NITROGEN TRANSACTIONS IN THE RUMEN OF SHEEP GIVEN A BARLEY STRAW DIETSUPPLEMENTED WITH UNTREATED OR FORMALDEHYDE-TREATED SUNFLOWER SEED MEAL

The effect of formaldehyde treatment of the sunflower seed meal in a b arley straw based diet on rumen N transactions was studied in two fist ulated crossbred sheep using N-15-ammonia and N-15- and C-14-urea. Tre atment decreased organic matter and N digestibility to a small extent, but substantially decreased urine N excretion so that N retention inc reased. 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 decre ased from 45 to 40% in the first sheep, but increased from 35 to 39% i n the second; as a consequence, there was a Very close relationship (r (2) = 0.95) between this parameter and rumen ammonia recycling. Treatm ent decreased protozoal turnover time in the first sheep, but increase d 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 th e second. Solutes mixed throughout the rumen in from half to one hour.