Nitrogen transactions in the rumen of sheep given a barley straw diet supplemented with untreated or formaldehyde-treated sunflower seed meal

The effect of formaldehyde treatment of the sunflower seed meal in a barley straw based diet on rumen N transactions was studied in two fistulated crossbred sheep using 15N-ammonia and ¹⁵N- and 14C-urea. Treatment decreased organic matter and N digestibility to a small extent, but substantially decreased urine N excretion so that N retention increased. Treatment resulted in decreases in ammonia and urea synthesis which were reflected in reduced rumen ammonia and plasma urea levels; the net flow of N from the rumen ammonia pool to the plasma urea pool was reduced by 50%. 56-65% of the bacterial N was derived from ammonia. The contribution of bacterial N to N in the protozoal fraction decreased from 45 to 40% in the first sheep, but increased from 35 to 39% in the second; as a consequence, there was a very close relationship (r2 = 0.95) between this parameter and rumen ammonia recycling. Treatment decreased protozoal turnover time in the first sheep, but increased it in the second sheep; this effect may have been due to an increase in lysis of protozoa in the first sheep and a decrease in lysis in the second. Solutes mixed throughout the rumen in from half to one hour.