Genetic Parameters of Age at Conception in Nellore Females Using Threshold Models.

Area of Science:

• Animal Science
• Genetics
• Reproductive Biology

Background:

• Optimizing Nellore female productivity is key for intensifying cattle production systems.
• Low heritability estimates for traits related to conception limit genetic progress.
• Accurate genetic parameter estimation is necessary for effective selection strategies.

Purpose of the Study:

• To evaluate genetic associations between weaning and yearling body weights and age at conception in Nellore females.
• To understand the genetic basis of reproductive efficiency in Nellore cattle.
• To inform selection criteria for improving conception success.

Main Methods:

• Utilized a mixed polychotomous threshold model suitable for categorical variables.
• Analyzed records from 796 Nellore females, treating body weights and age at conception as categorical variables.
• Estimated (co)variance components using Bayesian inference with a Gibbs sampler.

Main Results:

• Heritability estimates were 0.43 for weaning weight, 0.63 for yearling weight, and 0.19 for age at conception.
• High additive genetic correlation (0.79) was observed between weaning and yearling weights.
• Lower correlations were found between age at conception and weaning (-0.21) and yearling (0.34) weights.

Conclusions:

• Body weight alone is insufficient for selecting Nellore females with improved conception probability.
• Additional selective criteria beyond body weight are needed to enhance reproductive efficiency.
• Further research into genetic parameters influencing conception success is warranted.