|
The genetics of heifer pubertal traits and their associations with female reproductive performance were estimated using records from 2,115 heifers representing 2 tropically adapted genotypes raised in northern Australia. Heifers were ultrasound scanned for ovarian activity every 4-6 weeks to determine the age at first observed corpus luteum (CL). Heifer live weight (WTCL) and ultrasound scanned fat depth (FATCL) were also recorded at this time. Heifers were mated at approximately 2 years of age and genetic and phenotypic relationships were estimated between days to calving (DC1), calving success (CS1) and age at first CL (AGECL). Results showed large genotype, location and birth month effects on age and fatness at first CL but not weight at first CL. Age at presence of the first CL (AGECL) was moderately to highly heritable: 0.57 and 0.52 for Brahmans and Tropical Composites, respectively. Other pubertal traits were also moderately heritable. Heritability estimates for DC1 and CS1, were 0.16 and 0.18 for Brahmans and 0.11 and 0.08 for Tropical Composites, respectively. DC1 and CS1 were genetically correlated with AGECL, particularly for Brahmans (0.87 and -0.58, respectively). Selection to improve first parity female reproductive performance is feasible in both genotypes, and for Brahmans AGECL could be used as an indirect selection criterion provided it can be measured cost effectively in industry. Associations with lifetime reproductive performance will be required before final recommendations can be made on recording and selection breeding schemes. |
|