Utilization of free lysine by growing pigs.

1. The results of nine estimates of the efficiency of utilization of supplements of free lysine by growing pigs fed once daily and reported by Batterham (1974) and Batterham & O'Neill (1978) were re-analysed using carcass rather than live-weight values as the criteria of response. 2. The efficiency of utilization of free lysine with once daily feeding relative to frequent feeding was 0.53 using carcass gain as the criterion of response (P less than 0.001), and 0.56 using food conversion efficiency on a carcass basis (P less than 0.001). These estimated were lower than estimated of 0.67 using live-weight gain (P less than 0.01) and 0.77 using food conversion ratio on a live-weight basis (P less than 0.05). 3. The results indicate that current estimates of the lysine requirements of pigs that are based on responses to supplements of free lysine under once daily feeding regimens may be 10-30% over-estimated, as a result of incomplete utilization of the free lysine.