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Digestion of Hay Protein in Different Segments of the Equine Digestive Tract¹

Texas Agricultural Experiment Stations^,5 College Station 77843

Abstract

Mature ponies fitted with permanent ileal cannulas were used in a 3 x 3 Latin square experiment to quantify prececal, postileal and total tract digestion of hay protein. Coastal Bermuda grass (CB), containing 11.7% crude protein, and two qualities of alfalfa, containing 15.0% (low-protein alfalfa; LA) and 18.1% (high-protein alfalfa; HA) crude protein, were fed in coarsely chopped form at 2% of body weight daily. Total tract apparent digestibility of the N in HA (73.8%) was higher than that in CB (57.0%; P<.05) and was slightly higher than that in LA (66.1%; P<.10). Nitrogen in LA was apparently more digestible than that in CB (P<.05). Apparent prececal digestibilities of N in LA and CB were 1.3% and 9.6%, respectively, and were lower (P<.05), or tended to be lower (P<.10), than the 21.0% observed for HA. In relative terms, an average of 9.4% of the total N digestion occurred in the upper tract when CB and LA were fed, whereas 28.5% of total N digestion occurred in the foregut when HA was fed. There was a slightly higher concentration of total plasma free amino acids (P<.10) at 1 h postfeeding when horses were fed alfalfa. Also, N retention was higher when ponies were fed HA (P<.05) than when LA or CB were fed. Apparent postileal N digestibility was 52.5% for CB, 65.7% for LA and 66.9% for HA. Differences were not significant, and the large intestine appeared to compensate for the inefficiency of N digestion in the upper tract. The large intestine was the major site for apparent digestion of hay N, but the role of the small intestine increased when the high-quality hay was fed. True digestibility estimates indicated that dietary N digestion was virtually complete over the total digestive tract, and true digestibility of hay N was lower in the upper tract (37%) than the lower tract (96%).

¹ Tech. article 21732, Texas Agric. Exp. Sta.

² Current address: Dept. of Anim. Sci., Kansas State Univ.

³ Current address: Dean Lee Res. Sta., Alexandria, LA.

⁴ Dept. of Large Anim. Med. and Surgery.

⁵ Equine Sci. Prog., Dept. of Anim. Sci., Texas A&M Univ.