The effect of screen size when grinding the roughage component in shipping pellets for export sheep.

Export wethers (30) in single pens were offered, over a 4 week period, 1 of 5 pelleted diets (6 sheep/diet) prepared to meet the National Standards for Livesheep Export but with the roughage component ground through different screen sizes. Feed intake increased (P < 0.05) from about 1400 g/day to 1530-1600 g/day as the size of the screen increased from 9-12 mm to 15 -20 mm. Weight gain for the sheep on the larger screen size diets was also 40-60 g/day greater (P < 0.05) than for those on the smaller screen sizes. While intake increased, digestibility of the diets did not change and was similar over the 4 weeks of the experiment and over all diets (57 + 0.5%). In 20 sheep (5/treatment) over 120 h following dosing with Cr-mordanted samples of the roughage component of 4 of the diets (9, 12, 15, 17 mm), Cr excretion rates were the same, indicating similar rumen turnover rates for these diets. The good growth performance of the sheep in this experiment compared to performance in previous experiments in this series, suggests that conditions of export have a large influence on efficiency of feed utilisation.