In situ evaluation of the ruminal and intestinal digestibility of heat-treated whole cottonseeds.

The effect of heating whole cottonseeds on the degradability of DM and CP in the rumen and the small intestine of lactating cows was determined in situ. Whole cottonseeds were heated for 1 or 2 h at 140, 160, or 180 degrees C prior to digestion. The degradation of DM and CP was determined in dacron bags suspended in the rumen for 3, 6, 9, 24, and 48 h. Bags incubated in the rumen for 24 h were introduced into the small intestine through a duodenal cannula and subsequently recovered in feces. The effective ruminal degradabilities of DM and of CP were evaluated, assuming a ruminal outflow rate of .08/h. Heating of whole cottonseeds decreased the degradability of DM and CP in the rumen with a corresponding increase in the amounts digested in the small intestine. The calculated temperature at which this effect was first observed was 130 degrees C. Following optimal heating amount of digestible CP reaching the small intestine more than doubled. The agreement between these findings and the results of previous in vivo experiments suggest that the dacron bag technique may reliably be used for determination of nutrient availability in the intestine.