed effects, age of the animal as a linear covariate, and direct additive genetic effects as random effects. Heritabilities of 0.42, 0.43, 0.31, 0.20, 0.04, 0.16, 0.15, and 0.10 were obtained for SC18, SCAND, testicular volume, testicular shape, minor defects, major defects, total defects, and satisfactory andrological evaluation, respectively. The genetic correlations between SC18 and the other traits were 0.84 (SCAND), 0.75 (testicular shape), 0.44 (testicular volume), -0.23 (minor defects), -0.16 (major defects), -0.24 (total defects), and 0.56 (satisfactory andrological evaluation). Genetic correlations of 0.94 and 0.52 were obtained between SCAND and testicular volume and shape, respectively, and of 0.52 between testicular volume and testicular shape. In addition to favorable genetic parameter estimates, SC18 was found to be the most advantageous testicular trait due to its easy measurement before andrological assessment of the animals, even though the utilization of biometric testicular traits as selection criteria was also found to be possible. In conclusion, SC18 and biometric testicular traits can be adopted as a selection criterion to improve the fertility of young Nellore bulls.