Increasing atmospheric concentrations of methane have led scientists to examine its sources of origin. Ruminant livestock can produce 250 to 500 L of methane per day. This level of production results in estimates of the contribution by cattle to global warming that may occur in the next 50 to 100 yr to be a little less than 2%. Many factors influence methane emissions from cattle and include the following: level of feed intake, type of carbohydrate in the diet, feed processing, addition of lipids or ionophores to the diet, and alterations in the ruminal microflora. Manipulation of these factors can reduce methane emissions from cattle. Many techniques exist to quantify methane emissions from individual or groups of animals. Enclosure techniques are precise but require trained animals and may limit animal movement. Isotopic and nonisotopic tracer techniques may also be used effectively. Prediction equations based on fermentation balance or feed characteristics have been used to estimate methane production. These equations are useful, but the assumptions and conditions that must be met for each equation limit their ability to accurately predict methane production. Methane production from groups of animals can be measured by mass balance, micrometeorological, or tracer methods. These techniques can measure methane emissions from animals in either indoor or outdoor enclosures. Use of these techniques and knowledge of the factors that impact methane production can result in the development of mitigation strategies to reduce methane losses by cattle. Implementation of these strategies should result in enhanced animal productivity and decreased contributions by cattle to the atmospheric methane budget.

Methane emissions from cattle.

In situ and Other Methods to Estimate Ruminal Protein and Energy Digestibility: A Review

Protein and Energy as an Integrated System. Relationship of Ruminal Protein and Carbohydrate Availability to Microbial Synthesis and Milk Production

Site of Digestion of Starch in the Gastrointestinal Tract of Dairy Cows and Its Effect on Milk Yield and Composition

The Dutch protein evaluation system: the DVE/OEB-system

1. 15 NH 4 Cl was continuously infused for periods of 120–216 h into the rumens of sheep which were allowed to feed 2 out of every 10min. 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. In 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 15 N 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 15 Nin 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 runen. 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/100 g DM fermented. 6. The generation-time of bacterial protein in the rumen was calculated from the rate of in- crease of 15 N 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.

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Nitrogen metabolism in sheep.

1. Six closely shorn sheep were given brome grass (Bromus inermis) pellets at 1 h intervals and maintained at ambient temperatures of --I to Idegree and 18--21degrees for 28 d. Measurements of digestion were made during the last 10 d of temperature exposure. 2. Cold exposure resulted in a reduction in apparent dry matter (DM) digestibility from 0-482 to 0-450, and of apparent digestibility of organic matter (OM) from 0-511 to 0-477. Neither apparent digestibility nor retention of nitrogen was affected. 3. Apparent digestibility of OM in the rumen decreased from 0-300 to 0-242 with cold exposure, and was highly correlated with turnover time in the rumen of 103Ru, which was used as a particulate marker. 4. The efficiency of microbial synthesis (g N incorporated into microbial cells/kg OM apparently digested) was correlated with the dilution rate of the solute marker (51Cr) and with the turnover time of the particulate marker (103Ru) in the rumen. 5. Digestion in the intestine of DM and OM accounted for significantly more of apparent digestion in the whole gastrointestinal tract for sheep kept in the cold than for sheep kept in the warm. The apparent digestibilities of DM and OM entering the intestine were similar in sheep on both treatments, but significantly more non-ammonia-N was digested in the intestines of cold-exposed sheep. 6. The influence of dilution rate of rumen fluid on the efficiency of synthesis of microbial cells in the rumen is discussed.

The effect of cold exposure of sheep on digestion, rumen turnover time and efficiency of microbial synthesis.

1. Three diets of barley-canola-seed (Brassica campestris), lucerne (Medicago sativa) or chopped brome-grass (Bromus inermis) were given at intervals of 3 h to closely-shorn Suffolk wethers held at a temperature of 1-5 degree (cold) or 22-24 degree (warm). Apparent digestibility of organic matter (OM) and nitrogen was reduced by 0.08-0.05 and 0.04 units respectively for lucerne and brome-grass diets given to cold-exposed sheep, but no treatment effects on digestibility were observed for the barley-CSM diet. Measurements achieved using infusion of the digesta markers 58Co-EDTA and 103Ru-phenanthroline (103Ru-P) showed that cold exposure depressed apparent OM digestion in the stomach and intestines by 33 and 42 g/d for the lucerne diet, and 13 and 35 g/d for the brome-grass diet respectively. 2. The turnover time (h) of the 103Ru-P marker in the rumen of warm sheep was 38.9 for barley-CSM, 18.4 for lucerne, and 15.6 for brome-grass. In cold-exposed sheep, 103Ru-P turnover time (h) tended to be reduced to 32.3, 12.3 and 15.3 for the three diets, respectively. OM fermentation in the stomach was highly related to 103RU-P turnover time for lucerne and brome-grass diets. 3. Cold exposure increased the escape of dietary N from the abomasum by 0.04 and 0.09 of dietary N intake for sheep given lucerne and brome-grass diets respectively. Dietary N degradation was closely related to 103Ru-P turnover time for lucerne, and to the proportion of large particles in rumen digesta for the brome-grass diet. Estimates of feed N degradation made by use of information on the rate of fermentation of the diet in nylon bags and 103Ru-P turnover time were consistently lower than those observed in vivo for barley-CSM and lucerne diets. Intestinal digestibility of non-ammonia N was not significantly changed by cold exposure. 4. Transfer of urea from plasma to the rumen was 1.4-2.5 g N/d for the barley-CSM and lucerne diets, but the value for brome-grass was 4.5-4.9 g N/d. Cold exposure did not affect urea transfer. The production of ammonia from feed and endogenous protein was approximately 0.66 and 0.47 g N/g N intake of barley-CSM and lucerne diets, with no effect of cold exposure. Cold exposure reduced the value from 0.57 to 0.38 for brome-grass. 5. The results are compared with those obtained previously with pelleted hay, and the importance of large particle breakdown in the prediction of OM and N fermentation using nylon bags is discussed.

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Effects of cold exposure on feed protein degradation, microbial protein synthesis and transfer of plasma urea to the rumen of sheep

When 103Ru-labelled Tris (1,10-phenanthroline) ruthenium II chloride (103Ru-P) particulate marker in aqueous solution was added to the rumen of four steers given 5.5 kg grass hay/d at two-hourly intervals, the distribution of 103Ru-P marker among rumen particles of various sizes was the same at 4 h, 3 d and 7 d after administration, the concentration of 103Ru-P/g dry matter (DM) was inversely related to particle size and 0.30 of the 103Ru-P was associated with the DM of particles too large to be moved from the rumen at a meaningful rate. Thus, fractional outflow rate (FOR) of 103Ru-P would reflect, but was not a direct measure of, the FOR of the small particle pool in the rumen. When rumen digesta were labelled with 103Ru-P, placed in nylon cloth bags and incubated in vitro with unlabelled digesta, 59% of the 103Ru-P disappeared from the nylon bag in 24 h, and 74% in 48 h. Similar results were obtained when large particles (retained by a 3.2 mm mesh screen during wet sieving) from rumen digesta were subjected to this procedure. In a further experiment, the steers were given the hay in either the long or ground form and drinking water to which 10 g sodium chloride/l were, or were not, added. The FOR of 51CrEDTA in centrifuged rumen fluid was increased (P less than 0.05) from 1.78 to 2.10/d by grinding of the hay diet, but was not influenced by the intake of an additional 257 g NaCl/d. The FOR values of 103Ru-P in mixed rumen digesta and organic 35S in micro-organisms were linearly correlated (P less than 0.05) and were not affected (P greater than 0.05) by grinding and salt treatments. On average, the FOR of organic 35S in micro-organisms was 0.41 of that of 51CrEDTA in centrifuged rumen fluid and 0.85 of that of 103Ru-P in rumen digesta respectively. Grinding of the hay did not (P greater than 0.05) change the proportion of rumen DM (0.476-0.515) or faecal DM (0.107-0.153) retained by the 3.2 mm mesh and larger screens. FOR from the rumen of a given size group of particles was calculated as the ratio, estimated daily flow from the rumen of the size group: rumen pool of the group.(ABSTRACT TRUNCATED AT 400 WORDS)

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Removal of digesta components from the rumen of steers determined by sieving techniques and fluid, particulate and microbial markers

Oxygen consumption and Na+,K+-ATPase(EC 3.6.1.3)-dependent (ouabain-sensitive) and -independent respiration were measured for duodenal mucosa biopsies from 10-month-old sheep given two levels of digestible energy (DE) intake (7.6-7.7 and 14.8 MJ lucerne (Medicago sativa) pellets/d) and following 48 h of starvation. The mucosal biopsies were determined to be structurally intact and free of adherent bacteria on histological and scanning-electron-microscope examinations. The use of D-glucose as a substrate during incubations did not elevate (P greater than 0.05) the respiration indices of the biopsies over those measured during acetate incubations. Glucose uptake did not (P greater than 0.05) influence the Na+,K+-ATPase-dependent respiration of the mucosal biopsies. Na+,K+-ATPase-dependent respiration accounted for 50% of the total O2 consumption of the mucosal biopsies of sheep given the lower level of DE. Total O2 consumption of the duodenal mucosa was not (P greater than 0.05) increased when sheep were given the higher level of DE but Na+,K+-ATPase-dependent respiration of the mucosa was elevated (P less than 0.01) by 37% during this period. When sheep were starved for 48 h, total O2 consumption of the mucosal biopsies was not (P greater than 0.05) affected, however, Na+,K+-ATPase-dependent respiration of the biopsies dropped (P less than 0.01) by 45%. Na+,K+-ATPase-dependent respiration accounted for 61.3% of the O2 uptakes of mucosa from the sheep given the higher level of DE and 28.3% of the O2 uptake of mucosa from fasted sheep.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0007114585001301

L. P. Milligan

Papers

Nitrogen metabolism in sheep.

The effect of cold exposure of sheep on digestion, rumen turnover time and efficiency of microbial synthesis.

Effects of cold exposure on feed protein degradation, microbial protein synthesis and transfer of plasma urea to the rumen of sheep

Removal of digesta components from the rumen of steers determined by sieving techniques and fluid, particulate and microbial markers

Influence of feed intake and starvation on the magnitude of Na+, K+-ATPase(EC 3.6.1.3)-dependent respiration in duodenal mucosa of sheep