Comparison of two in vitro methods progressed in a computer-controlled simulated digestion system to determine amino acid digestibility of feed ingredients for yellow-feathered roosters

This experiment compared amino acid (AA) digestibility assessed by 2 in vitro methods using a computer-controlled simulated digestion system and in vivo assay for corn, soybean meal, casein, corn gluten meal, cottonseed meal, rapeseed meal and a corn-soybean meal diet. In vitro method 1 simulated gizzard digestion at pH 2.0, followed by small intestinal digestion, and the subsequent clearance of the digested product from dialysis tubing. In vitro method 2 was similar to the first method, except that pH in gizzard digestion was 3.5 and there was an enzymatic inactivation stage before digested product clearance. Each in vitro method included 5 replicates per treatment, with 1 digestion tube per replicate. Cecectomized Chinese yellow-feathered roosters (average body weight of 2.73 kg) were assigned to 1 of the following treatments: corn, soybean meal, or a corn-soybean meal diet (n = 6 replicates of 3 roosters per treatment); or casein, corn gluten meal, cottonseed meal, or rapeseed meal (n = 5 replicates of 3 roosters per treatment) in a completely randomized design to assess digestibility of AA. The relative deviation was within 5% comparing methods 1, 2 and in vivo method for 87.5% and 92.0% of all AA digestibility measured of 7 samples, respectively. Significant linear relationships were observed between in vitro methods 1 and 2 for the digestibility of 14 AAs (except for Cys) and total amino acid (TAA) (r ≥ 0.778; P < 0.05). Significant linear relationships were found between in vitro method 1 and in vivo results for 9 AAs (except for His, Ile, Asp, Cys, Glu and Ser) and TAA (r ≥ 0.866; P < 0.05). Similarly, significant linear relationships between in vitro method 2 and in vivo findings were observed for 11 AAs (except for His, Lys, Cys and Glu) and TAA (r ≥ 0.776; P < 0.05). The linear regression of in vivo assay on in vitro method 1 or 2 overlapped with Y = X for 7 AA and TAA or 10 AA and TAA, respectively. Our findings suggest in vitro method 2 is superior to method 1 for estimating AA digestibility of yellow-feathered roosters, this indicates that gizzard pH or inactivation of enzymes modulates the effectiveness of in vitro digestibility assays.

Variation in lysine, threonine, and tryptophan availability in meat and bone meal as estimated by the slope-ratio growth assay technique in growing rats

Meat and bone meal (MBM) is an important protein source used in animal feeds. However, as the composition and availability of amino acids (AAs) in MBM fluctuate markedly, it is important to verify the magnitude of these parameters in different MBMs. In this study, the AA compositions of 19 MBMs were analyzed to confirm variations in lysine (Lys), threonine (Thr), and tryptophan (Trp), then which were compared with those of soybean meal (SBM) and fish meal (FM). Instability in Lys, Thr, and Trp availabilities in six MBMs were also considered after estimation using the slope-ratio growth assay technique in rats. Variations in AA composition were evaluated using the coefficient of variance (CV: Standard deviation/Mean). CVs for Lys, Thr, and Trp content were 9.40, 11.83, and 18.12 in MBM, 2.71, 2.48, and 3.19 in SBM, and 10.09, 10.44, and 13.47 in FM. Furthermore, means and SDs for Lys, Thr, and Trp availabilities in MBM were 53.3 ± 10.4% (CV: 19.5), 65.9 ± 17.6% (CV: 26.6), and 83.2 ± 11.2% (CV: 13.5), respectively. These results provide the first evidence that variations in MBM AA compositions were 3.5 to 5.7 times higher than those in SBM, but similar to FM, and that the large variation in availability substantially existed.

Amino acid digestibility in six sources of meat and bone meal, blood meal, and soybean meal fed to growing pigs

Standardized ileal digestibility (SID) of amino acids (AAs) by growing pigs was determined in blood meal and six sources of meat and bone meal (MBM). Eighteen ileal-cannulated barrows (initial body weight: 69.3 ± 4.4 kg) were randomly allotted to a replicated 4 × 9 incomplete Latin square design with four periods and nine diets, giving eight replications per diet. One diet included 33% soybean meal (SBM) as the sole source of AA. Seven diets contained 9% blood meal or 9% of one of the six sources of MBM and 22% SBM as the only AA containing ingredients. The last diet was a nitrogen (N) free diet. Results indicated that the SID of all AAs were different (P < 0.05) among the six sources of MBM, but the SID of lysine (Lys) could not be predicted from the ratio between Lys and crude protein. For some, but not all AAs, the average SID in MBM was greater (P < 0.05) than in blood meal, but for most AAs the SID in MBM was less (P < 0.05) than in SBM. It is concluded that, as is the case for most other co-products, differences in concentration and SID of AAs among sources of MBM exist.