Additive genetic relationships between scrotal circumference, heifer pregnancy, and stayability in Nellore cattle

Abstract

Scrotal circumference data from 47,605 Nellore young bulls, measured at around 18 mo of age (SC18), were analyzed simultaneously with 27,924 heifer pregnancy (HP) and 80,831 stayability (STAY) records to estimate their additive genetic relationships. Additionally, the possibility that economically relevant traits measured directly in females could replace SC18 as a selection criterion was verified. Heifer pregnancy was defined as the observation that a heifer conceived and remained pregnant, which was assessed by rectal palpation at 60 d. Females were exposed to sires for the first time at about 14 mo of age (between 11 and 16 mo). Stayability was defined as whether or not a cow calved every year up to 5 yr of age, when the opportunity to breed was provided. A Bayesian linear-threshold-threshold analysis via Gibbs sampler was used to estimate the variance and covariance components of the multitrait model. Heritability estimates were 0.42 ± 0.01, 0.53 ± 0.03, and 0.10 ± 0.01, for SC18, HP, and STAY, respectively. The genetic correlation estimates were 0.29 ± 0.05, 0.19 ± 0.05, and 0.64 ± 0.07 between SC18 and HP, SC18 and STAY, and HP and STAY, respectively. The residual correlation estimate between HP and STAY was -0.08 ± 0.03. The heritability values indicate the existence of considerable genetic variance for SC18 and HP traits. However, genetic correlations between SC18 and the female reproductive traits analyzed in the present study can only be considered moderate. The small residual correlation between HP and STAY suggests that environmental effects common to both traits are not major. The large heritability estimate for HP and the high genetic correlation between HP and STAY obtained in the present study confirm that EPD for HP can be used to select bulls for the production of precocious, fertile, and long-lived daughters. Moreover, SC18 could be incorporated in multitrait analysis to improve the prediction accuracy for HP genetic merit of young bulls.

Genetic relationship between growth and reproductive traits in Nellore cattle

“…The genetic correlation between SC and HP (0.30 6 0.03) was higher than the estimates reported by Eler et al 2004 and2006 (0.11 to 0.27) and similar to that reported by Van Melis et al (2010;0.29). The mean posterior genetic correlation between SC and STAY (0.17 6 0.04) differed from that reported by Silva et al (2006;0.27) and Evans et al (1999; estimate close to 0).…”

“…Nieto et al (2007) reported an estimate of 0.07 for Canchim animals (5/8 Charolais : 3/8 Nellore). Van Melis et al (2010) found a heritability of 0.10 6 0.01 for Nellore cattle belonging to the same herd as the animals studied in our experiment. The genetic gain obtained by selection for STAY is therefore expected to be small.…”

“…The mean posterior genetic correlation between SC and STAY (0.17 6 0.04) differed from that reported by Silva et al (2006;0.27) and Evans et al (1999; estimate close to 0). According to Van Melis et al (2010), SC does not show a strong genetic association with HP or STAY, and the response to selection based on the genetic merit for SC may be much slower than the response to selection based directly on genetic merit for HP. However, Eler et al (2004) showed the importance of the inclusion of SC data to increase the accuracy of the prediction of genetic merit for HP, especially in the case of young bulls for which there is still no information regarding HP of the daughters.…”

Characterization of the variable cow's age at last calving as a measurement of longevity by using the Kaplan–Meier estimator and the Cox model

“…Under such conditions, AFC may be negatively correlated with longevity, given that the younger heifers (born at the end of the birth season) have less probability to become pregnant at the end of the breeding season. However, Van Melis et al (2010) studied data from farms at which heifers were exposed to breeding at an early age (,14 months of age) and found a positive correlation (0.64) between heifer pregnancy and longevity. The longest interval between calvings occurs between the first and second calving (Werth et al, 1996).…”

Population structure and genetic trends for indigenous African beef cattle breeds in South Africa

“…Pereira et al (2008) reported the estimates of the annual genetic trend of breeding values of 0.98 kg for yearling weight and 0.27 kg for 18-month weight, respectively, for a Caracu beef herd. The available data for scrotal circumference indicated an increase in the trend, which has a positive implication for improved fertility, as scrotal circumference was found to have close relationships with spermatozoa quality and quantity in bulls and age at puberty in bulls' daughters (Kealey et al, 2006;Van Melis et al, 2010). The five breeds included in this study are not currently at risk of losing genetic diversity.…”