Effects of low protein diets on performance of pigs with a lean genotype between 40 and 115 kg liveweight

The aim of the work was to assess the effects of three dietary protein regimes on pig performance and nitrogen (N) excretion, in particular, whether performance can be maintained in lean, fast growing pigswhenprotein levels are reduced to limitNexcretion. Entire male pigs of a lean genotype (Pietrain ·Large White·Landrace), 192 in total in four batches, were grown from 40 to 115 kg in pens with four pigs per pen. The diets were: (i) a high-protein control regime; (ii) a low-protein regime in which protein was reduced by ~2 percentage units in each growth stage, but with levels of five essential amino acids the same as in the control (LP1); (iii) an even lower protein regime in which levels of essential amino acids were not maintained beyond 60 kg (LP2). The LP2 regime was designed to promote intramuscular fat deposition rather than efficient growth. Excretion of N was reduced by 17% and 19% in LP1 and LP2, respectively, compared with the control. Average daily gain was lower and feed conversion ratio higher in LP2 than the other regimes, as expected. The control and LP1, which differed in protein but not essential amino acid levels, produced broadly similar results for performance, but pigs in LP1 had poorer feed conversion than control pigs, which could be due to slightly greater fat deposition. The results show the difficulty in maintaining consistently high levels of performance in fast-growing, lean pigs when dietary protein levels are reduced.