Estimates of Genetic Correlations between Live Ultrasound Scan Traits and Days to Calving in Hereford Cattle

Restricted maximum likelihood estimates of genetic correlations between between live ultrasound scan measurements and days to calving were obtained from bivariate analyses. Scan traits considered were fat depth at the 12/13−th rib, P8 fat depth, percentage intramuscular fat and eye muscle area, treating records for heifers or steers and bulls as separate traits. Analyses were carried out including all days to calving records, and considering the subset of cows only which had a ’complete sequence’ of records, beginning with a first mating record. Heritability estimates for days to calving were low, about 3% with a repeatability of 18%. Estimates of genetic correlations were low to moderate, and consistently negative for fat depth measurements, i.e. animals with a higher genetic potential for fat deposition tended to have better reproductive performance.