The effect of commercially formulated, reduced crude protein diets, formulated to 11 apparent ileal digestible essential amino acids, on nitrogen retention by growing and finishing boars

Abstract

Two experiments were carried out to determine the nitrogen retention (NR) and gross efficiency of NR (NR/NI) of boars offered diets with reduced crude protein (CP) levels designed to decrease nitrogen excretion. Six diets were compared which differed in CP content, from 177 to 253 g/kg and from 151 to 229 g/kg for growing and finishing boars, respectively. All diets were isocaloric and formulated to minimum amounts of all 11 essential amino acids on a determined apparent ileal digestible basis (IEAA), calculated from the lysine:IEAA ratio required for Ideal Protein (IP). Formulating the diets to all 11 IEAA was not sufficiently accurate to maintain dietary IP content at the lowest CP levels (177 and 151 g/kg). These two diets significantly increased NR/NI for the boars ( P<0.01) but this was not sufficient to maintain NR which was reduced in both the growing (13%; P<0.05) and the finishing (26%; P<0.001) boars. The two lowest CP diets also had a lower dietary electrolyte balance (dEB) which could have contributed to the reduction of NR.