Nitrogen metabolism in sheep

Abstract

I. 15NH4C1 was continuously infused for periods of 120-216 h into the rumens of sheep which were allowed to feed 2 out of every 10 min. These treatments achieved steady metabolic states and allowed the assessment of nitrogen conversions by means of tracer methodology. The sheep were given either a barley diet or one of three hay diets. I n two trials, the flow of abomasal material was determined using lignin and polyethylene glycol as markers. The amounts of dry matter (DM), gross energy, total N, soluble N, microbial N and microbial DM in abomasal digesta, and the concentration of ammonia in the rumen liquor were measured. The concentrations of lSN in the N of urine, faeces, rumen and abomasal bacteria and protozoa, rumen and abomasal bacterial and protozoal protein, abomasal particulate matter and in rumen ammonia were determined.2. Comparisons of the steady-state concentrations of I6N in the microbes with that in rumen ammonia indicated that from 50 to 65 % of the bacterial N and from 31 to 55 % of the protozoal N were derived from rumen ammonia in vivo.3. An amount of N equivalent to 60-92 % of the daily intake was transformed into ammonia N in the nunen. 4. Some 17-54% of the ammonia was absorbed from the rumen, but this was not readily converted into urea.5. Microbial growth in the rumen resulted in the assimilation of 1.7-2.6 g N/IW g DM fermented.6. The generation-time of bacterial protein in the rumen was calculated from the rate of increase of 16N concentration in this fraction, and values of 38 and 42 h were obtained for sheep given barley and hay diets respectively. 7.The combined results allowed quantitative estimates to be made of the complete metabolism of rumen N, and from these the possibility of fixation of N gas in the rumen was suggested.Ammonia may be produced in the rumen from either protein (Blackburn & Hobson, 1960), or urea (Huhtanen & Gall, 1955) which enters in the saliva (Somers, 1961) or by diffusion across the rumen wall (Houpt, 1959), or from non-protein nitrogen sources other than urea (Blackburn, 1965).The results of numerous experiments have shown that rumen micro-organisms utilize ammonia for cell synthesis (Hungate, 1966). Bryant & Robinson (1962) found that ammonia is a preferred source of N for a large number of rumen organisms, and that it is essential for growth in some species.The experiments described in this paper were designed to study in vivo the quantitative importance of rumen ammonia for the synthesis of nitrogenous material in rumen microbial cells, a topic which Hungate (1966) described as 'one of the most intriguing problems in rumen ecology'. In addition, two experiments were undertaken to determine the quantity of plant and microbial material passing through the abomasum. 24

Quantitative microbial protein synthesis in the bovine rumen

“…Synthesis per 100 g OMD with the corn diet was 1,3 -1.6 times that observed with the cob diet. The results of this dietary carbohydrate source comparison seem to be in agreement with the work by Mathison and Milligan (1971) who observed 1,1 to 1,3 times more synthesis per 100 g OMD with a barley diet than with a hay diet.…”

“…No explanation for this was given. Mathison and Milligan (1971) estimated microbial synthesis in the rumen following separation of microbial and feed protein in digesta sam ples by an elaborate technique. ^^NH^Cl was continuously infused into the rumens of sheep.…”

Nitrogen cycling in sheep

“…Ammonia production in the rumen has been measured directly in three studies (see Pilgrim et al 1970;Mathison & Milligan, 1971 ;Nolan & Leng, 1972). T h e concentration of ammonia in rumen fluid of sheep fed roughage diets varied between 60 and 290 mg N/l but the ammonia irreversibly lost was approximately constant at I I g Nfd (8-17 g) in all three studies.…”

Ruminal degradation of switchgrass, big bluestem, and smooth bromegrass leaf proteins

“…Ruminally degraded protein in excess of microbial requirements results in nitrogen ( N ) loss as ammonia (Mathison and Milligan, 1971) and inefficient N utilization by ruminants (Storm et al, 1983). Warmseason (C,) grasses tend t o be more slowly degraded in the rumen than cool-season (CS) grasses (Minson and McLeod, 1970;Van Soest, 1982).…”