NITROGEN METABOLISM AND FLOW OF NITROGENOUS COMPOUNDS THROUGH THE GASTROINTESTINAL TRACT OF SHEEP FED FORMALDEHYDE-TREATED RAPESEED MEAL

Abstract

Four mature wether sheep weighing 45–50 kg and fistulated in the abomasum and in the terminal ileum with plastic cannulas were used to determine the effect of formaldehyde treatment of rapeseed meal on the digestibility of nutrients and flow of nitrogenous compounds through the gastrointestinal tract. The sheep were fed four pelleted diets containing 8 or 16% rapeseed meal treated with water or formaldehyde at 1 g formaldehyde/100 g crude protein in a 4 × 4 latin square design. Urea was added to the diets containing 8% rapeseed meal at a level calculated to make all diets isonitrogenous; however, the actual N level of the formaldehyde-treated 8% rapeseed meal diet was somewhat higher than for the other diets. The animals were offered 600 g of feed twice daily at 12-h intervals. Formaldehyde treatment of rapeseed meal did not significantly affect the apparent digestibility of crude protein or dry matter of the experimental diets. No significant differences were observed in total N excretion, or N retention among the four treatments. However, N retained, expressed as grams or as a percentage of absorbed N, for the diets containing formaldehyde-treated rapeseed meal tended to be higher than for the diets containing water-treated rapeseed meal. Formaldehyde treatment of the 16% rapeseed meal diets moderated the increases in rumen fluid ammonia and blood urea N levels following feeding. Formaldehyde treatment of the 16% rapeseed meal diet also increased the flow of dry matter, total N (P < 0.01), and true protein N (P < 0.05) in the abomasal digesta of sheep compared to those fed the water-treated rapeseed meal diet. A similar, but nonsignificant (P > 0.05), effect of the formaldehyde treatment was observed in the ileal digesta of the sheep.