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Effects of low dietary inclusion levels of soybean meal and non-essential amino acid supplementation on the growth performance of late-finishing pigs
There has been limited research to establish if non-essential amino acids (NEAA) become limiting to growth performance in late-finishing pigs fed diets low in crude protein. The objectives of this study were to define the minimum dietary crude protein level in corn-soybean meal based diets to maintain growth performance and establish if NEAA become limiting in low crude protein diets for late-finishing pigs. Individually penned barrows (n = 144; initial BW 89.4 ± 5.16 kg) were randomly allotted to 8 dietary treatments in a RCBD with 18 replicates. Diets for Treatments 1 to 5 were formulated by reducing soybean meal inclusion levels (18.0, 14.0, 10.0, 7.0 and 3.0%), which resulted in dietary crude protein levels of 13.0, 12.0, 10.7, 9.5, and 8.4%, respectively. Diets were formulated to the same ME (3.3 Mcal/kg) and standard ileal digestible lysine (0.60%) levels and met or exceeded NRC (1998) recommendations for other nutrients. Levels of other essential AA were maintained constant across diets by the addition of crystalline AA sources. For Treatments 6, 7, and 8 the diets contained the same crude protein levels as Trt. 1 by the addition of NEAA (50:50% mixture of glycine and glutamic acid) to Trt. 3, Trt. 4, and Trt. 5, respectively. Pigs had ad libitum access to experimental diets for a 4-wk period. Reducing crude protein levels resulted in reduced (quadratic, P < 0.05) ADG (1.147, 1.143, 1.156 and 1.118, and 0.999 kg, respectively), and reduced (quadratic, P < 0.05) G:F (0.352, 0.342, 0.350, 0.331, and 0.308, respectively). There was no effect (P > 0.05) of reducing dietary crude protein level on ADFI. Broken-line regression analysis suggested that the minimum crude protein inclusion level for ADG, and G:F was 9.76 and 10.32%, respectively. There were no improvements (P > 0.05) in growth performance with NEAA supplementation, regardless of dietary crude protein level. These results suggest that for late-finishing pigs fed corn-soybean meal based diets the minimum crude protein to maintain growth performance was between 9.76 and 10.32% and that NEAA were not limiting in the low crude protein diets evaluated.
Keywords:
Low crude protein, non-essential amino acids, finishing pigs, growth.