An experiment was conducted to estimate by simple linear regression the levels of endogenous amino acids in digesta collected from the distal ileum in pigs. Six barrows, average initial BW 35 kg, were fitted with a simple T-cannula at the distal ileum and fed six diets according to a 6 x 6 Latin square design. Six cornstarch-based diets containing six levels of CP from soybean meal (4, 8, 12, 16, 20, and 24% CP, respectively) were formulated. Chromic oxide (.4%) was included as the digestibility marker. Each experimental period consisted of 8 d. Ileal digesta were collected, at 2-h intervals, for a total of 24 h during d 7 and 8. There were linear relationships (P < .001) between dietary contents of apparent ileal digestible and total amino acids, irrespective of the ranges in graded dietary levels of amino acids. Determined with the regression technique, the endogenous levels of the indispensable amino acids (grams/kilogram of DMI) were as follows: arginine, .64; histidine, .23; isoleucine, .46; leucine, .69; lysine, .47; methionine, .13; phenylalanine, .31; threonine, .69; and valine, .54. Differences in the ranges of graded dietary levels of amino acids resulted in large differences in the estimated amounts of endogenous amino acids in ileal digesta. Furthermore, it seems that the levels of endogenous amino acids, as grams/kilogram of DMI, were constant at different dietary levels of amino acids, whereas the contributions of endogenous amino acids, as percentages of their dietary contents, decreased curvilinearly with increasing dietary contents. Therefore, apparent ileal digestibilities of amino acids were quadratically related to their dietary contents until plateau digestibilities were reached, whereas the true ileal digestibilities of amino acids were independent of their respective dietary contents. Furthermore, true ileal amino acid digestibilities should be determined from their corresponding plateau apparent ileal digestibilities. In conclusion, the levels of endogenous amino acids in ileal digesta can be determined reliably from the linear relationships between dietary contents of apparent ileal digestible and total amino acids. An important methodological consideration in the determination of endogenous amino acids by regression analysis is to design an appropriate range of graded dietary levels of amino acids.

Supplementation of microbial phytase usually improves the digestibility and utilization of phosphorus in feedstuffs of plant origin. The effect of phytase supplementation on the digestibilities of AA also has been examined, but the results have been inconsistent. This study was carried out to determine the effect of phytase (Natuphos) supplementation, at a rate of 2,000 phytase units/kg, to two basal diets on the apparent ileal digestibilities (AID) of GE, CP, and AA, and on the apparent total-tract digestibilities (ATTD) of CP and GE. The basal diets contained 18% CP and were formulated (as-fed basis) to contain either a low (0.22%) or high content (0.48%) of phytate P. The high-phytate diet contained 20% rice bran, which is a rich source of phytate and has low intrinsic phytase activity. Eight barrows (average initial BW = 40.6 kg), fitted with a simple T-cannula at the distal ileum, were fed the four diets according to a replicated 4 x 4 Latin square design. The pigs were fed twice daily at 0800 and 2000, equal amounts each meal, at a rate of 2.4 times the daily maintenance requirement for ME. Each experimental period comprised 14 d. Ileal digesta were collected from 0800 to 2000 on d 12, 13, and 14. Feces were collected from 0800 on d 8 until 0800 on d 12. Chromic oxide was used as the digestibility marker. The AID of GE, CP, and AA and the ATTD of CP and GE were less in the high- than in the low-phytate diet (P < 0.01). With the exception of glutamic acid, phytase supplementation did not affect (P > 0.10) the AID of CP and AA. There was no effect (P > 0.05) of phytase on the ATTD of CP and GE. These results show that if a response occurs to phytase supplementation, it is independent of the dietary phytate content.

Five Yorkshire x Lacombe barrows (45 kg initial wt) fitted with duodenal cannulas approximately 10 cm from the pyloric sphincter were used to determine the influence of the pH of the predigestion solution (pH 1.0, 1.5, 2.0 or 2.5), pepsin activity (189 vs 377 IU/liter) and duration of predigestion (0, 1.5, 2.5 or 4.0 h) on the apparent digestibility of the protein in soybean meal (SBM), meal and bone meal (MBM) or canola meal (CM) determined with the Mobile Nylon Bag Technique (MNBT). An additional six barrows were used to determine protein digestibility by conventional methods. Protein digestibilities determined using conventional digestibility techniques were 93.1 +/- .7, 79.1 +/- 1.8 and 79.3 +/- 1.4% for the SBM, MBM and CM diets, respectively. Protein digestibilities determined with the MNBT were highest at pH 2.0 for all three protein sources. Increasing pepsin activity from 189 to 377 IU/liter resulted in a slight increase in the digestibility of SBM and CM, but not of MBM. The absence of predigestion (0 h) resulted in a dramatic reduction in protein digestibility; predigestion times of 1.5 or 2.5 h usually resulted in lower protein digestibilities than did a predigestion time of 4.0 h. The closest agreement between results obtained by the MNBT and conventional digestibility studies occurred with a pH of 2.0, a predigestion time of 4.0 h and a pepsin activity of 377 IU/liter.

Studies were carried out with six growing barrows fitted with a simple T-cannula 5 to 10 cm anterior to the ileo-cecal sphincter. In Exp. 1, the digestibility of biotin was determined in three cornstarch-based diets formulated to contain 16% CP by supplementation with soybean meal (SBM), meat and bone meal (MBM) and canola meal (CM). In Exp. 2 the digestibility of biotin was determined in three diets that contained 96.8% barley, corn or wheat. Experiments 1 and 2 were conducted according to a replicated 3 X 3 latin square design. In Exp. 3 pigs were fed a cornstarch-based diet supplemented with 12% vitamin-free casein to determine the amount of endogenous biotin. In Exp. 4 the digestibility of supplemental biotin was determined. There was a small amount of endogenous biotin in ileal digesta, 11 micrograms/kg DMI. Digestibilities of biotin determined at the distal ileum (apparent digestibilities corrected for endogenous biotin) were 55.4, 2.7 and 3.9% in SBM, MBM and CM, respectively, and 4.8, 4.0 and 21.6% in barley, corn and wheat, respectively. The digestibility of supplemental biotin was 93.5%. There was a large increase in the level of biotin between digesta collected from the distal ileum and in feces, ranging from 138 to 324 micrograms/kg DMI. With the exception of the CM diet, this increase exceeded dietary biotin intake. Biotin in many feedstuffs was not available in the small intestine.