Digestion & Absorption of Protein along the Intestinal Tract of Chicks Fed Raw and Heated Soybean Meal

Presented By Ahmed M. Al-Zahrani – PhD student (reference attached) Animal Science Department Protein Metabolism Advisor Prof. Dr. Ahmed M. El-Waziry Jun 2010

Contents Introduction Chicken Digestive System Methods Results & Discussion Conclusions

Introduction

The goal of this experiment is to evaluate the net absorption and digestion of Protein in chicks fed (HS) & (RS) using 91 Y as a reference substance. To eliminate its long-term effects, RS was fed for 4 days to 15-day –old chicks.

Diet with RS: Inhibit Protein digestion in the intestine (reflected by depressed proteolytic activity) - duodenum not included Pancreatic hypertrophy and an increased proenzyme production also occur Measurement & Evaluation: By employing a reference substance the digestion and absorption can be quantitatively evaluated at different sites along the intestinal tract/segment.

Chicken Digestive System

فول صويا

Materials & Methods

Animals and diets  Day-old New Hampshire X Leghorn male chicks were housed in a four-deck battery brooder (155 g weigh).  They were fed a commercial chick ration containing 22% Protein for 15 days.  The Chicks were then divided into four groups and fed the experimental diets for 4 days.

Experimental Protein absorption and digestion evaluated by the use of yttrium-91. The isotope was uniformly mixed into the diets at a concentration of 100 μCi/kg At the end of the 4-day chicks were killed by an overdose of Nembutal. The intestines were immediately removed and separated into six segments: duodenum, upper and lower jejunum, upper and lower ileum, and colon.

intestinal contents from the segments obtained from two, three or four chicks were pooled. The pooled samples were homogenized and brought to volume with water. Aliquots of the homogenates were assayed for dry matter (105°), yttrium-91, total and ultrafilterable nitrogen.

 The percentage net nitrogen absorption and digestion were calculated using the following equations:  % Net absorption =100 [1-(Nt/Y)s / (Nt/Y)f]  % Net digestion =100 {1 - [ (Nt - Nu)/Y]s / (Nt/Y)f}  Where Nt =total nitrogen Nu = ultrafilterable nitrogen Nt - Nu = undigested nitrogen Y = yttrium-91.  The subindices S and F denote "segment" and "feed”, respectively.

Determination of proteolytic activity Proteolytic activity was markedly inhibited as a result of RS feeding On day 4 of RS feeding there was a slight increase in the proteolytic activity in the homogenate obtained from group 3 (25%-RS)

Results & Discussion

The inhibition of Protein digestion in the intestine of chicks fed raw soybean meal is reflected by depressed proteolytic activity. In response to the presence of RS in the diet pancreatic hypertrophy and an increased proenzyme production also occur

In the duodenum of the RS–fed chicks: Extensive nitrogen secretion proportional to the RS levels in the diets occurred (It is reabsorbed in the upper jejunum). Net digestion values were also proportional to the RS levels in the diets. When the duodenal N-secretion is taken into account it is concluded that as in chicks fed HS most of the food Protein was digested in the duodenum of the RS–fed chicks.

The average gains during the 4-day experimental period were significantly lower in chicks fed the diets containing RS than in those fed only HS. The difference in feed efficiency indicates that this weight gain difference was not due to a decreased food intake.

Nt/Y ratios: Increase in the Nt/Y ratio in the segments above diet (clear evidence of nitrogen secretion) The Nt/Y ratio in the duodenal contents of chicks fed RS always exceeded the ratio in the diet In the HS-fed chicks this ratio was slightly lower than that of the diet The Nt/Y ratios in the remaining segments except in the upper jejunum, were significantly (p < 0.05) higher for the RS-than the HS-fed chicks, but lower than the Nt/Y ratio in the diet (Nt-Nu)/Y: The trend of nitrogen secretion is more pronounced when the undigested nitrogen to yttrium-91 ratios are compared

The 20% difference in net digestion between (HS & RS) is result of inhibition of proteolysis in segments beyond the duodenum. The jejunum is the main site of absorption in (HS & RS)-fed chicks. The absorption process in this segment is enhanced and not impaired by RS. The 20% difference in protein absorption between (HS & RS) groups is probably the result of a corresponding inhibition in digestion beyond the duodenum.

Digestion in the duodenum & absorption in the jejunum was confirmed. About 20% additional digestion occurred in the remaining segments Digestion in the duodenum ↓ with ↑ levels of RS. This was result of ↑ nitrogen secretion (fig. 2a) Due to ↑ nitrogen secretion into this segment (fig. 2a), the net digestion of food protein cannot be evaluated The 70 % net digestion observed in the upper jejunum of all RS groups following the reabsorption of the secreted nitrogen, probably had taken place in the duodenum.

No additional digestion was found beyond the Jejunum. The 20% difference in net digestion between the HS and RS groups prevailed down to the lower ileum. The net absorption in the duodenum decreased in direct proportion to the RS levels in the diet (fig. 3a). This decrease results from the increased secretion of nitrogen which was reabsorbed in the upper jejunum.

In HS-fed chicks a cumulative digestion of 90% was attained: 70% in the duodenum and an additional 20% in the remaining segments.

The values of water to yttrium ratio indicate an ↑ water secretion in the duodenum of chicks fed any of the three levels of RS as compared with the HS. These quantities of water were almost completely reabsorbed in the upper Jejunum with a slight, but not statistically significant difference prevailing between the RS and HS groups. The remainder of the secreted water is gradually absorbed along the intestinal tract, and in the upper ileum no differences between the RS and HS groups exist.

Conclusion

HS activate the proteolytic enzymes/activity along the SI which strengthen the digestion and absorption. Nitrogen and water secretion were high in RS-chicks comparing to HS-chicks along the segments of SI. RS contain trypsin inhibitors which cause hypertrophic pancreas and minimize digestibility. Efficiency was higher for HS fed-chicks in gain and feed conversion comparing to RS fed-chicks.

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