Influences of dietary sucrose and urea on transfer of endogenous urea to the rumen of sheep and numbers of epithelial bacteria

Nutritional performance and metabolic characteristics of cattle fed tropical forages with protein and starch supplementation

Effects of protein supplementation, with and without starch supplementation, on nutritional performance and metabolic characteristics of cattle fed low- and medium-quality tropical forages were evaluated using 4 cannulated steers distributed according to a 4 × 4 Latin square. Experimental periods were divided into two subperiods. In the first subperiod, two animals received low-quality hay and two animals received medium-quality. Supplementation schemes were evaluated in the second subperiod: low-quality hay with protein (300 g of crude protein - CP/d); low-quality hay with protein (300 g CP/d) and starch (225 g/d); medium-quality hay with protein (300 g CP/d); and medium-quality hay with protein (300 g CP/d) and starch (225 g/d) supplementation. Without supplementation, medium-quality forage provided higher intake, digestibility, nitrogen balance (NB) and efficiency of nitrogen utilization (EFNU). Comparing subperiods, supply of supplements depressed medium-quality forage intake, but did not affect low-quality forage intake. Supplementation increased NB, EFNU and serum concentration of IGF1 in animals fed low-quality forage. Protein supplementation increases nitrogen retention in animals, an effect attributed mainly to anabolic stimuli. However, this effect is more prominent when animals are fed low-quality forages. No positive impact on animal metabolism was obtained with combination of supplemental protein and starch.

Nitrogen utilization, whole-body urea-nitrogen kinetics, omasal nutrient flow, and production performance in dairy cows fed lactose as a partial replacement for barley starch

The objective of this study was to determine whether the partial replacement of barley starch with lactose (fed as dried whey permeate; DWP) affects N utilization, whole-body urea kinetics, and production in dairy cows. Eight lactating Holstein cows were used in a replicated 4 × 4 Latin square design with 28-d periods. Four cows in one Latin square were ruminally cannulated and used to determine dietary effects on whole-body urea kinetics and N utilization. Cows were fed a barley-based diet that contained 3.6% (dry matter basis) total sugar (TSG; designated control), or diets that contained 6.6, 9.6, or 12.6% TSG. Dietary TSG content was increased by the replacement of barley grain with DWP (83% lactose). Diets were isonitrogenous (∼17.3% crude protein), and starch contents of the control, 6.6, 9.6, and 12.6% TSG diets were 24.3, 22.2, 21.2, and 19.1%, respectively. Whole-body urea kinetics were measured using 4-d infusions of [¹⁵N¹⁵N]-urea with concurrent total collections of feces and urine. Dry matter intake (mean = 26.7 kg/d), milk yield (mean = 34.9 kg/d), and milk protein and fat contents were unaffected by diet. Ruminal ammonia-N concentration decreased linearly as TSG content increased, whereas ruminal butyrate concentration increased linearly as TSG content increased. Urinary excretion of total N and urea-N changed quadratically, whereas urinary excretion of total N (% of N intake) tended to change quadratically as TSG content increased. Fecal N excretion linearly increased as TSG content increased. A quadratic response was observed for total N excretion as TSG content increased. Milk N and retained N were not affected by diet. As TSG content increased, we observed quadratic responses in the omasal flow of fluid-associated and total bacterial nonammonia N, endogenous production of urea-N, urea-N recycled to the gastrointestinal tract, and urea-N returned to the ornithine cycle. Dietary TSG content did not affect the anabolic utilization of recycled urea-N or the proportion of recycled urea-N that was used for bacterial growth. Our results indicate that feeding DWP did not influence dry matter intake, milk yield, or milk composition. Feeding DWP decreased ruminal ammonia-N concentration, but this did not result in positive responses in milk protein secretion or N balance. The quadratic response in omasal flow of total bacterial nonammonia N indicated that including TSG beyond 9.6% of diet dry matter might depress ruminal microbial protein synthesis.

Nitrogen recycling and feed efficiency of cattle fed protein-restricted diets

The ability of cattle to grow and reproduce when ingesting low-protein diets is a crucial attribute for productive beef cattle systems in the seasonally dry tropics and subtropics. Nitrogen (N) recycling to the rumen is an important and known physiological mechanism allowing ruminants to efficiently grow in low-protein diets, but is usually disregarded in the nutritional models. This review discusses the role and magnitude of N recycling to provide additional N as microbial substrate in the rumen and in determining the efficiency of ruminants ingesting low-protein diets, to better understand the major factors regulating N recycling to the rumen. In addition to a review of the literature, study-adjusted regressions were used to evaluate various aspects of crude protein (CP) intake and availability, N recycling and excretion. There is large variation in N excretion and N-use efficiency among diets and among individuals, illustrating the opportunity for improvement in overall efficiency of cattle production. These data indicated that N recycling to the entire gastrointestinal tract supplies from half to twice as much N available for microbial growth as does the diet. Addition of rumen-degradable protein can increase rumen efficiency in using the available energy, as, conversely, the addition of fermentable energy can increase rumen efficiency in using the available CP. The present review has demonstrated that both are possible because of greater N recycling. Also, the importance of preserving the available N for determining individual variation in feed efficiency and the implications for selection are discussed. Nitrogen recycling can be controlled at both the epithelial wall of compartments of the gastrointestinal tract and at the liver, where ureagenesis occurs. Addition of fermentable energy can increase N recycling to the rumen and to post-ruminal tract by acting at both sites, and the mechanisms for this are discussed in the text. Although the effect of altering CP concentration in the diet has been substantially investigated, other factors potentially modulating N recycling, such as total fermentable energy, sources of protein and energy, hormonal modulation, and genetic variance, remain poorly understood. The selection of more efficient animals and development of diets with a lower environmental impact inescapably means further elucidation of the N-recycling mechanism.

Effects of Supplements with Different Protein Contents on Nutritional Performance of Grazing Cattle During the Rainy Season

The objective of this study was to evaluate the effects of supplements with different crude protein (CP) contents on grazing cattle intake, digestibility, ruminal fermentation pattern, and nitrogen (N) metabolism characteristics during the rainy season. Five ruminal and abomasal cannulated Holstein×Zebu steers (296 kg body weight, BW) were used in a 5×5 Latin square design. The animals grazed five signal grass paddocks (0.34 ha). The five treatments evaluated were: Control (no supplement) and 1.0 g of supplement/kg BW with 0, 330, 660, and 1,000 g of CP/kg as-fed. The supplement was composed of starch, soybean meal, urea, and ammonium sulphate. There was a positive linear effect (p≤0.033) of the CP content in the supplements on the organic matter (OM), CP, and digested OM intakes. The provision of supplements did not increase (p≥0.158), on average, total and ruminal digestibilities of OM and CP. However, the increase in CP content in the supplements caused a positive linear effect (p≤0.018) on ruminal digestibilities of OM and CP. Additionally, a quadratic effect of the CP contents of the supplements were observed (p = 0.041) for the ruminal digestibility of neutral detergent fiber corrected for ash and protein, with the highest estimate obtained with the CP content of 670 g/kg. The supply of supplements increased (p<0.001) the ruminal ammonia N concentration, which also changed linearly and positively (p<0.001) according to increase in CP content in the supplements. The apparent N balance and relative N balance (g/g N intake) were not, on average, changed (p≥0.164) by the supplements supply. However, both showed a tendency of a linear increase (p≤0.099) with increasing supplement CP content. The supplements increased (p = 0.007) microbial N production in the rumen, which also changed linearly and positively (p = 0.016) with increasing supplement CP content. In conclusion, protein supplementation in grazing cattle during the rainy season, while stimulating voluntary forage intake, results in higher efficiency of N utilization when compared to energy supplementation. This is a possible response to increased microbial protein synthesis in the rumen and improved N status in the animal body.

Urea-N recycling in lactating dairy cows fed diets with 2 different levels of dietary crude protein and starch with or without monensin

Rumensin (monensin; Elanco Animal Health, Greenfield, IN) has been shown to reduce ammonia production and microbial populations in vitro; thus, it would be assumed to reduce ruminal ammonia production and subsequent urea production and consequently affect urea recycling. The objective of this experiment was to determine the effects of 2 levels of dietary crude protein (CP) and 2 levels of starch, with and without Rumensin on urea-N recycling in lactating dairy cattle. Twelve lactating Holstein dairy cows (107 ± 21 d in milk, 647 kg ± 37 kg of body weight) were fed diets characterized as having high (16.7%) or low (15.3%) CP with or without Rumensin, while dietary starch levels (23 vs. 29%) were varied between 2 feeding periods with at least 7d of adaptation between measurements. Cows assigned to high or low protein and to Rumensin or no Rumensin remained on those treatments to avoid carryover effects. The diets consisted of approximately 40% corn silage, 20% alfalfa hay, and 40% concentrate mix specific to the treatment diets, with 0.5 kg of wheat straw added to the high starch diets to enhance effective fiber intake. The diets were formulated using Cornell Net Carbohydrate and Protein System (version 6.1), and the low-protein diets were formulated to be deficient for rumen ammonia to create conditions that should enhance the demand for urea recycling. The high-protein diets were formulated to be positive for both rumen ammonia and metabolizable protein. Rumen fluid, urine, feces, and milk samples were collected before and after a 72-h continuous jugular infusion of (15)N(15)N-urea. Total urine and feces were collected during the urea infusions for N balance measurements. Milk yield and dry matter intake were improved in cows fed the higher level of dietary CP and by Rumensin. Ruminal ammonia and milk and plasma urea nitrogen concentrations corresponded to dietary CP concentration. As has been shown in vitro, Rumensin reduced rumen ammonia concentration by approximately 23% but did not affect urea entry rate or gastrointestinal entry rate. Urea entry rate averaged approximately 57% of total N intake for cattle with and without Rumensin, and gastrointestinal rate was similar at 43 and 42% of N intake for cattle fed and not fed Rumensin, respectively. The cattle fed the high-protein diet had a 25% increase in urea entry rate and no effect of starch level was observed for any recycling parameters. Contrary to our hypothesis, Rumensin did not alter urea production and recycling.

The influence of oscillating dietary protein concentrations on finishing cattle. I. Feedlot performance and odorous compound production1,2

We hypothesized that oscillation of the dietary CP concentration, which may improve N retention of finishing beef steers, would reduce production of manure odor compounds and total N inputs while yielding comparable performance. Charolais-sired steers (n = 144; 303 +/- 5 kg of initial BW) were used in a completely randomized block design (6 pens/treatment). The steers were fed to 567 kg of BW on the following finishing diets, which were based on dry-rolled corn: 1) low (9.1% CP), 2) medium (11.8% CP), 3) high (14.9% CP), or 4) low and high oscillated on a 48-h interval for each feed (oscillating). Steers fed low tended (P = 0.08) to have less DMI (7.80 kg/d) than steers fed medium (8.60 kg/d) or oscillating (8.67 kg/d), but not less than steers fed high (8.12 kg/d). Daily N intake was greatest (P < 0.01) for steers fed high (189 g), intermediate for medium (160 g) and oscillating (164 g), and least for low (113 g). The ADG was lower (P < 0.01) for steers fed low (1.03 kg) than for those fed medium (1.45 kg), high (1.45 kg), or oscillating (1.43 kg). Similarly, steers fed low had a lower adjusted fat thickness (P < 0.01) and yield grade (P = 0.05) and tended (P = 0.10) to have less marbling than steers fed the other 3 diets. In slurries with feces, urine, soil, and water, incubated for 35 d, nonsoluble CP was similar among slurries from steers fed medium, high, or oscillating, but was less (P < 0.01) in slurries from steers fed low. However, throughout the incubation period, slurries from steers fed high or oscillating had greater (P < 0.01) concentrations of total aromatics and ammonia than those from steers fed low or medium. Also, the slurries from steers fed oscillating had greater (P < 0.01) concentrations of branched-chain VFA than manure slurries from steers fed any of the other diets. These data indicate that although there is no apparent alteration in the performance of finishing steers fed diets with oscillation of the dietary protein, there may be undesirable increases in the production of compounds associated with malodor.

Net portal and hepatic flux of nutrients in growing wethers fed high-concentrate diets with oscillating protein concentrations

We hypothesized that oscillating dietary CP would improve N retention by increasing the uptake of endogenous urea N by portal drained viscera (PDV), compared with static dietary CP regimens. Chronic indwelling catheters were surgically implanted in the abdominal aorta, a mesenteric vein, a hepatic vein, and the portal vein of 18 growing Dorset x Suffolk wethers (44.6 +/- 3.6 kg of BW). Wethers had ad libitum access to the following diets in a completely randomized block design: 1) Low (9.9% CP), 2) Medium (12.5% CP), or 3) Low and High (14.2% CP) diets oscillated on a 48-h interval (Osc). Dry matter intake was greater (P = 0.04) for the Osc diet (1,313 g/d) than the Low diet (987 g/d) and was intermediate for the Medium diet (1,112 g/d). Nitrogen intake was not different between the wethers fed the Osc (25.4 g/d) and Medium diets (22.2 g/d), but was lower (P < 0.01) in wethers fed the Low diet (16.0 g/d). Wethers fed the Osc diet (6.7 g/d) retained more (P < 0.04) N than did those fed the Medium diet (4.0 g/d). Hepatic arterial blood flow was not different (P = 0.81) between wethers fed the Osc (31 L/h) or Medium diet (39 L/h) but was greater (P = 0.05) in wethers fed the Low diet (66 L/h). Net release of alpha-amino N by the PDV did not differ (P = 0.90) between the Low (37.8 mmol/h) and Medium diets (41.5 mmol/h) or between the Osc (53.0 mmol/h) and Medium diets (P = 0.29). Net PDV release of ammonia N was less (P = 0.05) for the Low diet than for the Medium diet, and this was accompanied by a similar decrease (P = 0.04) in hepatic ammonia N uptake. Urea N concentrations tended to be (P = 0.06) less in arterial, portal, and hepatic blood in wethers fed the Low diet compared with those fed the Medium diet. Wethers fed the Osc diet tended (P = 0.06) to have a greater PDV uptake of urea N than did those fed the Medium diet, but there was no difference between the Osc and Medium diets (P = 0.72) in hepatic urea N release. Net PDV uptake of glutamine tended to be greater (P < 0.07) in wethers fed the Low diet (6.7 mmol/h) than those fed the Medium diet (2.7 mmol/h). These data indicate that oscillating dietary protein may improve N retention by increasing endogenous urea N uptake by the gastrointestinal tract.

Form of rumen-degradable carbohydrate and nitrogen on microbial protein synthesis and protein efficiency of dairy cows

Sixteen multiparous lactating Holstein cows (four with rumen cannulae) were fed diets varying in the content and form of ruminally degradable carbohydrates and N to examine dietary effects on microbial protein synthesis (MPS) and whole animal N efficiency, and to evaluate the use of a model based on milk urea N (MUN) for predicting urinary N excretion and N utilization efficiency (NUE). A replicated Latin square design (consisting of diet and experimental period) was employed. The four diets consisted of two low protein diets with either 20% ground corn (diet LP) or 13.5% ground corn plus 3% sucrose (diet LP sucrose) and two high protein diets with 13.5% corn and 3% sucrose with either urea (diet HP urea) or soybean meal (diet HP SBM) as supplemental rumen-degradable protein sources. The intakes of dry matter and N were increased by increasing dietary crude protein (CP) level. However, the yields of milk and milk protein were not affected by CP level. Yield of microbial protein was reduced by sucrose and increased by CP level. There were no differences between urea and SBM supplementation on DM intake, milk yield, or MPS. Mean urinary N excretion for all cows (252 g/d) was underestimated by 55 g/d or overestimated by 25 or 33 g/d using alternative equations based on MUN. Subsequently, NUE (mean = 22.4%) was underestimated by 7.5, 3.2, or 2.9%, using a previously published set of equations. Urinary N excretion and NUE could be predicted within 10 and 14% of observed values, respectively, using a set of equations incorporating MUN. Therefore, MUN appears to be a useful tool to help assess N losses from lactating cows.

Nitrogen metabolism by the microbial flora of the rabbit caecum

The dense microbial flora of the rabbit caecum consisted chiefly of bacteria (10(11)/g) with small numbers of yeast cells (10(6)/g). Using strictly anaerobic technique, 23% of the direct microscopic cell count was cultivated and 55% of the cultivatable bacteria utilized ammonia as the sole source of nitrogen. Ureolytic bacteria were isolated from the caecal lumen and mucosa and were identified as Bacteroides vulgatus, Clostridium clostridiiforme, Bacillus spp. and Staphylococcus spp. Ammonia assimilation by the bacterial flora of the caecum was by incorporation into alpha-oxoglutarate catalysed by NADPH-linked glutamate dehydrogenase.

Isolation and identification of adherent epimural bacteria during succession in young lambs

Successive changes in aerobic and anaerobic bacterial counts and changes in the generic composition of the epimural community in lambs from 1 to 10 weeks were determined. Bacterial culture counts revealed a predominantly anaerobic community, with the mean anaerobic count being 1.4 X 10(7) CFU/cm2 of tissue surface. The aerobic count was highest at 1 week of age and declined significantly thereafter to a mean of 1.8 X 10(4) CFU/cm2, thus representing only 0.13% of the mean anaerobic count after week 1. Of the 345 strains isolated anaerobically at 1, 2, 4, 6, 8, and 10 weeks of age, 47, 32, 12, 32, 2, and 5% were capable of growth in a partially reduced medium, indicating a reduction in the number of facultative anaerobes with time. The majority of isolated strains were identified as belonging to genera commonly isolated from rumen contents. In some instances, however, strains did not correspond to previously described species, and some genera were present in proportions different from those expected in rumen fluid. At three of the sampling times, one genus was dominant, constituting 45 to 55% of the isolates. These dominant isolates were Streptococcus bovis, Bacteroides sp., and an anaerobic Streptococcus sp. for weeks 1, 2, and 10, respectively. During the transition period (weeks 4 to 8), two or more groups were codominant.

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

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.

Microbial ecology and activities in the rumen: part 1

This review describes the progress which has been made during the last 10 to 15 years in the field of rumen microbiology. It is basically an account of new discoveries in the bacteriology, protozoology, biochemistry, and ecology of the rumen microbial population. As such it covers a wide range of subjects including the isolation and properties of methanogenic bacteria, the role of rumen phycomycete fungi, anaerobic energy conservation, and general metabolic aspects of rumen microorganisms. It also attempts, however, to describe and develop new concepts in rumen microbiology. These consist principally of interactions of the microbemicrobe, microbe-food and microbe-host types, and represent the main areas of recent advance in our understanding of the rumen ecosystem. The development of experimental techniques such as chemostat culture and scanning electron microscopy are shown to have been instrumental in progress in these areas. The paper is concluded with an assessment of our present knowledge of the rumen fermentation, based on the degree of success of experiments with gnotobiotic ruminants inoculated with defined flora and in mathematical modeling of the fermentation. The efficacy of chemical manipulation of the fermentation in ruminant is also discussed in this light.