Amino acid digestibility and nitrogen utilization of high oil, high lysine, and waxy maize fed to growing pigs

Two experiments were conducted to determine the amino acid (AA) digestibility and nitrogen (N) utilization of three maize hybrids, i.e. high oil (HO), waxy (WX), and high lysine (HL) as compared to isogenic high oil (IHO), isogenic waxy (IWX), and a yellow dent (YD1) maize variety near-isogenic to HL. One yellow dent maize of unrelated genetics (YD2) was included as an additional control and to serve as a common treatment for cross-square comparison. In exp. 1, four castrates (initial BW: 52.8±1.7 kg) were equipped with T-cannulas in the distal ileum and used in two consecutive 4×4 Latin squares to determine AA digestibility. In exp. 2, eight castrates (initial BW: 19.11±0.49 kg) were arranged in two 4×4 Latin squares and used in a N balance experiment. Diets consisted of 966.2 g test maize/kg and 33.8 g vitamins, minerals, and salt/kg. In exp.1, apparent ileal digestibility coefficients (CAID) for HO and WX were not different (P>0.05) compared to their respective isogenic maize or YD2. High lysine maize had lower (P<0.05) CAID for isoleucine, leucine, methionine, phenylalanine, threonine, and valine when compared to YD1, its near-isogenic maize, and lower (P<0.05) CAID for isoleucine, leucine, and phenylalanine when compared to YD2. Mean CAID for HO, WX, HL, and YD2 were 0.65±0.05, 0.70±0.05, 0.53±0.05, and 0.60±0.03, respectively. True ileal digestibility coefficients (CTID) for the indispensable AA did not differ when HO and WX maize were compared to their respective isogenic maize, but HL maize had lower (P<0.05) CTID for the majority of indispensable AA except for arginine and histidine than YD1. Mean CTID for HO, WX, HL, and YD2 were 0.78±0.04, 0.84±0.04, 0.67±0.04, and 0.77±0.03, respectively. Nitrogen retained, urinary N, fecal N, N digestibility, and N utilization for HO, WX, and HL were not different (P>0.05) compared to their genetically similar maize. Nitrogen absorbed and DM digestibility were higher (P<0.05) for HO than for IHO. Nitrogen digestibility was similar (P>0.05) for WX compared to YD 2 and greater (P>0.05) for HO and HL compared to YD 2. In conclusion, AA CAID and CTID, were similar for HO and WX maize compared to their isogenic maize, however, AA CAID and CTID for HL maize was lower than its near-isogenic maize. Nitrogen utilization for HO, WX, and HL were similar to that of their respective genetically similar maize.