A note on the effects of variations in food intake on nitrogen retention in control and selection lines of Large White pigs

Fifty-three 7-day nitrogen balances were made using 13 control (C) and 15 selection line (S) Large White boars. Six feeding treatments were imposed, ranging from a Jevel estimated to maintain weight to a level aimed at inducing a fast growth rate from giving food twice daily to appetite for 30 min. Nitrogen retention did not differ significantly, but C boars retained slightly more than S boars at the lowest food intake, while S boars retained Slightly more than C boars at higher food intakes. The slopes of the regression of nitrogen retention against food intake for growth was steeper for S than for C boars (P > 0·05). It is concluded that great care should be taken in using metabolism experiment results to predict changes in body composition.