Amino acid rather than total protein requirement is the primary consideration of nutritionists in formulating poultry diets. Recently, it has been suggested that if a ration is formulated on the basis of amino acid (AA) bioavailability instead of AA concentration, it becomes more beneficial for productive performance of birds. For this purpose information on bioavailable contents of AAs in feedstuffs are required. However, at present no such data appears to be available on the feed ingredients of Indian origin. It is more important and pertinent to generate data on bioavailabilities of lysine, methionine and tryptophan since these three amino acids are among the essential and limiting ones in poultry diets. Therefore, studies have been undertaken in order to determine the digestibility and bioavailability of these three AAs in the different samples of commonly used two protein rich feedstuffs viz., SBM and FM in poultry diets.
Samples of soybean (SBM) and fish meal (FM) were collected from across the country and analyzed for proximate principles. Ten samples from each feed ingredient were selected on the basis of their variability in respect of chemical constituents. These samples were analyzed further for the content of lysine, methionine, tryptophan and FDNB-reactive lysine. Bioassays were conducted with intact and caecectomized roosters for the estimation of digestibility and availability of lysine, methionine and tryptophan as well as apparent (AME) and true metabolizable energy (TME) content in either feedstuff.
The chemical compositions including lysine, methionine and tryptophan concentrations in SBM and FM varied among the samples of both feedstuffs (Tables 3, 4, 5 and 6) but the magnitude of variation was higher in FM. Biological experiments indicated that lysine was equally digestible (82%) in SBM and FM. However, digestibility of methionine (90%) and tryptophan (87%) in SBM was higher than in (83 and 74%). Bioavailability recorded in SBM for lysine, methionine and tryptophan (85, 93 and 90%) was found to be higher than in FM (83, 83 and 76%). Bioavailability variation in either feedstuff followed a similar trend to that of digestibility. Caecectomy had significant effect only on dry matter digestibility of both feed ingredients but did not exert any influence on the digestibility and bioavailability of nitrogen, three amino acids as well as AME and TME. SBM had higher nitrogen digestibility (77%) and bioavailability (89%) than that of FM (74 and 88%). AME and TME concentrations of SBM (2.50 and 3.20 kcal/g) were also observed to be higher than that of FM (2.20 and 2.70 kcal/g). The energy metabolizability was highly variable in FM (CV = 25%) as compared to SBM (CV = 2%). FDNB-reactive lysine had high correlation with crude protein, total digestible and bioavailable lysine in SBM or FM. This study also resulted in development of promising prediction equations for estimating the three amino acids content and their bio-availabilities in SBM and FM.
Table 3. Prediction equations for the estimation of amino acid contents in soybean and fishmeals
Soybean meal | ||
Lysine (%) |
= |
-1.19 – 0.054 x moisture (%) + 0.059 x CP (%) + 0.60 x EE (%) + 0.026 x CF (%) + 0.055 x (R2 = 0.87) |
Methionine (%) |
= |
4.01 – 0.023 x moisture (%) – 0.034 x CP (%) + 0.015 x EE (%) – 0.068 x TA (%) – 0.038 x NFE (R2 = 0.69) |
Tryptophan (%) |
= |
2.828 – 0.026 x moisture (%) – 0.105 x EE (%) – 0.066 x CF (%) – 0.097 x TA (%) – 0.028 x (R2 = 0.69) |
Fish meal | ||
Lysine (%) |
= |
-54.91 + 0.54 x moisture (%) + 0.54 x CP (%) + 1.22 x EE (%) + 1.54 x CF (%) + 0.58 x TA (%) (R2 = 0.94) |
Methionine (%) |
= |
-17.89 + 0.24 x moisture (%) + 0.19 x CP (%) + 0.29 x EE (%) + 0.57 x CF (%) + 0.17 x TA (%) (R2 = 0.91) |
Tryptophan (%) |
= |
-5.92 + 0.047 x moisture (%) + 0.064 x CP (%) + 0.109 x EE (%) + 0.14 x CF (%) + 0.062 x TA (R2 = 0.86) |
Table 4. Regression equations relating the bioavailability of amino acid to the nitrogen bioavailability
Fish meal | ||
Lysine BA (%) |
= |
-39.99 + 1.39 x (R2 = 0.85) |
Methionine BA (%) |
= |
-50.52 + 1.52 x (R2 = 0.81) |
Tryptophan BA (%) |
= |
-83.60 + 1.81 x (R2 = 0.68) |
Soybean meal | ||
Lysine BA (%) |
= |
-1.48 + 0.98 x (R2 = 0.79) |
Methionine BA (%) |
= |
61.30 + 0.36 x (R2 = 0.46) |
Tryptophan BA (%) |
= |
59.29 + 0.35 x (R2 = 0.48) |
Table 5. Total lysine, methionine and tryptophan content of soybean meals
Sample |
Total lysine |
Methionine |
Tryptophan |
FDNV reactive lysine (%) |
S1 |
3.57±0.13a |
0.847±0.010a |
0.938±0.008a |
3.22±0.04a |
S2 |
2.70±1.00c |
0.628±0.010e |
0.792±0.005b |
2.24±0.04d |
S3 |
3.12±0.04b |
0.766±0.006c |
0.760±0.008cd |
2.74±0.04b |
S4 |
2.43±0.08de |
0.573±0.004f |
0.583±0.008h |
1.87±0.04f |
S5 |
3.11±0.05b |
0.724±0.004d |
0.729±0.010ef |
2.64±0.04b |
S6 |
3.02±0.08b |
0.750±0.007c |
0.750±0.011cde |
2.65±0.58b |
S7 |
2.86±0.09bc |
0.728±0.009d |
0.696±0.08g |
2.47±0.03c |
S8 |
2.73±0.09c |
0.605±0.008e |
0.746±0.008de |
2.30±0.04d |
S9 |
2.30±0.06e |
0.798±0.006b |
0.771±0.008bc |
1.56±0.02g |
S10 |
2.64±0.09cd |
0.726±0.008d |
0.708±0.008fg |
2.06±0.02e |
Overall |
2.85±0.12 (13.07) |
0.715±0.03 (12.20) |
0.747±0.03 (11.85) |
2.38±0.15 (20.07) |
Table 6. Total lysine, methionine and tryptophan content of fishmeals
Sample |
Total lysine |
Methionine |
Tryptophan |
FDNB reactive lysine (%) |
F1 |
5.18±0.04ab |
2.02±0.08ab |
0.612±0.004ab |
4.65±0.08a |
F2 |
5.43±0.10a |
2.18±0.03a |
0.783±0.006a |
4.90±0.09a |
F3 |
2.50±0.19g |
1.20±0.05e |
0.308±0.006c |
1.50±0.12f |
F4 |
4.59±0.07d |
1.65±0.09c |
0.450±0.007bc |
4.12±0.04c |
F5 |
4.09±0.12e |
1.61±0.10c |
0.448±0.005bc |
3.69±0.05d |
F6 |
4.92±0.07bc |
1.98±0.12ab |
0.617±0.005ab |
4.43±0.04b |
F7 |
4.83±0.05cd |
1.82±0.09bc |
0.558±0.005b |
4.30±0.05bc |
F8 |
4.68±0.08cd |
1.60±0.07cd |
0.517±0.004b |
4.13±0.04c |
F9 |
4.14±0.04c |
1.38±0.06d |
0.452±0.006bc |
3.62±0.04d |
F10 |
3.00±0.06f |
1.24±0.06e |
0.317±0.06c |
2.08±0.02e |
Overall |
4.34±0.30 (21.65) |
1.67±0.11 (19.98) |
0.506±0.05 (28.51) |
3.74±0.35 (29.61) |
