| Abstract: | Four horses fitted with permanent posterior ileal cannulas were assigned diets in a 4x4 Latin square experiment to measure nitrogen digestion in different segments of the digestive tract. Using a commercial protein supplement, rations were formulated to contain 14% crude protein and to meet all other N.R.C. nutrient requirements for horses at light work. Rations varied only in the source of grain or processing treatment, containing either crimped oats (CO), micronized oats (MO), crimped milo (CM) or micronized milo (MM). Horses were maintained in box stalls with ad libitum access to water and were exercised daily on a mechanical walker. The concentrate was fed in a 50:50 ratio with coastal bermudagrass hay at 2% of the horses' body weight daily. Chromic oxide was fed at a rate of 109 per feeding in the concentrate for 10 days prior to sampling. Ileal samples were collected immediately prior to the morning feeding and at 30 minute intervals for 6 hours. Fecal grab samples were taken at 2-hr intervals after feeding. Feed, ileal and fecal samples were analyzed for nitrogen and chromic oxide, and nitrogen digestion calculated from changes in nitrogen: chromic oxide ratios. Total tract nitrogen digestion coefficients ranged from 62% to 71% and averaged 66.7%. Digestion of nitrogen in the CM ration was significantly (P<.05) lower than that in the CO or MO rations. Prececal nitrogen digestibility ranged from 35.2% to 51.7% and averaged 46%. There were no significant differences among the rations. Nitrogen digestion in the postileal tract was lower than that in the prececal tract, averaging approximately 39%. Ration effects were variable but tended to be in reverse order of pre cecal digestion indicating a compensating effect of the hindgut. Approximately two-thirds of the protein digested was digested and absorbed in the prececal segment of the tract, and the remaining one-third in the postileal segment of the tract. The amount of N, in g/feeding, that disappeared from the small intestine in this study was 22.6, compared to 10.7 g/feeding of N digested from the hindgut. |
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