Rumen Fluid Dilution Rate Research Articles

Effect of quantity and source of rumen nitrogen on the efficiency of microbial protein synthesis in steers consuming tropical forage

Low values for the efficiency of microbial protein synthesis (EMPS) in cattle consuming tropical forages are related to low rumen degradable crude protein (RDP) intakes. This study examined the effect on the EMPS of the quantity and source of nitrogen (N) supplied to the rumen of eight entire and four rumen-fistulated Brahman steers consuming mature tropical grass hay (57.3 g crude protein/kg DM). Four treatment diets were fed in a Latin square design and included a basal diet of mature pangola grass (Digitaria eriantha) hay (control) and hay plus supplements estimated to provide 150 g RDP/kg digestible organic matter intake (DOMI), as urea or casein, or 300 g RDP/kg DOMI as casein. The EMPS was only increased (P < 0.05) above that for the control diet (167 vs 123 g microbial crude protein (MCP)/kg DOMI) when RDP was provided at the highest rate of 293 g/kg DOMI. This increase was also associated with an ~4-fold increase in the concentration of NH3-N (277 vs 73 mg/L) and of branched-chain volatile fatty acids (44 vs 10 mmol/mol of total volatile fatty acids) in rumen fluid of the steers. However, the source of rumen degradable N (urea or casein) had no effect on the EMPS (109–115 g MCP/kg DOMI) when supplied at ~150 g RDP/kg DOMI. There was no effect of treatment on in vivo neutral detergent fibre digestibility (599 g/kg DM) or the rate (0.037/h) or extent (potential degradable fraction: 636 g/kg OM) of in sacco disappearance of pangola grass hay. In addition, rumen particle dilution rate was unaffected by treatment (0.022/h) and rumen fluid dilution rate, although showing some treatment differences (0.048–0.062/h), was poorly correlated with EMPS. It was concluded that only high amounts of RDP supply to the rumen, in the form of true protein, resulted in increased EMPS whereas at the lower intakes of RDP formulated to achieve EMPS in the range suggested in the feeding standards (130–170 g MCP/kg DOMI) there was no difference in providing the RDP as non-protein N or degradable-protein.

Efficiency of rumen microbial protein synthesis in cattle grazing tropical pastures as estimated by a novel technique

The efficiency of microbial protein synthesis (EMPS) in cattle grazing a range of tropical pasture types was examined using a new method of intra-jugular infusion of chromium–EDTA to estimate urinary excretion of purine derivatives. Seven pasture types were studied in south-eastern Queensland, Australia, over a 13-month period. These included native tropical grass (C4) pasture (major species Heteropogon contortus and Bothriochloa bladhii) studied in the early wet, the wet–dry transition and the dry season; introduced tropical grass (C4) pasture (Bothriochloa insculpta) in the mid-wet season; two introduced tropical legume species (C3; Lablab purpureus and Clitoria ternatea); and the temperate-grass (C3) pasture, ryegrass (Lolium multiflorum). There was a large range in EMPS across pasture types, with a range of 26–209 g microbial crude protein per kilogram digestible organic matter intake (DOMI). Estimated rumen-degradable protein (RDP) supply (42–525 g/kg DOMI) was the major factor associated with EMPS across the range of pasture types studied. EMPS in steers grazing all tropical grass pastures was low (<130 g/kg DOMI) and limited by RDP supply. Negative linear relationships (P < 0.05) between EMPS and concentrations of both neutral detergent fibre and acid detergent fibre in extrusa were evident. However, non-fibre carbohydrate in extrusa, total non-structural carbohydrate concentration in plucked pasture leaf, rumen fluid and particle dilution rate, protozoal concentration in rumen fluid and rumen fluid pH were not correlated with EMPS. It was concluded that EMPS was well below 130 g microbial crude protein per kilogram DOMI when cattle grazed unfertilised, tropical grass pastures in south-eastern Queensland and that RDP was the primary limiting nutrient. High EMPS was associated with a very high RDP, vastly in excess of RDP requirements by microbes.

Effects of energy and protein supplementation on microbial-N synthesis and allantoin excretion in sheep fed guinea grass

An experiment was conducted to determine the effects of two types of protein, soybean meal (SBM) and fish meal (FM); and two types of energy supplements, corn flour (CF) and paper pulp (PP) on in vivo digestibility of organic matter (OM), rumen fermentation pattern and dilution rate, rumen microbial-N synthesis and flow of organic matter and nitrogenous compounds through the duodenum in four Merino rams with an average weight of 54.4±4.5 kg. The relationships between duodenal purine flow and urinary allantoin and duodenal protein/energy (MJ rumen VFA per day) ratio were also investigated. The experiment was conducted in a 4×4 Latin square design with a 2×2 factorial arrangement of dietary treatments. The animals, fitted with both rumen and duodenal cannulae were housed in individual crates and fed chopped fresh guinea grass ad libitum twice daily, 100 g molasses and one of the four dietary supplements: (i) 170 g FM+268 g PP (FM+PP); (ii) 170 g FM+268 g CF (FM+CF); (iii) 200 g SBM+200 g PP (SBM+PP); and (iv) 200 g SBM+200 g CF (SBM+CF). Each supplement, at varying rates of rumen degradability, was formulated to provide similar amount of N and gross energy. The results showed that rumen pHs were similar, ranging from pH 5.8 to 6.0, for all animals fed the different dietary supplements. Rumen ammonia concentration was significantly ( p<0.05) higher in animals fed SBM (170.2–190.7 mg N l −1) than in animals fed FM supplement (166.8–170.2 mg N l −1). Rumen VFA concentrations were similar (94–103 mM) but molar proportions of acetate and propionate were respectively lower and higher in treatment SBM+CF, leading to a significantly decreased acetate:propionate ratio in this treatment (3.6) compared to SBM+PP (4.3). There were no significant differences between treatments in rumen fluid dilution rate and rumen volume. Duodenal OM flow was similar in PP supplemented diets, but differed significantly ( p<0.05) between protein supplements in the CF diets. Organic matter digestibility in the rumen was significantly ( p<0.05) higher in the CF+FM diet. Moreover, animals fed SBM supplement showed higher total tract OM digestibility than animals fed FM supplement. The flow of nitrogenous compounds to the duodenum, i.e., total-N, non-ammonia-N and rumen-undegradable-N were not significantly affected by either protein or energy supplements. Microbial-N flow tended ( p<0.08) to be higher in sheep fed CF supplement (average of 10.2 g per day) than in those fed PP supplement (average of 8.1 g per day). Urinary allantoin excretion was low (0.30–0.42 mmol per day/kg BW 0.75). A positive linear correlation ( r=0.73, p<0.005) between urinary allantoin (μmol per day/kg BW 0.75) and duodenal purines (μmol per day/kg BW 0.75) was observed. The efficiency of rumen microbial-N synthesis based on OM truly digested in the rumen was significantly ( p<0.02) higher in sheep fed CF supplement (15.2–16.6 g N kg −1 OMTDR) than in those fed PP supplement (12.2–12.8 g N kg −1 OMTDR). Differences in microbial protein:energy ratio or total duodenal protein:energy ratio among dietary treatments were not significant.

Effects of Protein and Carbohydrate Supplements on Feed Digestion in Indigenous Malaysian Goats and Sheep

Experiments were conducted to determine the effects of soybean meal (SBM) as a source of protein and sago meal (SM) as a source of carbohydrate on in situ and in vivo digestibility of dietary components in four male goats (Kambing Katjang) and four male sheep (Malin) weighing 25-35 kg. Rumen volume, as well as rumen fluid dilution rate were also determined. The animals were housed in single pens with individual feeding and drinking troughs and each animal was fitted with a rumen fistula. They were fed two diets : chopped rice straw+200 g soybean meal (SBM), and chopped rice straw+190 g soybean rneal+300 g sago meal (SBM+SM). Rice straw was offered ad libitum. The supplements were isonitrogenous (80 g crude protein/animal/d), but the proportions of dry matter (DM), organic matter (OM), crude fibre (CF), neutral detergent fibre (NDF) and acid detergent fibre (ADF) were lower in the SBM supplement (191, 165, 11, 40, 15 g/animal/d for DM, OM, CF, NDF and ADF, respectively) than in the SBM+SM supplement (445, 423, 25, 102, 38 g/animal/d for DM, OM, CF, NDF and ADF, respectively). Two animals from each species were fed either supplement in a cross-over design in two periods. Each period lasted for four weeks. In situ and in vivo digestibility studies were carried out, followed by the determination of rumen volume and rumen fluid dilution rate. The results showed that straw DM and total DM intakes of goats (average of 48.7 g/kg W0.75, 72.7 g/kg W0.75, respectively) were significantly (p<0.01) higher than sheep (average of 35.6 g/kg W0.75, 61.6 g/kg W0.75, respectively), but OM, N and GE intakes were not significantly different between the two animal species. When the effect of supplements was compared, animals fed SBM+SM supplement had significantly (p<0.001) higher DM, OM and GE intakes than animals fed SBM supplement. Potential degradabilities of rice straw DM were significantly (p<0.01) higher in goats (average of 48.8%) than in sheep (average of 46.1%). The supplements had no significant effect on the potential degradabilities of DM, OM and NDF, but they had a significant (p<0.05) effect on the degradation rates of DM and NDF. The addition of sago meal in the diet reduced the degradation rates of DM and NDF of rice straw in the rumen. Potential degradability of DM of soybean meal was not significantly different between animal species as well as between supplements. Sago meal was highly degradable. At 24 h of incubation in the rumen, 90-95% of DM loss was observed. There was a significant interaction between animal species and supplements in the m vivo digestibility of ADF and GE. In animals fed SBM supplement, the in vivo digestibility of ADF was significantly (p<0.05) higher in goats (50.6 ± 4.22%) than in sheep (44.4 ± 3.21%), but digestibility of GE was significantly (p<0.05) higher in sheep (70.2 ± 1.93%) than in goats (63.0 ± 3.07%). The digestibility values of CP and OM were significantly (p<0.05) higher in sheep when compared to goats. Animals fed SBM+SM supplement showed significantly (p<0.05) higher DM and OM digestibility values than animals fed SBM supplement, but digestibility values of CP were significantly (p<0.05) higher in animals fed SBM supplement. Differences in in vivo digestibility values of CF and NDF were not significantly different between animal species or supplements. Water intake, rumen volume (1/kg W0.75), rumen fluid dilution rate and mean retention time were similar between the two animal species. However, rumen fluid dilution rate and mean retention time was significantly (p<0.01) affected by supplements. Animals fed SBM+SM had faster rumen fluid dilution rate and consequently shorter mean retention time.

Indirect measurement of saliva secretion in sheep fed diets of different structures and the effect of such diets on ruminal fluid kinetics and fermentation pattern

Four Suffolk x Dorset sheep were allocated in a 4 x 4 Latin square design and received a hay-barley-molasses diet in one of four different physical structures: (1) pelleted; (2) pelleted:chopped (60:40); (3) chopped:pelleted (60:40); or (4) chopped. The animals were penned individually and the diet was restricted to provide 20 g of dry matter (DM) per kilogram live weight daily. The effects of the diets on rumen fluid kinetics, fermentation pattern and microbial nitrogen (MN) supply were examined. Saliva secretion was estimated using an indirect method based on water balance in the rumen. When the animals were fed the chopped diet, the salivation rate, rumen fluid volume and rumen liquid outflow were all increased significantly (P < 0.05 to P < 0.01). No consistent effect of dietary structure on rumen fluid dilution rate, purine derivative (PD) excretion or MN supply was observed. Dietary structure had no effect on the rumen fermentation pattern, digestibility of DM or nitrogen.

Hay intake, milk production and rumen fermentation in British Saanen goats given concentrates varying widely in protein concentration

AbstractAbout 8 weeks after parturition six multiparous British Saanen goats with permanent rumen fistulas were allocated to three dietary treatments in a random sequence for three successive 30-day periods. The treatments were perennial ryegrass hayad libitumwith 1000 glday of concentrates containing 112 (low-protein, LP), 182 (high-protein, HP) or 255 (very high protein, VHP) g crude protein (CP) per kg dry matter (DM) daily. The CP concentration was increased by substitution of soya-bean meal for cereals. From day 19 of each period, when measurements were made, concentrate allowance was reduced to 850 glday and hay intake was offered at proportionately 0·10 more than consumption in the previous 6 days. Hay intake and milk yield increased linearly with CP in the concentrates, but differences between HP and VHP were small and non-significant. Milk composition was unaffected by the treatments, so yields of milk solids followed the same trends as yields of milk, but these were only significant for solids-not-fat. The digestibility of neutral-detergent fibre, acid-detergent fibre and nitrogen (N) all increased with increasing CP, but significantly so only for N; the digestibility of DM and organic matter was unaffected.The digestibility of the hay incubated in the rumen was unaffected by the treatments. With increasing N intake, faecal, urine and milk N increased linearly as did apparently digested N but N retention did not follow a consistent pattern. Rumen volatile fatty acids and pH were unaffected but concentration of rumen ammonia and blood urea increased with increasing CP as did rumen fluid dilution rate. The results suggest that, with lactating goats given diets of moderate quality grass hay and concentrates containing soya-bean meal, responses to concentrations of CP greater than about 180 g/kg DM in the concentrates or 140 g CP per kg DM in the total diet are likely to be small.

Digestion by sheep of ground and unground dried molassed sugarbeet pulp diets and the effect of partially replacing the beet pulp with barley

SUMMARYA 4 x 4 Latin square design experiment was performed at the Ruminant Research Centre, Cockle Park Farm, University of Newcastle upon Tyne, in 1986 to determine the effect of grinding molassed sugarbeet pulp (MSBP) to varying degrees of fineness on overall apparent digestibility in wether sheep when the product constituted 90% of dry matter intake. A product (designatedS) consisting of the pelleted screenings of unground MSBP was significantly less digestible than the other three products. No significant difference in overall apparent digestibility was observed between unground, coarsely ground and finely ground MSBP prepared from the same batch.In a 4 x 6 randomized block design experiment, mature wethers equipped with rumen, duodenal and ileal cannulae were fed, in two meals, 1000 g concentrates and 100 g chopped hay per day. The concentrates consisted of 820 g mixture of barley and MSBP, 167·5 g soyabean meal, 10 g vitamins and minerals and 2·5 g chromic oxide per kg (fresh weight). The ratio of MSBP: barley was 1:3, 1:1 or 3:1 and the MSBP was either unground or finely ground. The aim was to determine the effect of replacing MSBP with barley on the nature of the rumen fermentation, overall apparent digestibility of the diet and the efficiency of rumen microbial protein synthesis (using 35S as a microbial marker).There were no significant differences between the six diets in overall apparent digestibility of dry matter and organic matter, but N digestibility increased significantly (P &gt; 0·05) as barley replaced MSBP in the diet. As before, the particle size of MSBP had no effect on overall apparent digestibility of the diet. The quantity of microbial N was reduced (nonsignificantly) and the efficiency of rumen microbial protein synthesis decreased (P&gt; 0·05) compared with the other treatments when sheep were fed diets in which the ratio of MSBP: barley was 1:1. The particle size of MSBP had no effect on these factors.As barley replaced MSBP in the diet, the mean pH of rumen fluid, calculated over 24 h, tended to decrease and there was a significant increase (P&gt; 0·05) in the length of time that the rumen fluid was below pH 6. There were no significant differences between treatments in the concentration of ammonia-N in the rumen fluid. The dilution rate of rumen fluid (measured using14C-Cr EDTA and Co EDTA as markers) decreased (P&gt; 0·05) when MSBP replaced barley in the diet, and ground MSBP gave rise to lower (P&gt; 0·05) dilution rates than unground MSBP. There were no significant differences between treatments in the ruminal concentration of total volatile fatty acids (VFAs) or the proportions of individual VFAs.

The Potential of a Phyllosilicate (Palabora Vermiculite) as Buffer in Dairy Cattle Diets

Four rumen-fistulated Holstein cows were used to determine the ability of vermiculite to alter rumen fermentation, rumen fluid dilution rate, milk production, and nutrient utilization in a 4×4 Latin square experiment. Treatments consisted of 1) basal diet (70% concentrate:30% Eragrostis curvula hay), 2) basal + .6% NaHCO3 + 1.8% vermiculite, 3) basal + 1.2% NaHCO3, and 4) basal + 3.6% vermiculite. Feed intake and milk production were not affected, but the NaHCO3 treatments tended to increase milk fat production. The 1.2% NaHCO3 treatment increased rumen pH and fluid dilution rate, decreased molar percent propionate, and increased acetate:propionate ratio. Rumen NH3 N was not affected. Milk yield (kg/d) and milk fat (%) for the treatments were 1) 19.3, 3.33; 2) 19.4, 3.59; 3) 19.8, 3.62; and 4) 18.7, 3.32. Rumen fluid pH, dilution rate (%/h), and acetate: propionate ratio were 1) 5.75, 10.9, 2.08; 2) 5.89, 11.5, 2.16; 3) 5.95, 12.1, 2.38; and 4) 5.80, 11.6 and 1.82. Treatments had little effect on nutrient digestibilities and serum mineral concentrations. Vermiculite did not show any promise as a buffer but NaHCO3 proved to be an effective buffer in diets based on Eragrostis hay and 70% concentrate diets.

Ruminal Degradation and Outflow of Amino Acids in Cows

Two rumen- and duodenum-cannulated cows were used to study the disappearance rate, degradation in, and outflow from the rumen of four amino acids administered individually into the rumen at the following dose levels (mmol): lysine 273-547-820, tyrosine 276-496-828, isoleucine 381-762-1143 methionine 335. Calculations were based on the use of PEG (polyethylene glycol, 4000) as liquid marker for determination of the volume and dilution rate of rumen fluid. At the same dry matter intake a comparison was made between the influence of a high-forage and a low-forage diet. At the lowest dose level, the initial rates of disappearance (mmol/l per h) were 0.52 for lysine, 0.48 for tyrosine, 0.55 for isoleucine and 0.58 for methionine. The rates increased with increasing dose levels. The fractions of administered amino acids flowing out of the rumen and the fractions degraded in the rumen were studied over an 11 h period. At the lowest dose level, outflow (mmol/11 h) amounted to 42 and 54 for lysine, 36 and 29 for tyrosine, 93 and 48 for isoleucine, 104 and 75 for methionine on the high and low forage diet, respectively. The corresponding figures for degradation were 232 and 209, 239 and 247, 287 and 333, 226 and 259 mmol/11 h. The fractions of an administered amino acid flowing intact out of the rumen increased, and the fractions degraded in the rumen decreased, with increasing doses.

Passage Rates, Rumen Fermentation, and Weight Change in Protein Supplemented Grazing Cattle

Protein supplementation is widely used to enhance the nutritional status of cattle on rangeland. The effects of protein supplementation on particulate and fluid passage rates, rumen fermentation, and weight gain were evaluated on cattle grazing dormant blue grama rangeland. Twelve rumen-cannulated steers were randomly allotted to 3 equal supplement groups (Utreatment): cottonseed cake (CSC), pelleted alfalfa (ALF), or no supplement (CON). Supplements were individually fed every other day at isonitrogenous levels (1.7 kg/hd CSC vs 3.6 kg/hd ALF). Particulate passage rate was measured during 2 collection periods. Concurrently, 102 yearling heifers were allotted to the same treatment groups for measurement of average daily gain. Cattle were fed these treatments from January through April 1983. In a second trial, 9 rumen-camudated steers were randomly allotted to the same treatment groups as trial 1. An intraruminal dose of CoEDTA was used to estimate fluid passage rates. Rumen ammonia, volatile fatty acids, and pH were also measured. In trial 1, average daily gain did not differ between ALF and CSC supplemented heifers; however, both ALF and CSC gained more than CON heifers. Passage rate estimates were not different among treatment groups. In trial 2, rumen fluid dilution rate, vohune, and oufflow rate were not different among treatments. Rumen ammonia-N was different at 11 h postsupplementation when the CSC steers had higher levels than steers in other treatment groups. Rumen pH was not influenced by supplementation. Molar proportions of acetate and propionate at 8 and 11 h after supplementation differed among treatment groups. Acetate was lowest in ALF, intermediate in CSC, and highest in CON supplemented steers. Propionate followed the reverse trend. Overall, protein supplementation improved livestock performance but the mechanism involved was not elicited. The current data suggest shifts in fermentation patterns and meeting dietary demands for gain are the factors involved in improving performance.

The passage of protozoa from the reticulo-rumen through the omasum of sheep.

1. Protozoa in rumen contents and omasal effluent of growing wethers were counted. The wethers were equipped with rumen and abomasal cannulas, and omasal sleeves attached to the omasal-abomasal orifice. Rumen fluid dilution rates were elevated by continuous infusions of hypertonic mineral solutions (3-4 litres/d) for 24 d. Rumen contents and omasal effluent were sampled between 9 and 21 h during the last 10 d of each experiment. 2. Protozoal concentrations in omasal effluent were only 0.2-0.3 those found in the rumen under normal conditions. The ratio of protozoal concentrations in rumen: those in omasal effluent was for small Diplodinium spp. 4.6 (SD 0.9), for Ophryoscolex spp. 4.3 (SD 1.0), for Dasytricha ruminantium 4.0 (SD 0.5), for Isotricha spp. 3.8 (SD 0.8), for Entodinium spp. 3.6 (SD 0.9) and for Polyplastron multivesiculatum 2.6 (SD 0.5). 3. Elevation of rumen fluid dilution rate by 20 and 55% respectively, increased protozoal concentrations in omasal effluents from 22 to 33% and from 31 to 47% those in rumen contents. The apparent residence times of protozoa in the rumen were decreased 50% by the infusion of a mineral-salt solution. The increase in rumen fluid dilution rate had no significant effect on concentrations of protozoa in the rumen or on the differences of the apparent residence times between different species. The apparent residence time of holotrichs remained the same before and after infusion of the mineral-salt solution. 4. Apparent residence times of individual species of protozoa in the rumen were, under normal feeding conditions, 2.55 d, and were four to six times longer than the mean residence time of CrEDTA in the rumen.

Digestion of proteins of varying degradability in sheep. 1. Fermentation in and rate of passage from the reticulorumen.

Sugarbeet pulp, citrus pulp, sugarbeet molasses and minerals and vitamins were mixed with different amounts of groundnut expeller, potato protein, peas or dried brewers' grains to give 6 concentrates with protein solubility from 7 to 51%. The concentrates (600 g daily) were given with rye grass (300 g daily) to 2 Texel wethers weighing about 70 kg with a cannula in the dorsal rumen sac. With increasing degradability of protein, rumen fermentation was less stable, the diurnal variation and content of ammonia in rumen fluid were increased, the ratio of non-glucogenic to glucogenic volatile fatty acids decreased and the dilution rate of rumen fluid increased. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Relationship of rumen fluid dilution rate to rumen fermentation and dietary characteristics of beef steers.

Data from seven beef steer trials were compiled and regression analyses used to evaluate relationships among molar proportions of acetate (Ac), propionate (Pr) and butyrate (Bu), total concentration of volatile fatty acids (VFA), rumen ammonia (NH3), rumen pH, rumen fluid dilution rate (FDR), rumen fluid volume (FVOL), body weight (WT), dry matter intake (DMI) and dietary concentration and intake of crude protein (CP and CPI), acid detergent fiber (ADF and ADFI), ash (ASH and ASHI) and metabolizable energy (ME and MEI). Of the six fermentation variables, Pr (negative regression coefficient, beta) and pH (positive beta) were related (P less than .05) to FDR, but only 3 and 12% of the variation in these two variables, respectively, was explained by FDR. When FDR was described by dietary characteristics, ASHI was positively related to FDR (R2 = .16). The best two-variable model for FDR contained DMI (positive beta) and WT (negative beta) and increased R2 to .36. Fluid volume was best described by ME (positive beta; R2 = .20). The two-variable model for FVOL added ASH with a positive partial beta (R2 = .23). When fermentation variables were regressed on dietary characteristics, Ac was best described by ADF (positive beta; R2 = .71). The variable that best described Pr proportion was ADF (negative beta; R2 = .50), and addition of CP (negative beta) and MEI (positive beta) into the Pr model improved R2 to .70. Molar proportion of butyrate was related to CP (positive beta; R2 = .23), and addition of ME (positive beta) to the model improved the R2 to .31. Total VFA concentration was best described by ADFI (positive beta; R2 = .14). An R2 of .29 resulted when ME (positive beta) and CPI (negative beta) were included in the total VFA model. Rumen pH was related to ADF (positive beta; R2 = .45), and addition of CP (positive beta) to the rumen pH model increased R2 to .55. Crude protein concentration was related to ruminal NH3 level (positive beta; R2 = .42), and inclusion of ADFI (positive beta) into the model improved the R2 to .47.

EFFECTS OF SLAFRAMINE ON SALIVARY FLOW AND RUMEN FUNCTION

Consumption of red clover contaminated with slaframine increased salivary flow, and tended to increase rumen fluid dilution rate and acetate to propionate ratio in wethers. Subcutaneous administration of purified slaframine increased eating salivary flow rate up to 316% in steers. Key words: Slaframine, salivary flow, rumen function

Urea synthesis and degradation in sheep given pelleted-grass diets containing flaked barley.

1. Three sheep fitted with rumen and oesophageal cannulas were given hourly the following diets in successive experiments: 1000 g pelleted-grass cubes/d (diet A) and 700 g pelleted-grass cubes plus 300 g flaked barley/d (diet B).2.During the final week of each 4-week dietary regimen, a balance trial was conducted and on separate days each sheep was continuously infused with [14C]urea and NaH14CO3 intravenously and NaH14CO3 intraruminaily. C transfer rates between blood urea, blood bicarbonate and rumen bicarbonate pools were calculated from the specific radioactivity of urea and bicarbonate sampled and isotope infusion rate during each experimental period. In the same period, an oral infusion of 51Cr-EDTA was maintained and salivary flow rate and composition determined from samples collected from the oesophageal fistula.3. The inclusion of flaked barley in the pelleted-grass diet significantly (P &lt; 0·01) increased the apparent digestibility of organic matter (0·069), apparently digestible organic matter intake and nitrogen balance, and increased the efficiency cf dietary N utilization from 0·059 (diet A) to 0·290 (diet B). Increased N balance was the result of a significant (P) &lt; 0·01 reduction in urinary urea excretion.4. The rumen fluid of sheep given diet A had higher pH and bicarbonate concentrations but lower butyric acid concentrations than that of sheep given diet B. There was no significant effect of diet on total volatile fatty-acid or ammonia concentrations in rumen fluid, or on osmolaiity and rumen fluid dilution rate. The irreversible loss of bicarbonate from rumen fluid was markedly increased when flaked barley was included in the diet, with most of the loss occurring directly from rumen fluid.5. Sheep given diet A had higher salivary secretion rates (18·8 l/d) than those given diet B (12·7 l/d), and with the exception of urea, there was no effect of diet on the concentrations of total N, protein N, alpha;-amino-N, uric acid-N or bicarbonate in saliva. Urea concentrations in saliva were significantly correlated (r20·64) with blood urea concentrations, but not with salivary flow rate. Salivary secretions contributed 2·2 and 1·4 gN/d to the rumen of sheep given diets A and B respectively, with urea forming only 45–33% of the total N secreted.6. When flaked barley was included in the pelleted-grass diet, there was a significant (P &lt; 0·01) decrease in urea synthesis rate (diet A 20·0 g N/d, diet B 9·7 g N/d), a significant increase in amount (diet A 2·3 g N/d. diet B 3·0 g N/d) and proportion (diet A 0·024, diet B 0·57) of recycled urea degraded in the rumen. The permeability of the rumen wall to urea was also significantly increased in sheep given the flaked barley diet (diet A 1·35 g N/d, diet B 2·45 g N/d).7. A model of urea metabolism in sheep given each diet is described, and the mechanisms by which flaked barley inclusion increased urea recycling to the rumen and the efficiency of dietary N utilization are discussed.

Effects of Intraruminal Infusions of Mineral Salts on Volatile Fatty Acid Production in Steers Fed High-Grain and High-Roughage Diets

Four rumen fistulated Holstein steers were used to assess the effects of intraruminal salt infusions on various rumen characteristics including volatile fatty acid production rates. In the first experiment, the basal diet consisted of 75% concentrate and 25% corn silage (high-grain diet). The experimental design was a 4×4 Latin square in which the four treatments were: 1) intraruminal infusion of 8 liters of water (control) or 8 liters of water plus 2) 288g sodium bicarbonate, 3) 200g sodium chloride, or 4) 600g sodium chloride. In the second experiment, procedures were the same except the basal diet consisted of 64% alfalfa hay and 18% each of corn silage and concentrate (high-roughage diet). When the high-grain basal diet was fed, intraruminal infusions of mineral salts increased dilution rate of rumen fluid. Total fluid flow from the rumen also was increased by salt infusions with sodium bicarbonate and the most sodium chloride (600 g/day) exerting greatest effects for both dietary regimens. Salt infusions reduced the molar percentage of rumen propionate and increased the molar percentage of acetate when the high-grain diet was fed. These same treatments were without effect on molar percentages of rumen acids when the high-roughage diet was fed. The change in the molar percentages of acetate and propionate on the high-grain ration was solely from reduction in propionate production. The lower production of propionate, from salt infusions, may have occurred because of the washout of readily fermentable materials. Dry matter disappearance from feeds placed in dacron bags and suspended in the rumen was unaffected by infusion of mineral salts.

EFFECT OF DIETARY CONCENTRATE LEVEL ON RUMEN FLUID DILUTION RATE

Rumen fermentation, and rumen fluid dilution rate as influenced by 75% (75C) or 25% (25C) concentrate diets fed at the same level of energy intake was studied with four steers. Rumen pH was lower (P &lt; 0.05) in steers fed 75C. Liquid flow rate and liquid turnover time were increased (P &lt; 0.05) by feeding 25C. Key words: Liquid dilution rate, fermentation, concentrate level

Rumen Volatile Fatty Acid Production and Nutrient Utilization in Steers Fed a Diet Supplemented with Sodium Bicarbonate and Monensin

Effects of feeding dietary supplements of monensin and sodium bicarbonate singly or in combination on production of rumen volatile fatty acids, nitrogen balance, and rumen water kinetics were studied. Four rumen fistulated steers were fed a diet (50% concentrate mix and 50% corn silage) ad libitum in a 4×4 Latin square design (21-day periods) with a 2×2 factorial arrangement of treatments.Sodium bicarbonate increased feed intake, water intake, rumen pH, fluid dilution rate, and decreased both molar proportion and production rate of propionate in the rumen. Alteration of the ratio of acetate to propionate reflects the large decrease in propionate production relative to the small increase in acetate production. In contrast, monensin did not alter significantly rumen fluid dilution rate or ruminal pH but did decrease the molar proportion of acetate and increase that of propionate. Monensin increased production of both acetate and propionate in the rumen; however, the large increase in propionate production appears to account for more of the increase in molar proportion of propionate in the rumen. Increases in total volatile fatty acid production per kilogram of dry matter consumed with monensin supplementation appears to result from decrease in feed intake, thereby increasing ruminal retention time of dry matter and potentially the extent of digestion. Efficiency of nitrogen utilization was not altered by either sodium bicarbonate or monensin.

Alteration of Rumen Fermentation, Milk Fat Synthesis, and Nutrient Utilization with Mineral Salts in Dairy Cows

The ability of mineral salts to alter rumen fermentation, rumen fluid dilution rate, milk fat synthesis, and nutrient utilization was investigated in dairy cows fed a high-concentrate, milk-fat depressing diet. Four rumen-fistulated Holstein cows were in a 4×4 Latin square design. Treatments consisted of: 1) basal (25% corn silage: 75% concentrate on a dry matter basis), 2) basal + 2.0% sodium chloride, 3) basal + 2.0% sodium bicarbonate, and 4) basal + 2.4% limestone. Addition of limestone to the basal diet reduced dry matter intake but increased efficiency of dietary nutrient utilization for milk synthesis. Sodium bicarbonate increased synthesis of milk fat. Sodium chloride also tended to increase milk fat synthesis whereas limestone had no effect. Milk yields (kg/day) and milk fat (%) for the four treatments were 1) 29.5, 2.40; 2) 29.3, 2.66; 3) 28.9, 3.26;and 4) 29.2, 2.32. Rumen fluid pH, dilution rate (%/hour), and molar percentage of acetate and propionate were: 1) 5.98, 10.3, 49 and 39; 2) 6.02, 12.4, 55 and 32; 3) 6.16, 12.2, 58 and 25; and 4) 5.92, 10.7, 51 and 38. Limestone was totally ineffective in altering ruminal pH, fluid dilution rate, molar percentages of acetate and propionate, and synthesis of milk fat. Improved feed efficiency for milk production after addition of limestone was related to an increase in starch digestion compared to the basal ration (95 versus 88%).

Quantitative studies of food protein degradation and the energetic efficiency of microbial protein synthesis in the rumen of sheep given chopped lucerne and rolled barley.

1. In a randomized block design, four sheep were given 800 g daily of diets containing: chopped lucerne (L), chopped lucerne-rolled barley (2:1; LB), rolled barley-chopped lucerne (2:1; BL), rolled barley (B); each diet was supplemented with minerals, vitamins and urea as considered necessary. Chronic oxide was included in the diets as a flow marker. 2. Flows of organic matter (OM) and non-ammonia-nitrogen (NAN) to the small intestine (SI) were measured and microbial protein was identified by a 35S-incorporation procedure. 3. OM disappearance in the rumen increased linearly with increasing inclusion of barley in the diet but there was no significant change in microbial NAN flow to the SI so that the yield of microbial NAN (g)/kg fermented OM (FOM) decreased from 29.6 (diet L) to 22.7 (diet B). Changes in the energetic efficiency of microbial protein synthesis appeared to be unrelated to alterations in rumen fluid volatile fatty acid (VFA) proportions or in rumen fluid dilution rate (D). 4. The degradability of dietary protein (non-urea-N), estimated using the 35S procedure, was 0.72, 0.76, 0.86 and 0.86 for diets L, LB, BL and B respectively. Similar values were obtained from concurrent polyester-bag experiments when the fractional outflow rate of undegraded protein from the rumen (k) was assumed to be 0.046.