The overall objective of this research was to evaluate impacts on growth of Droughtmaster cattle in northern Queensland based on four years (2009-2012) of repeated weight records from a single operation. Animals (total records n = 1,717) were identified by management group (n = 43). Gender consisted of females (n = 786), bulls (n = 386), and steers (n = 545). Age at weight evaluation varied substantially across management groups and was therefore nested within each management group to create a 90-day window. Age, sire, and age of dam, impacted (P < 0.001) weights taken at branding, and, sire and age showed significance at every weight taken (P < 0.001). Age of dam was significant for weaning weight (P = 0.002), but became irrelevant for yearling (P = 0.7252) and final (P = 0.1423) weights. Heritability values for branding, weaning, yearling, and final weight were calculated from estimates of sire variance to be 0.35, 0.42, 0.23, and 0.49, respectively. Heritability values of weight gain from birth to branding, branding to weaning, weaning to yearling, and yearling to final weights were estimated to be 0.23, 0.09, 0.26, and 0.29, respectively. Simple correlations among these traits were evaluated within gender. Female, bull, and steer weights were moderate to highly correlated (0.53-0.77, 0.49-0.85, and 0.70-0.91 respectively). Ranges in correlations were mostly high depending on gender (females 0.68-0.92, bulls 0.53-0.81, and steers 0.70-0.91). Correlations between age and weight varied in strength depending on sex (females, 0.53-0.77; bulls, 0.24-0.79;, steers, 0.48-0.81). Correlations were stronger for traits measured closer in time, and for steers compared to bulls and females. Results correspond to previous reports in numerous breeds. Sire, calf age, and age of dam significantly impact animals' growth during pre-weaning stages; however, influences of these effects were not identical across all genders. The last weight, which was closest to maturity, showed to be the most heritable in these data. Differences seen across genders for later weights can arise from different management strategies, including sire selection and supplementation, and it is possible shapes bend of growth curves may be manipulated, but there is a set mature size.
ETD Chair
Skaggs, Chris Associate Vice Chancellor and Associate Dean
