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Keywords

di-ammonium phosphate, non-protein nitrogen, nursery pig, SID Lys:CP

Abstract

A total of 981 mixed-sex pigs ([Fast LW × PIC L02] × PIC 800; initially 22.8 ± 0.42 lb) were used in a 21-d study to determine if nitrogen, derived from non-protein nitrogen or amino nitrogen, is the limiting factor to maintain feed efficiency when feeding low protein, amino acid fortified diets. Pens of pigs were randomly allotted to one of five dietary treatments in a randomized complete block design with BW as a blocking factor. There were 19 to 20 pigs per pen and 10 pens per treatment. The experimental diets were corn-soybean meal-based and were fed when pigs reached an approximate BW of 23 lb, considered d 0 of the study. The five treatments consisted of: 1) low level of feed-grade AAs with a SID Lys:CP ratio of 6.0:1; 2) moderate level of feed-grade AAs with a SID Lys:CP ratio of 6.5:1; 3) high level of feed-grade AAs with a SID Lys:CP ratio of 7.0:1; 4) diet 3 with di-ammonium phosphate (DAP) added to achieve a SID Lys:calculated CP ratio of 6.5:1; 5) diet 3 with glycine added to achieve a SID Lys:calculated CP ratio of 6.5:1. All diets contained 0.4% titanium dioxide for determination of apparent total tract digestibility (ATTD) of dry matter (DM) and crude protein (CP). Treatment diets were fed for 21 days. Feces were collected on d 21 from three pigs per pen to determine fecal DM. Overall (d 0 to 21), ADG was not influenced by treatment. Feed efficiency worsened (linear, P = 0.002; quadratic, P = 0.054) as the SID Lys:CP ratio was increased above 6.5% with additional feed-grade AAs. Adding DAP or glycine to the high feed-grade AA diet improved (P ≤ 0.003) feed efficiency compared to pigs fed the high feed-grade AA diet because of a reduction (P = 0.007) or numerical reduction (P = 0.109), respectively, in ADFI. There was a decrease (linear, P < 0.001) in blood urea nitrogen (BUN) as feed-grade AAs increased. Adding additional nitrogen to the high feed-grade AA diet increased (DAP; P = 0.038) or tended to increase (glycine, P = 0.091) BUN. There was a tendency (quadratic, P = 0.051) in fecal DM with pigs fed the moderate feed-grade AA diet having the lowest fecal DM. Pigs fed the diet containing DAP had increased (P = 0.005) fecal DM compared with pigs fed the high feed-grade AA diet. There was a tendency for an increase (P = 0.060) in the ATTD of DM for pigs fed the DAP diet compared with the pigs fed the high feed-grade AA diet. The ATTD of CP decreased (linear, P = 0.048) as the SID Lys:CP ratio increased. Pigs fed the diets containing either DAP or glycine had increased (P ≤ 0.026) CP digestibility compared with pigs fed the high feed-grade AA diet. These data suggest that diets for 25 to 50 lb pigs should be formulated to a SID Lys:CP ratio of 6.5 or lower and that adding a non-protein nitrogen source or non-essential AA to diets formulated above this ratio can improve feed efficiency and CP digestibility.

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