Effects of Supplementing Synthetic Amino Acids into Low Crude Protein Diets fed to Pigs from 1.5 to 5.5 kg.

Abstract

Liquid diets provide a useful tool for producers with low birth weight pigs, as these pigs are at a disadvantage compared to larger littermates. There is limited use of milk replacers on commercial farms due to the high cost of protein sources. A way to potentially reduce the cost of liquid diets is to replace protein sources with synthetic amino acids (AA).

Experiment 1 was designed to determine the amount of synthetic lysine (SL) that could replace lysine from protein and maintain performance similar to pigs fed a diet containing no SL. Pigs (1.62±0.20 kg) were randomly allotted to diets which replaced 0 to 40% of lysine from protein with SL, while maintaining similar GE and total lysine. Diets were fed on a restricted basis (n=4⁄diet) in order to reduce intake differences. An additional group was fed the 0% SL replacement diet ad libitum (AL, n=5) to determine intake level. Intake for restricted pigs was restricted to 80% of AL and adjusted on a daily basis. Pigs fed AL had greater (P < 0.01) ADG, ADFI, G:F, water, CP, fat, and ash accretion than restricted fed pigs. Gain, G:F, water, CP, and ash accretion decreased (P < 0.05) linearly from 286 g⁄d, 1.09, 180.6 g⁄d, 38.6 g⁄d, and 5.4 g⁄d for pigs fed the 0% replacement diet to 229 g⁄d, 0.86, 134.2 g⁄d, 26.3 g⁄d, and 3.6 g⁄d for pigs fed the 40% replacement diet, respectively. Crude protein accretion also showed a quadratic effect (P < 0.05) as the decrease occurred more rapidly at greater SL replacement. Fat accretion increased (P < 0.05) linearly from 16.4 g⁄d for pigs fed the 0% replacement diet to 28.4 g⁄d for pigs fed the 40% replacement diet. Intake and PUN concentration did not differ (P > 0.05) among restricted fed pigs. Replacement of lysine from protein with SL did not produce performance similar to pigs on the control diet. Based on quadratic data for ADG and CP accretion, the next AA could become limiting between 15 and 19% SL replacement.

Experiment 2 was designed to determine the order of limiting AA beyond lysine (LYS). Pigs (1.71±0.30 kg Rep. 1, 1.62±0.11 kg Rep. 2) were allotted randomly to seven diets for a deletion assay using a positive control diet (PC) with AA concentrations and ratios to LYS at or above NRC recommendations, a negative control diet (NC) that reduced AA concentrations and ratios to LYS to 60% of ratios in the PC diet, a supplemented negative control diet (Supp. NC) with AA supplemented to provide concentrations and ratios to LYS similar to those found in the PC diet, and deletion diets which removed threonine (-THR), tryptophan (-TRP), sulfur amino acids (-SAA), or phenylalanine (-PHE) from Supp. NC. All diets contained 4.2 Mcal GE and 20.6 g LYS⁄kg DM, and were fed ad libitum (n=8⁄diet). Blood samples were taken to measure PUN. Gain for pigs fed PC (346 g⁄d), NC (269 g⁄d), and Supp. NC (315 g⁄d) diets differed (P < 0.05). Gain of pigs fed deletion diets was similar. The SAA deletion diet produced less gain (291 g⁄d, P < 0.05) than the Supp. NC diet. Intake was similar in pigs fed the PC and NC diets, and greater (P < 0.05) than for pigs on other diets. Efficiency decreased for pigs fed the NC diet (P < 0.05) compared to other diets. Pigs fed the SAA deletion diet had the greatest PUN (6.96 mM, P < 0.05). Based on increased PUN concentration and decreased gain relative to the Supp. NC diet, it is likely that the SAA were next limiting.