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Validating dietary approach to determine the Trp:Lys ratio for pigs
Three experiments were conducted to validate a dietary approach to determine the optimal standardized ileal digestible (SID) Trp:Lys ratio for pigs. Corn-soybean meal-based diets with 30% DDGS were used with different SID Trp:Lys ratios (14.5% vs. 20%), CP (3 percentage points difference), and SID Lys levels (0.05% below requirement at the end of the phase vs. 0.01% above requirement at the beginning of the phase). Lysine requirements were estimated using NRC (2012) model. All experiments had 11 pens/treatment, were 21 d in duration, and used 1,183 to 1,232 gilts (PIC 337 × 1050) with 24 to 28 pigs/pen. Initial BW for the 3 experiments were 22.8, 57.7, and 87.4 kg, respectively. Dietary treatments in all experiments were: (1) High CP, High Lys, and High Trp:Lys (HHH); (2) Low CP, High Lys, and High Trp:Lys (LHH); (3) Low CP, Low Lys, and High Trp:Lys (LLH); and (4) Low CP, Low Lys, and Low Trp:Lys (LLL). Data were analyzed using Proc Mixed with pen as the experimental unit. Lowering CP (HHH vs LHH) did not influence performance in any experiment, except G:F were greater in HHH compared to LHH in Exp. 1 and 3. Decreasing lysine (LHH vs LLH) reduced ADG and G:F in Exp. 1, but did not significantly reduce ADG or G:F in Exp. 2 or 3. Decreasing Trp:Lys ratio (LLH vs LLL) decreased ADG and G:F in all experiments. It appears that Lys was not as limiting as expected in Exp. 2 and 3, but pig performance was improved when Trp:Lys was increase from 14.5 to 20%. In conclusion, a low CP diet formulated 0.05% below the SID Lys requirement at the end of the dietary phase appears to be valid to ensure pigs are below their Lys requirement to test the Trp:Lys ratio.
Diet |
HHH |
LHH |
LLH |
LLL |
SEM |
Exp. 1 |
|
|
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CP, % |
23.2 |
20.2 |
17.6 |
17.6 |
-- |
SID Lys, % |
1.09 |
1.09 |
0.92 |
0.92 |
-- |
ADG, g |
713c |
727c |
654b |
492a |
13.8 |
G:F |
0.617d |
0.586c |
0.521b |
0.487a |
0.010 |
Exp. 2 |
|
|
|||
CP, % |
20.7 |
17.6 |
16.2 |
16.2 |
-- |
SID Lys, % |
0.92 |
0.92 |
0.80 |
0.80 |
-- |
ADG, g |
760b |
779b |
754b |
661a |
17.1 |
G:F |
0.415b |
0.405b |
0.391b |
0.363a |
0.010 |
Exp. 3 |
|
|
|||
CP, % |
18.9 |
16.0 |
14.6 |
14.6 |
-- |
SID Lys, % |
0.79 |
0.79 |
0.65 |
0.65 |
-- |
ADG, g |
1033c |
986bc |
965b |
868a |
18.3 |
G:F |
0.386a |
0.370b |
0.360b |
0.339c |
0.004 |
a,b,c,d P<0.05. |
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Keywords: amino acids, pigs, tryptophan