Rumen Ammonia Levels Research Articles

THE EVOLUTION OF MICROFLORA, MICROFAUNA AND DIGESTION IN THE RUMEN OF LAMBS FROM BIRTH TO 4 MONTHS

In the rumen of lambs, strict anaerobic bacteria dominate as early as 2 days of age. Cellulolytic bacteria appear around the fourth day. Protozoa become established later (2 wk) and their populations have stabilized by 4 mo. Rumen ammonia levels are characteristically high during the first month. Key words: Microflora, protozoa, digestion, rumen, lamb

Effects of lasalocid and monensin on nutrient digestion, metabolism and rumen characteristics of sheep.

Two experiments were conducted to evaluate metabolism and rumen fermentation responses of lambs fed either monensin or lasalocid (33 mg/kg level) in an alfalfa-corn diet. Experiment 1 was a lamb metabolism trial where rumen samples were taken at the end of each excreta collection period. In Exp. 2, ruminally cannulated sheep were used and cotton thread cellulose and soybean nitrogen (N) disappearance were measured by the in situ dacron bag technique. Rumen turnover rates and volatile fatty acid (VFA) and ammonia pool sizes were determined. In Exp. 1, dry matter and fiber (neutral detergent fiber, NDF; acid detergent fiber, ADF and hemicellulose) digestibilities were not influenced by treatment. Absorbed N was increased (P less than .05) with lasalocid, but not with monensin. No direct or adaptive rumen effects on in situ cellulose or N disappearance were noted in Exp. 2 for either additive. In Exp. 1, at 6 h postfeeding, both additives increased (P less than .05) propionate concentration and lowered (P less than .05) the acetate: propionate (A:P) ratio, while only monensin decreased (P less than .05) rumen ammonia levels. However, no differences in ammonia or VFA concentrations were noted at 2 and 4 h postfeeding. In Exp. 2, where pool size was considered, monensin-fed sheep had lower (P less than .05) total quantities of rumen ammonia at 8 and 12 h postfeeding. Both additives decreased A:P ratios at 6 and 12 h. Lasalocid increased (P less than .05) acetate, propionate and total VFA pool size at 12 h.

Utilization of urea and molasses supplements by sheep grazing oat stubble

Mature crossbred wethers, grazed for 11 weeks on oat stubble at a stocking rate of 20 sheep ha-1, were unsupplemented or offered supplements of a urea-mineral block, a molasses lick or a urea-molasses lick. Following rain in the fourth week, half of the area was sprayed with desiccant herbicide to establish weed-free stubbles. The stubble initially yielded c. 2600 kg DM ha-1 of dead crop residues plus 900 kg DM ha-1 of fallen grain; after 11 weeks this had fallen to c. 1400 kg DM ha-1 of dead crop residues. Initially the sheep selected diets of 0.03-0.22 grain and 0.78-0.97 dead herbage and, during this time, urea-supplemented sheep selected diets lower in grain and nitrogen (N) content than those selected by unsupplemented sheep. On weedy stubbles, where green herbage yielded more than 100 kg DM ha-1, sheep selected a diet containing c. 0.78 green herbage (N content 2.6%), ate more digestible organic matter (DOM) and gained more weight than those on weed-free stubbles, where the diets consisted of 0.98 dead crop residues (N content 1.1 %). All sheep ate some of the urea-mineral blocks throughout, but 100% acceptance of the licks only occurred by the 6th week. Mean intakes reached desired levels (10 g urea and/or 50 g molasses sheep-1 day-1) thereafter, but individual intakes varied widely on all supplements, with the coefficient of variation generally > 50%. In most periods, supplementation had only small effects on the intake of DOM. During the first 4 weeks, sheep lost weight except those offered the urea-mineral blocks. Over the whole experiment, urea-supplemented sheep lost less weight than unsupplemented sheep, but this was mainly due to higher weight gains on the weedy plots. Mean concentrations of rumen volatile fatty acids (VFA) were < 80 mmol l-1 throughout, and fell to <40 mmol l-1 on the weed-free plots in the latter stages of the experiment. Mean rumen ammonia levels, which were < 100 mg N l-1 in unsupplemented sheep, were generally increased by urea supplements, and by grazing weedy stubbles. Responses to supplementation are discussed in terms of the quality of the available plant material, the diet selected, the levels of rumen metabolites and the intake of supplements.

Effect of Roasting on Utilization of Soybean Meal by Ruminants

Summary Commercially prepared, solvent-extracted, dehulled soybean meal (SBM) was roasted at five temperatures (102, 128, 144, 159 and 185 C). Roasting at 159 and 185 C increased (P .05) for chicks fed nonroasted, 102, 128 and 144 C SBM. Chicks fed the 159 and 185 C SBM gained less, consumed less dry matter and had reduced gain/ feed (P .05) for lambs fed nonroasted, 102, 128, 144 and 159 C SBM. Roasting SBM at 185 C depressed (P .05) N retention in this study. Rumen ammonia levels were not altered (P>.05) by including roasted SBM in the diet but tended to be lower when roasted SBM was fed. An in situ dacron bag study was conducted to estimate the effect of roasting on the degradation of SBM in the rumen. Although the hour of incubation  SBM interaction was significant, in general, as roasting temperature increased, less N disappeared from the dacron bag, sug

Liver Arginase Activity and Urea Metabolism in Beef Heifers Fed Urea Diets and Abomasally Infused with Arginine and(or) Ammonium Acetate

Eight growing crossbred beef heifers, surgically fitted with indwelling abomasal cannulas, were used in a 4 x 4 Latin square design and examined for the effects of continuous abomasal infusion of arginine and(or) ammonium acetate on liver arginase activity and urea and ammonia metabolism. Heifers were fed complete diets containing 1.2% urea as the only source of supplemental N. Infusion treatments were: (1) control (C): 2 liters water/24 h; (2) arginine (Arg): 24.00 g arginine in 2 liters water/24 h; (3) ammonium acetate (NH4Ac): 116.34 g ammonium acetate in 2 liters water/24 h; (4) arginine plus ammonium acetate (Arg + NH4Ac): 24.00 g arginine . HCl plus 116.34 g ammonium acetate in 2 liters water/24 h. Infusions solutions contained 0, 1, 1 and 2% crude protein equivalent, respectively, above the level of crude protein provided by the diet. NH4Ac and Arg + NH4Ac increased (P less than .05) apparent digestibility of N over that observed with treatment C. Arg tended to increase N retention over that observed with C, while both NH4Ac and Arg + NH4Ac resulted in lower (P less than .05) N retention than did C and Arg. Mean liver arginase activities (mumol . mg protein-1 . h-1) were 166.9, 137.5, 226.3 and 194.5 for heifers infused with C, Arg, NH4Ac and Arg + NH4Ac, respectively. NH4Ac and Arg + NH4Ac resulted in higher (P less than .05) arginase activity than did C or Arg. Arg infusion increased plasma urea N (PUN) over that observed with C, while PUN was higher (P less than .05) with NH4Ac or Arg + NH4Ac than with C or Arg. NH4Ac infusion increased (P less than .05) plasma ammonia-N (PAN) over that observed with Arg or Arg + NH4Ac, while PAN levels were the same with C, Arg and Arg + NH4Ac. Both Arg and NH4Ac infusion resulted in higher (P less than .05) rumen ammonia levels than C, while heifers given Arg + NH4Ac had rumen ammonia levels similar to those of controls. Mean daily urea excretion was 13.16, 16.02, 28.92 and 32.44 g/24 h for heifers infused with C, Arg, NH4Ac and Arg + NH4Ac, respectively. The major difference in excretion of urea was attributable to NH4Ac and not Arg. Daily urea excretion decreased between 1530 and 2330 h and increased between 2330 and 0730 h. Arginine infusion appeared to have a protective effect against ammonia infusion because PUN increased and PAN decreased in heifers infused with arginine. The reduction (P less than .05) in plasma amino acids thought to be limiting for protein synthesis in ruminants in conjunction with increased (P less than .05) N retention and the trend toward decreased arginase activity observed in heifers infused with Arg suggests that the effects of arginine on ammonia metabolism are not wholly mediated by liver urea synthesis.

Changes in rumen fluid composition and in the rumen epithelium when wheat is introduced to the diet of sheep: the influence of wheat and hay consumption

The effects of the levels of wheat and of hammermilled hay fed to sheep on ruinen acidity and ammonia concentration were determined during the first 4 days of feeding wheat. Consumption of wheat reduced rumen pH, but the effect diminished with time, so that by day 4 it was not significant. Wheat intake also significantly (P < 0.05) increased rumen ammonia on day 1, but not during days 2-4. Volatile fatty acid (VFA) concentrations on day I were increased (P < 0.05) by wheat intake, the effect being less on later days. The proportion of acetate was reduced (all days). while propionate (days 1, 2 and 4) and butyrate (days 3 and 4) were increased by the consumption of wheat. Concentrations of lactate (mainly the D-isomer) increased after wheat was fed, although wheat level per se did not significantly affect lactate concentrations. Peak concentrations of lactate occurred on day 2 (18 m~ total lactate). Initially, consumption of hay decreased rumen pH and had little effect on ruman ammonia levels. By day 4, hay consumption was associated with increases in rumen pH and decreases in rumen ammonia levels (0.006 units and -0.05 mM per g hay dry matter (DM) respectively). Concentrations of VFA tended to be increased by hay consumption, but the proportions of the major VFAs were not affected. Hay intakes on day 4 were associated with reductions in rumen total lactate concentrations of 51 �M per g hay DM. Reduced total DM intakes of sheep eating ad libitum were associated with low rumen pH and high lactate concentrations. Microscopic lesions were observed on the rumen papillae of sheep 7 days after wheat was first fed. The extent of these lesions was reduced by hay intake, and was also related to the minimum pH observed.

Utilization of low quality roughages: effects of urea and protein supplements of differing solubility on digesta flows, intake and growth rate of cattle eating oaten chaff.

1. Expt 1. Five 150 kg steers with ruminal, abomasal and ileal cannulas were given 3000 g oaten chaff daily plus pelleted supplement with no added nitrogen (diet A) of 50 g N/d as urea (diet B), casein (diet C), casein and formaldehyde-treated casein (HCHO-casein) (50:50 w/w; diet D) and HCHO-casein (diet E), in a 5 x 5 Latin square design. The basal diet and supplement were fed in eight equal increments at intervals of 3 h. Proportions of dry matter and organic matter digested in the stomach and whole tract were greater for diets B, C, D and E than for diet A. Total volatile fatty acid levels in the rumen and the proportion of acetic acid, were lower, and the proportion of propionic acid higher on diet A than on the other diets. Rumen ammonia levels were lower on diets A, D and E than on diets B and C. N flows at the abomasum, ileum and rectum were lower on diet A than on the other diets; abomasal flows and apparent intestinal absorptions of amino acids were higher on diets D and E than on diets A, B and C. Efficiencies of bacterial protein synthesis were 15, 15, 14, 13 and 12 g bacterial N/kg OM truly digested in the stomach on diets A, B, C, D and E respectively. 2. Expt 2. Forty 300 kg steers were fed oaten chaff ad lib. plus twice the amount of the same pelleted supplements as in Expt 1. Intake of oaten chaff was 23% higher with N supplements (diets B, C, D and E) than without (diet A). Live-weight gains were 356, 798, 843, 842 and 805 g/d on diets A, B, C, D and E respectively. 3. It was concluded that efficiency of bacterial protein synthesis was not limited by the supply of peptides and amino acids in the rumen, and that increases in amino acid availability in the intestines from feeding HCHO-casein did not increase food intake or live-weight gain.

Effect of lactose supplement on digestion of lucerne hay by sheep. I. Sites of organic matter and nitrogen digestion.

Lactose was added (400 g/day, as powder) to a lucerne hay diet (700 g/day, chopped). The two diets (hay and hay with lactose) were fed twice daily, successively, to four adult sheep fitted with rumen cannulas and simple cannulas at the proximal and at the distal end of the small intestine. Organic matter (OM) intake was 544 g/day with hay and 961 g/day with hay and lactose. Addition of lactose increased the proportion of OM that disappeared within the rumen (45.7 vs 38.7%) and within the small intestine (18.3 vs 13.2%), and decreased amounts that disappeared in the large intestine (6.7 vs 9.0%). However, the differences were not significant. Lactose was almost entirely fermented in the rumen, resulting in low pH and high lactate concentration for 3 hr after meals. Mean volatile fatty acid (VFA) concentrations were low (67 mmoles/liter) and unchanged by addition of lactose. Propionate and valerate molar proportions increased and acetate molar proportions decreased with lactose supplementation. Adding large amounts of readily fermentable carbohydrates as lactose greatly altered nitrogen digestion of the lucerne hay in the rumen; supplementation allowed a greater uptake of ammonia for microbial synthesis. Consequently, rumen ammonia levels, blood urea and urinary nitrogen excretion decreased greatly with lactose, from 20.5 mg/100 ml, 20.6 mg/100 ml and 6.96 g/day to 2.3 mg/100 ml, 8.7/100 ml and 2.5 g/day, respectively. The amount of nitrogen flowing into the duodenum increased by 47%, and the amount of nonammonia nitrogen apparently digested within the small intestine by 83%. Nitrogen in feces increased with lactose because of increased microbial nitrogen. Retained nitrogen increased only slightly (from 5.0 to 6.4 g/day) because of the low nitrogen needs of sheep.

Slow ammonia release from urea: rumen and metabolism studies.

A new slow-release urea (SRU) made by coating prilled urea with a tung oil-linseed oil-talc-catalyst mixture was evaluated for ammonia-nitrogen release rate, animal acceptability, toxicity and effects on dry matter digestibility, diet intake and nitrogen retention. When added at a level equal to 1% urea in an 80% concentrate steer diet and fed twice daily, SRU gave a ruminal ammonia-nitrogen peak 1 hr postfeeding of 32 mg/dl compared to a peak from prilled urea of 53 mg/dl at 30 minutes. Bi-hourly feeding of prilled urea and SRU produced similar rumen ammonia-nitrogen levels and demonstrated that SRU was almost completely hydrolyzed in the rumen. Steers fasted for 26 hr and refed with supplements containing 10% urea from prilled urea had rumen ammonia levels of 120 ml/dl and showed muscle tremors 35 min after feeding. Rumen ammonia levels of steers fed equivalent urea from SRU remained below 35 ml/dl and exhibited no toxicity symptoms. Sheep fed ad libitum cottonseed hulls were offered a supplement containing 5% or 10% urea from urea or SRU once daily. Intake of SRU supplement was 7 and 17% greater, while cottonseed hull intakes were similar for sheep fed urea or SRU at the 5 and 10% levels. In a nitrogen balance trial, steers were fed ad libitum cottonseed hulls unsupplemented or supplemented with isonitrogenous amounts of SRU, prilled urea or soybean meal. Added nitrogen from all sources increased cottonseed hull intake. Steers fed SRU consumed more (P less than .05) cottonseed hulls than steers fed urea. Dry matter digestibility and nitrogen retention values tended to be highest for steers fed soybean meal supplement with little difference noted between prilled urea and SRU supplements.

Maize for silage II. The effect of urea and acid as preservative treament on rumen fermentations and on feeding values of silages

The rumen fermentations and N-balances of rumen fistulated sheep were studied on diets of silages treated with urea and acid preservative. The digestibilities and feeding values of the silages were also calculated. The experiment was performed according to 5 x 5 Latin-square design. The digestibilities were determined by total collection the collection period lasting seven days. The rumen samples were taken on the last two days during the collection periods before and 1.5, 3.0, 4.5 and 6.0 hours after feeding. Besides the silages the animals received mineral mixture and water ad libitum. Urea or acid treatment had no effect (P > 0.05) on the consumption of silage DM. The consumption ranged from 1.7 to 1.9 kg DM/100 kg liveweight. Urea did not have a clear effect on the VFA production in the rumen. It tended, however, to decrease the proportions of C3 and C4—C5 acids in the rumen. Acid preservative decreased the production of VFA and the proportion of C3-acid (P < 0.05) in the rumen. The proportion of C3-acid was higher respectively, (P < 0.05). The rumen ammonia levels were extremely high, 60—80 mg/100 ml, after feeding with urea treated silages. This was possibly partly due to the relatively short (14 days) adaptation time before collection period. The urea or acid preservative treatment gave no clear responses regarding the apparent digestibility values of the silages. The DCP values were highest (P < 0.05) in the urea treated silages, but no differences (P > 0.05) were found between the energy values, which varied between 0,12—0.14 f.u./kg of silage. There were no differences in the N-balances of the animals on different diets. The balances were positive on all diets.

The effect of formaldehyde treatment before ensiling on the digestion of wilted grass silage by sheep

1. Wilted perennial ryegrass (Lolium perenne L. cv. Endura) was ensiled without additive or after addition of a mixture of equal volumes of formic acid (850 g/kg) and formalin (380 g formaldehyde/kg) applied at a rate of 35 g formaldehyde/kg herbage crude protein (nitrogen x 6.25). The digestion of the two silages and the effect of supplemental N as urea or urea plus soya-bean meal on the digestion of the treated silage was studied using sheep fitted with a rumen cannula and re-entrant cannulas in the proximal duodenum and distal ileum. 2. The additive markedly reduced carbohydrate fermentation and protein degradation in the silo. 3. There were no significant differences between diets in rumen pH, dilution rate, volatile fatty acid production and the molar proportions of acetate, propionate and butyrate. However, rumen ammonia levels and the apparent digestibility of organic matter (OM), gross energy (GE) and cellulose in the stomach were significantly depressed (P less than 0.05) by the additive. It also reduced (P less than 0.05) the extent to which the N of the silage was degraded in the rumen and, with the treated silage, more microbial N was synthesized in the rumen than food N degraded, resulting in a net grain of N between mouth and duodenum, as compared to a net loss with the untreated silage. 4. Supplementation of the treated silage with urea or urea plus soya-bean meal significantly increased (P less than 0.05) the amount of food N degraded in the rumen and rumen ammonia levels but had no effect on the apparent digestibility of OM, GE and cellulose in the stomach or on the amount of microbial N reaching the duodenum. 5. The quantity of microbial amino acids entering the small intestine and the apparent digestibility of amino acids in the small intestine were similar for all four diets. However, the quantity of food amino acids reaching the small intestine was significantly higher with the three diets containing the treated silage and consequently the apparent absorption of amino acids from the small intestine was substantially higher with these diets than with the untreated silage.

The digestion of barrel medic (Medicago truncatula) hay and seed pods by sheep

Experiments were conducted to determine the digestion and utilization of barrel medic hay and pod fed separately to penned sheep. Estimates were made of intake and digestion in the whole tract. Rates of passage of digesta from the stomach and intestines were estimated by reference to radioactive markers. The organic matter of pod contained 23.8% crude protein, 5.2% long-chain fatty acids and 77.5% acid-detergent fibre including 19.9% lignin. Organic matter digestibility was only 24.3%, largely because of poor digestibility of fibre. Protein utilization was inefficient because of high loss of dietary protein in the rumen and poor digestibility in the small intestine. Only 20.3% of protein intake was absorbed from the small intestine. High loss of protein in the rumen was verified by high rumen ammonia levels, 52 mg nitrogen/100 ml rumen liquor. Long-chain fatty acids present in the pod diet, mainly in polyunsaturated form, were extensively hydrogenated in the stomach. Although only a small loss of fatty acids occurred in the stomach, 72% of the intake was absorbed from the small intestine. Pods provided only small amounts of nutrients, derived mainly from the digestion of seeds. However, energy derived from pods should be used efficiently, as a high proportion of absorbed nutrients consisted of long-chain fatty acids and amino acids. Barrel medic hay had an organic matter digestibility of 65% and contained 16.9% crude protein. Digestibility of organic matter in the stomach and intestines resembled that of lucerne, and it was concluded that barrel medic hay was similar in nutritive value to good quality lucerne hay.

A note on rumen ammonia and blood urea levels in steers administered urea or sparingly soluble urea derivates as nitrogen supplements

SUMMARYRuminal ammonia and blood urea levels were compared in fistulated steers eating paddy straw to appetite and given urea alone, urea plus oxalate, and complexes of urea with either formaldehyde (UFC) or oxalate (UOC), introduced into the rumen in a single daily dose. The solubilities of UFC and UOC in rumen liquor were 23·7 and 4·6% respectively of that of urea. Higher levels of ruminal ammonia and blood urea were recorded on urea than on other supplements.

Formaldehyde treatment of concentrate diets for sheep. II.* Effect on urea synthesis and excretion

The synthesis of urea, its return to the gastrointestinal tract and excretion in the urine were studied in sheep given concentrate diets, untreated or treated with formaldehyde, containing four different protein levels. Rumen ammonia and plasma urea levels increased with protein level and decreased with formaldehyde treatment. Changes in urea excretion were closely related to changes in plasma urea levels. There was a relationship between urea synthesis and rumen ammonia levels, but differences in the amount of urea returned to the gastrointestinal tract did not follow a consistent pattern. When expressed as a percentage of urea synthesized, urea recycling decreased as protein level increased but tended to increase when the diets were treated. The results are consistent with an appreciable fraction of the nitrogen returned to the rumen being in forms other than urea. _________________ *Part I, Aust. J. Agric. Res., 28: 1055 (1977).

Formaldehyde treatment of concentrate diets for sheep. I. Partition of the digestion of organic matter and nitrogen between the stomach and intestines

The effect of formaldehyde treatment of barley/soybean meal diets was studied in fistulated crossbred sheep at four protein levels. The overall digestion of organic matter was similar for all diets; the small differences in the partition of organic matter digestion in response to treatment were not significant. Dietary starch was completely digested. The partition of starch digestion was variable but was not affected by protein level or treatment. The relationship between nitrogen intake and the amount of non-ammonia nitrogen (NAN) digested in the intestines was curvilinear; NAN digested was calculated to reach a maximum when 17.4% of the dietary organic matter was crude protein. Formaldehyde treatment substantially increased the amount of NAN digested in the intestines; a treated diet in which 12.6% of the organic matter was crude protein would provide the same amount of NAN digested as the 17.4% untreated diet. The apparent digestibility of NAN in the intestines was not affected by protein level or treatment; treatment at the highest protein level appeared to cause a reduction in true digestibility to 0.75 from the mean of 0.80 obtained for the other diets. Treatment appeared to have no consistent effect on the efficiency of bacterial protein synthesis. The flows of water and of digesta from the rumen and abomasum were not affected by protein level or treatment; differences between sheep were responsible for much of the variance in these parameters. The treatment reduced rumen ammonia and volatile fatty acid levels and plasma urea levels. Neither the amount and composition of the long-chain fatty acids reaching the intestine nor their digestion there were affected by the treatment.

Studies on the adaptation of the rumen to the hydrolysis of biuret in cattle

SUMMARYStudies on the adaptation of cattle to the hydrolysis of biuret and on the response of rumen ammonia level to the introduction of 50, 100 or 150 g of feed-grade biuret showed that (1) the rate of ruminal adaptation to the hydrolysis of biuret increased to a maximum effective level of about 350 mg/24 h/100 ml within 10 days when a readily available energy source was fed, (2) a single dose of 50, 100 or 150 g/day of biuret was associated with a prolonged increase of rumen NH3 concentration. The magnitude of the increase was 8–9 mg/100 ml for every 50 g of added biuret, (3) adapted rumens retained their biuretolytic activity for several weeks, and responded to the re-introduction of biuret into the diet by increasing to a near maximum rate within 24–48 h.

A study of feeding types and certain rumen functions in six species of South African wild ruminants

SUMMARYIn order to characterize the rumen digestive physiology of South African wild ruminants investigations were made on a total of 35 individuals of six species killed in various regions during the dry season.In buffalo, blue wildebeest and gemsbok grasses constituted 85–100% and in impala, springbok and kuduless than 10% of the diet. In the case of the latter three species effects of the habitat and of predilection for certain plant materials were apparent.Compared with the grazers, the species feeding mainly on plant material other than grass were characterized by a smaller physiological capacity of the rumen reticulum, higher counts of ciliate protozoa and ‘large bacteria’, higher levels of rumen ammonia and higher molar proportions of rumen propionate and valerate. Within these feeding types differences between species were indicated.

The proportion of dietary protein escaping degradation in the rumen of sheep fed on various protein concentrates

The 35S content of ruminal microbial protein following intraruminal infusions of Na235SO4 was used to estimate the relative proportions of microbial and dietary protein in the duodenal digesta of sheep, and hence the proportion of the dietary protein which escaped microbial proteolysis in the rumen. When sheep were given a protein-free diet, the mean ratio of the specific activities of the sulphuramino acids in the duodenal microbial fraction (M) and the unfractionated duodenal digesta (D) was 0.97 ? 0.08 and 1.00 ? 0.06 in two separate experiments. When zein was included in the diet the ratio M/D increased to 2.35 ? 0.14, which indicated that 44 ? 3.4% of nitrogen in the duodenum was microbial. When casein was offered, the ratio M/D was 1.12 ? 0.05, which indicated that 91 ? 6.7% of duodenal nitrogen was microbial. When sheep were offered a partially purified diet containing fish meal, lupin meal, peanut meal or soya bean meal, the ratio MID indicated that 29, 65, 63 and 39% of the fish meal, lupin meal, peanut meal and soya bean meal, respectively, was degraded in the rumen; rumen ammonia levels (mg nitrogen/100 ml fluid) were 8.3, 20.9, 16.0 and 6.5, and nitrogen balances were 5.0, 2.4, 2.9 and 5.4 g/day respectively. The 35S-incorporation technique appears to provide realistic estimates of the proportions of dietary proteins which escape degradation in the rumen.

The effect of formaldehyde treatment of a casein supplement on urea excretion and on digesta composition in sheep

The urinary excretion of urea, the fate of an intravenous dose of urea, overall nitrogen metabolism and the composition of rurnen and abomasal samples were studied in crossbred sheep given a basal roughage diet to which supplements of starch, casein or formaldehyde-treated casein were added. Urea excretion was closely related to plasma urea level (r = 0.935) and to the filtered load of urea (r = 0.957). The amount of urea reabsorbed by the kidney increased as'the amount filtered increased; the relationship was improved when values obtained at urine flow rates less than 1 rnl/rnin were omitted. When sheep were given the starch and treated casein diets, the rate at which they cleared a small dose of urea from their plasma was greater than the renal clearance rate; only 75% of a large dose was recovered in the urine. The capacity to dispose of exogenous urea by extra-renal pathways was apparent only when rumen ammonia nitrogen levels were less than about 200 mg/l. Formaldehyde treatment reduced nitrogen digestibility but reduced urine nitrogen excretion to a greater extent so that nitrogen retention increased. Treatment was associated with reduced plasma urea levels, reduced rumen and abomasal ammonia levels, reduced total VFA levels, increased proportions of acetic acid and decreased proportions of isobutyric, isovaleric and n-valeric acids, and more protein in abomasal contents.

Corrigendum - The effect of formaldehyde treatment of a casein supplement on urea excretion and on digesta composition in sheep

The urinary excretion of urea, the fate of an intravenous dose of urea, overall nitrogen metabolism and the composition of rurnen and abomasal samples were studied in crossbred sheep given a basal roughage diet to which supplements of starch, casein or formaldehyde-treated casein were added. Urea excretion was closely related to plasma urea level (r = 0.935) and to the filtered load of urea (r = 0.957). The amount of urea reabsorbed by the kidney increased as'the amount filtered increased; the relationship was improved when values obtained at urine flow rates less than 1 rnl/rnin were omitted. When sheep were given the starch and treated casein diets, the rate at which they cleared a small dose of urea from their plasma was greater than the renal clearance rate; only 75% of a large dose was recovered in the urine. The capacity to dispose of exogenous urea by extra-renal pathways was apparent only when rumen ammonia nitrogen levels were less than about 200 mg/l. Formaldehyde treatment reduced nitrogen digestibility but reduced urine nitrogen excretion to a greater extent so that nitrogen retention increased. Treatment was associated with reduced plasma urea levels, reduced rumen and abomasal ammonia levels, reduced total VFA levels, increased proportions of acetic acid and decreased proportions of isobutyric, isovaleric and n-valeric acids, and more protein in abomasal contents.