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Determination of Additivity of Acid-binding Capacity in Diets
Manipulating dietary acid-binding capacity (ABC, mEq/kg) is considered a possible approach to optimize the gastric environment in nursery pigs. The objective of this study was to measure ABC and buffering capacity (BUF, mEq/kg/pH) of feed ingredients, and evaluate their additivity in mixed diets. Additivity is necessary for the values to be used in a formulation matrix. The measured feed ingredients included corn, soybean meal (SBM), spray-dried animal plasma (SDAP), fish meal (FM), dried whey (DW), L-lysine (Lys), DL-methionine (Met), dicalcium phosphate (DCP), and limestone. And the mixed diets were: 1) Corn/SBM; 2) Corn/SBM/DW; 3) Corn/SBM/SDAP; 4) Corn/SBM/FM; 5) Corn/SBM/DW/SDAP/FM; 6) Corn/SBM/DW/SDAP/FM/Lys/Met. Limestone and DCP were included in all diets with varied inclusion rates. Analyzed ABC was measured as the amount of acid required to lower pH to 3.0 for 1 kg of sample; analyzed BUF was calculated as ABC per unit drop in pH. Predicted dietary ABC and BUF were the sum of products of analyzed values of ingredients and their inclusion rates. Results showed that minerals had the highest ABC and BUF (limestone: 12195 and 2282; DCP: 4019 and 1774); the next were protein ingredients (FM: 2107 and 545; SDAP: 1277 and 305; SBM: 1172 and 284), DW (925 and 237), and AA (Lys: 707 and 251; Met: 999 and 343); corn had the lowest capacity to bind acid (234 and 100). Analyzed ABC and BUF of mixed diets were generally lower than predicted values, but predicted and analyzed values of both ABC (P = 0.008, R2 = 0.83) and BUF (P = 0.008, R2 = 0.83) were highly correlated. In this study, the ABC or BUF values of ingredients lacked strict additivity in mixed diets. However, because the ratios of analyzed to predicted values ranged 92-97% and 89-93% for ABC and BUF across all diets, respectively; the predicted values can be used to estimate ABC and BUF.
Table. Difference between predicted and analyzed values of ABC and BUF of diets
Item |
ABC, mEq/kg |
|
BUF, mEq/kg/pH |
||||||
Predicted |
Analyzed |
Ratio |
P value |
Predicted |
Analyzed |
Ratio |
P value |
||
Diet 1 |
843 |
795 |
94% |
0.11 |
227 |
209 |
92% |
0.10 |
|
Diet 2 |
905 |
838 |
93% |
0.01 |
236 |
218 |
92% |
0.02 |
|
Diet 3 |
793 |
730 |
92% |
0.08 |
217 |
193 |
89% |
0.03 |
|
Diet 4 |
808 |
768 |
95% |
0.10 |
219 |
201 |
92% |
0.03 |
|
Diet 5 |
824 |
772 |
94% |
0.04 |
219 |
199 |
91% |
0.01 |
|
Diet 6 |
796 |
773 |
97% |
0.34 |
|
215 |
201 |
93% |
0.09 |
Keywords: acid binding capacity, buffering capacity, nursery diets