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Methionine and 2-Hydroxy-4-Methylthiobutanoic Acid Are Partially Converted to Nonabsorbed Compounds during Passage through the Small Intestine and Heat Exposure Does Not Affect Small Intestinal Absorption of Methionine Sources in Broiler Chicks^1,2,3,

Department of Animal and Poultry Science, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 5B5

Broiler chicks were fed diets supplemented with DL-methionine or DL-2-hydroxy-4-methylthiobutanoic acid. At 4 wk of age the chicks were subdivided into thermoneutral (22°C) and heat-exposed (32°C) groups and maintained under these conditions for 48 h. Highly purified ³H-L-methionine (³H-L-Met) and ³H-L-2-hydroxy-4-methyl-thiobutanoic acid (³H-L-HMB) were used to evaluate treatment effects on the small intestinal passage of sources of supplemental methionine and on the transport of methionine sources across purified small intestinal brush border vesicles. ³H-L-Met was efficiently absorbed in the upper regions of the small intestine; however, 2.5–3.5% of dietary ³H from birds fed ³H-L-Met remained unabsorbed in the distal small intestine. Dietary ³H (15%) initially associated with ³H-L-HMB was not absorbed during passage down the length of the gut. The HPLC analysis indicated that only 10% of the radiolabeled material remaining in the terminal ileum eluted at the time expected for HMB. Partial breakdown of HMB to nonabsorbed, nonmethionine products during passage down the small intestine may contribute to the difference in biopotency of the two sources of supplemental dietary methionine. Heat exposure did not affect in vivo small intestinal passage or in vitro transport of ³H-L-Met and ³H-L-HMB across small intestinal brush border membrane vesicles.

KEY WORDS: • methionine • methionine hydroxy analogue • heat exposure • digestibility • chickens

¹ Presented in part at the 83rd Annual Meeting of the Poultry Science Association August 7–12, 1994, Starkville, MS [Maenz, D. D., Engele, C. M. & Classen, H. L. (1994) Transport of methionine (Met) and hydroxymethylthiobutanoic acid (HMB) in the chick intestinal brush border membrane. Poult. Sci. 73: 19 (abs.)].

² Supported by the Degussa Corporation, Ridgefield Park, NJ 07660.

³ The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

⁴ To whom reprint requests should be addressed.

Manuscript received 22 September 1995. Revision accepted 16 January 1996.

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