2.2. Animal Management

Four hundred 15–18-month-old weaned tropical composite steers of crossbred Bos indicus and Bos taurus genotypes, weighing 320 ± 21 kg as the initial average liveweight, were utilised in this set-stocked 147-day grazing trial. Prior to the experiment, the steers were grazing on buffel grass-dominated pastures. Experimental steers were randomly assigned to either of the two pastures, buffel grass only (n = 200) or mixed buffel grass-Desmanthus pastures (n = 200) at 2.87 and 2.60 ha/steer stocking rate, respectively, based on the farm manager’s long knowledge of the paddocks’ carrying capacity and remained constant throughout the trial period. Steers were not supplemented throughout backgrounding and were weighed on days 0, 49, 79 and 147 after the onset of grazing. Steers were brought from the paddocks at 09:00 h, left in the holding yards for one hour and weighed between 10:00 h and 14:00 h. Unfasted weights were recorded automatically (Gallagher 65 Scanlon Drive, Epping, Victoria 3076, Australia) and the average daily weight gain (ADG) was calculated by regression using the four weigh points. An a priori power analysis using G-Power was conducted to determine the appropriate sample size (Figure 1). A total sample size of 50 steers was required to achieve statistical power of 80% with a critical F-value of 4.0 for a large effect size and a significance level of 0.05. Therefore, twenty-five steers per paddock were randomly selected on day 0 for body condition (BCS) scoring using a five-point scoring system (1–5) [30] and faecal samples taken in parallel with the weighing session. Blood samples were collected from these same 50 steers during days 0 and 147 weighing sessions.

G-Power analysis for statistical power, critical F-value and sample size.