Organic Matter Flow Research Articles

Rumen fermentation and nutrient digestion in cattle fed diets varying in forage and energy source

Four Holstein steers, each fitted with a rumen fistula and duodenal t-shaped cannula, were used in a 4 × 4 Latin square design to measure the rumen fermentation and digestibility of the following diets: (1) alfalfa hay and barley; (2) alfalfa hay and ground corn; (3) corn silage and barley; (4) corn silage and corn. All diets contained 50% forage and 50% concentrate on a dry matter (DM) basis, with a minimum of 10% of the DM as alfalfa hay. Diets based on alfalfa hay had more organic matter digestion in the rumen and total digestive tract than those containing corn silage. Diets containing corn as the major concentrate energy source had less ruminal starch digestion and a greater flow of organic matter to the duodenum than diets containing barley. Total tract digestion of nitrogen (N) was greater for barley than corn diets, but was similar between forage sources. Neither the forage nor concentrate energy source affected bacterial protein synthesis. Rumen pH was higher and ammonia-N was lower in alfalfa than barley diets. In addition, rumen acetate was higher and rumen propionate was lower, resulting in a greater acetate-to-propionate ratio in alfalfa diets.

Digestion of complex carbohydrates and large bowel fermentation in rats fed on raw and cooked peas (Pisum sativum).

Rats were fed on four semi-purified diets in which raw or cooked peas (Pisum sativum var. Sentinel) provided 250 or 500 g/kg diet. Pressure-cooking of peas followed by rapid freezing and freeze-drying increased the proportion of starch resistant to alpha-amylase (EC 3.2.1.1) without previous treatment with dimethyl sulphoxide. There were only minor effects of cooking on the digestibilities of non-starch polysaccharides and their constituent sugars. With the higher dietary pea concentration there were marked increases in the flow of organic matter to, and fermentation in, the large bowel. These increases were associated with significant increases in colonic tissue and contents weights, and in colonic transit time. Both cooking and dietary pea inclusion rate altered the pattern of volatile fatty acids in caecal contents and in portal blood.

Stream Fish Ecology: A Landscape Perspective

M ore than 40 years ago, conservationist Aldo Leopold articulated the need for a ethic, or self-imposed limitation on the degree to which a person will modify the landscape, to protect overall ecosystem quality (Leopold 1949). Since Leopold made that plea, land use has continued to be a primary factor causing the decline of fishery resources in stream ecosystems (Karr et al. 1985, Salo and Cundy 1987). The pervasiveness of degradation of these resources indicates that most land-use decisions have been made with little understanding or regard for their effect on adjacent and more distant components of the landscape. Landscape ecology (Forman and Godron 1986) offers new opportunities for improving understanding of landscape dynamics and strengthening decisions regarding the influence of land-use disturbances on fishery resources. Landscape ecology focuses on three interrelated characteristics of the environment: structural relationships among landscape elements; functional interactions among these elements, including the flow of water, organic matter, nutrients, and species; and natural and anthropogenic changes in structural and functional relationships of landscape elements over time. In this article, I briefly review the basic life cycle of stream fish and the

The influence of lasalocid and cationomycin on nitrogen digestion in sheep: Comparison of methods for estimating microbial nitrogen

An in vivo study was carried out to evaluate the effect of a new ionophore (cationomycin) on nitrogen digestion compared with lasalocid. Three diets based on forage were given (a control diet, a "cationomycin" diet, a "lasalocid" diet) to six sheep fitted with rumen duodenal and ileal cannulae over three different periods in a Latin square design experiment. The supply of lasalocid or cationomycin (33 mg kg−1) decreased (P < 0.05) the breakdown of dietary proteins in the rumen and lowered the microbial protein synthesis whatever the microbial marker used (diaminopimelic acid or purine bases). The duodenal and ileal flows of organic matter (OM), ammonia nitrogen (NH3-N), nonammonia nitrogen, and amino acids (AA) were not affected by the ionophore addition. We could not use the AA profile method to estimate the microbial contribution to the duodenal flow of nonammonia nitrogen because of the strong similarities in AA composition of the feed and the rumen microbial sample. The efficiency of microbial synthesis was significantly (P < 0.05) decreased by cationomycin, and tended to decrease with lasalocid. Only lasalocid increased the digestibility of dietary nitrogen in all the digestive tract. Key words: Ionophore, lasalocid, cationomycin, digestion, nitrogen, sheep, rumen

Mercury in swedish forest soils and waters — Assessment of critical load

As a result of air pollution, the content of Hg in fish has significantly increased in a large part of Scandinavia and North America. In this paper, the occurence and fluxes of Hg in Swedish forest soils and waters are reviewed and synthesized. The main objective is to describe and evaluate the present transport of anthropogenic Hg from atmospheric deposition, through the terrestrial compartment and running waters to lake basins and also to comprehend the main factors influencing these fluxes. The transportation and distribution. of Hg in forest soils and waters is closely related to the flow of organic matter. The content of Hg in humic matter is higher in southern and central areas compared to the north of the country. Compared to background concentrations, the Hg content has increased in the southern and central part by about a factor of 4–7, while the overall increase in the north is by about a factor of 2 to 3. The increased content of Hg in forest soils may have an effect on organisms and biological processes in the soil. Regarding budget calculations for whole catchment areas and for the mor layer of the soil, a reduction of about 80% from present atmospheric wet deposition must be obtained to reach “critical load” with respect to conditions in Scandinavia.

Seasonal variation in the interactions between piscivorous fish, planktivorous fish and zooplankton in a shallow eutrophic lake

The interactions between the higher trophic levels in a shallow eutrophic lake were studied during the course of a year. Three fish species determined the main pathways of organic matter flow within the system: the predominantly planktivorous bream (Abramis brama), the obligate planktivorous smelt (Osmerus eperlanus), and the piscivorous pikeperch (Stizostedion lucioperca). Of the thirteen common zooplankton taxa Daphnia hyalina and cyclopoid copepods were utilized most by the planktivorous fish, while the large production of small cladocerans is almost left unutilized. The seasonal variations of production and consumption are large. This is mainly affected by seasonal variation of the water temperature. The production of O + smelt is efficiently utilized by the pikeperch. Being the most important zooplankton consumer, as well as the most important prey group, O + fish plays a key role in the Tjeukemeer food web.

Primary productivity and particulate organic matter flow in an estuarine mangrove-wetland in Hong Kong

Net primary productivity and organic matter flow of a mangrove-dominated wetland was estimated by following production and detritus dynamics in a tidal pond in north west Hong Kong in 1986–1988 (9.1 ha). Total productivity was 12.47 t dry wt ha−1 yr−1, of which >90% was from emergent macrophytes (the mangroveKandelia candel and the reedPhragmites communis). High turbidity and high summer temperatures probably limited respective production by phytoplankton and benthic macroalgae (dominated byEnteromorpha crinata). Despite the high total productivity, little detritus was exported from the emergent macrophyte stands, due to the low inundation frequency. This created a net water column carbon deficit which was provided for by the high organic matter import (mean = 4.42 g ash free dry wt m−2 d−1) from the incoming water. This same sediment and particulate organic carbon input giving a high accretion rate of 1.7 cm yr−1 was probably also the force behind progressive dis-coupling of emergent macrophyte production from water column consumers. This resulted in a tendency to retain production in the emergent macrophyte stands while the water column community increasingly relied on allochthonous carbon. This shift from a net exporter to a net importer of carbon in landward wetlands is probably characteristic of the transition into nutrient-conservative terrestrial systems.

Effect of supplementary crude protein level and degradability in grass silage-based diets on performance of dairy cows, and digestibility and abomasal nitrogen flow in sheep

ABSTRACTFour concentrate supplements differing in crude protein (CP) and undegradable protein (UDP) content were offered to 16 lactating Friesian cows together with grass silage (dry matter (DM) 196 g/kg, pH 4·38, CP 160 g/kg DM, in vitro DM digestibility 0·68)ad libitumin a Latin-square trial with 3-week periods. The supplement treatments were: (1) barley 122 g CP per kg DM, degradability (dg) 0·77; (2) barley/soya-bean meal 210 g CP per kg DM, dg 0·69; (3) barley/soya-bean meal/fish meal 190 g CP per kg DM, dg 0·61; (4) barley/soya-bean meal/fish meal 219 g CP per kg DM, dg 0·59. Supplements were given at 8 kg/day. Total daily intakes of silage (kg DM), CP and UDP (g) on treatments 1 to 4 were 7·77, 2087, 375; 8·35, 2804, 655; 8·29, 2676, 717; 8·70, 2917, 826, respectively. Milk yield (kg/day) and yields of fat, protein and lactose (g/day) on the four treatments were 21·3, 791, 617, 984; 23·0, 816, 688, 1055; 23·0, 818, 696, 1050; 23·6, 813, 735, 1071 for treatments 1 to 4 respectively. Yield and concentration of protein and lactose were significantly lower on treatment 1 than on the other treatments, while the of blood metabolites indicated treatment effects on blood glucose, non-esterified fatty acids, plasma protein and urea. Digestibility of organic matter and non-ammonia nitrogen (NAN) flow to the abomasum (g/day), measured in sheep given a fixed silage/supplement ratio at maintenance, were 0·81 and 18·4, 0·81 and 20·8, 0·82 and 21·4, 0·82 and 22·4 for treatments 1 to 4 respectively. The NAN flow was significantly greater on treatment 4 than on treatment 1.

Effects of a fat and ground maize supplement on feed intake and digestion by cattle consuming bermudagrass hay ( Cynodon dactylon)

Five beef cows (450 kg) and five Holstein steers (254 kg) were used in two Latin square experiments to determine the effects on intake and digestion of supplementing bermudagrass ( Cynodon dactylon) hay with maize and fat, singly and in combination, and to compare fat poured on hay with fat mixed with maize. The cows received hay at 1.0% of their body weight (BW) per day alone (control) or with ground maize (0.49% BW) and/or fat (0.054% BW, beef tallow). Treatments were control (C), maize alone (MZ), fat poured on hay alone (PF), maize plus poured fat (MZ-PF) and maize mixed with fat (MZ-MF). Calcium carbonate (0.011% BW) was given to all supplemented animals. Mean ruminal fluid protozoal counts were higher with than without supplements ( P < 0.05), for MZ than for PF, and for simultaneous vs. singular offering of maize and fat ( P < 0.05). Flows of microbial organic matter and nitrogen at the duodenum were higher with than without supplements, for MZ than for PF, and for MZ-MF than for MZ-PF. Digestion of neutral detergent fiber in the whole tract declined with supplementation, but differences among supplement treatments were not significant. In the second study, steers received hay ad libitum and higher levels of supplements (maize 0.89, fat 0.099 and calcium carbonate 0.021% BW day −1). Total dry matter intake was C 5.86, MZ 7.86, PF 6.83, MZ-PF 7.90 and MZ-MF 7.75 kg day −1, being affected by supplementation and higher for MZ than PF ( P < 0.05). Total tract neutral detergent fiber digestion was C 72.0, MZ 67.0, PF 69.2, MZ-PF 65.1, and MZ-MF 61.0%, and was depressed by supplementation and lower for simultaneous vs. singular supplementation with maize and fat ( P < 0.05). In conclusion, there were no advantages in intake or digestion to adding fat to supplemental maize either separately or mixed as compared with supplementation with maize alone.

Influence of Synchronizing Protein and Starch Degradation in the Rumen on Nutrient Utilization and Microbial Protein Synthesis

A 4 × 4 Latin square design with four multiparous cows in midlactation fitted with duodenal cannulae was used to determine the effect of synchronization of protein and starch degradation in the rumen on nutrient availability in lactating cows. As major starch and protein sources, diets contained: barley plus cottonseed meal; barley plus brewers dried grains; milo plus cottonseed meal; and milo plus brewers dried grains. Experimental periods were 12 d and consisted of 8 d adjustment and 4 d collection. Chromium oxide was used as the marker to determine digestibility and nutrient flow from the rumen. Microbial protein synthesis was estimated from nucleic acid content in duodenal samples. Apparent and corrected rumen digestibilities of DM, organic matter, CP, and starch were higher for diets containing barley than milo but were not affected by protein source. For diets containing barley and milo, starch digested postruminally averaged 820 and 2190 g/d and percentage digestibility was 70 and 77%. No difference among diets was found in DM, organic matter, and CP flow to the small intestine; however, microbial N synthesis was higher in diets containing barley than in diets containing milo.

THE APPARENT DIGESTIBILITIES OF DRY MATTER, ORGANIC MATTER AND NONAMMONIA NITROGEN IN THE FORESTOMACH, SMALL INTESTINE, AND LARGE INTESTINE OF WETHERS EXPOSED TO A COLD ENVIRONMENT

Eight shorn yearling Suffolk wethers cannulated in the rumen, abomasum, and terminal ileum were exposed to temperatures of 0 to + 2 °C or 21–25 °C in a crossover experiment to determine effects on the apparent digestibilities of dry matter (DM), organic matter (OM) and nonammonia nitrogen (NAN) in the forestomach and small intestine. Animals were housed in metabolic crates and fed 1600 g d−1 chopped bromegrass hay. After 30 d acclimation, feed, ruminal, abomasal, terminal ileal and fecal samples were acquired for the determination of DM, OM, cell wall constituents (CWC), acid detergent fiber (ADF) and NAN. Rumen volatile fatty acid composition was also determined. Digesta flows at the abomasum and terminal ileum were estimated from the dilution of 103ruthenium-phenanthroline and 51chromium-EDTA during continuous infusion of these markers into the rumen. Dry matter (P &lt; 0.10), OM (P &lt; 0.05) and NAN (P &lt; 0.05) flows to the abomasum were increased during cold exposure. The apparent digestibilities of DM (P &lt; 0.10), OM (P &lt; 0.05) and NAN (P &lt; 0.05) in the rumen were decreased during cold exposure but the apparent digestibilities of these components did not change in the small intestine. Consequently, during cold exposure the proportion of OM and NAN digested in the small intestine relative to OM digested in the entire gastrointestinal tract was increased. Total ruminal VF A concentration was not affected by temperature; however, the molar proportion of acetate declined (P &lt; 0.05) and that of propionate increased (P &lt; 0.01). This, together with a greater proportion of the digestion taking place in the small intestine, may improve the efficiency of utilization of metabolizable energy and partly compensate for the decreased ruminal digestion of OM during cold exposure. Key words: Organic matter, nitrogen, digestion, sheep, cold environment

The intake and utilization of urea-treated rice straw by sheep differing in body condition

Prior to the experiment two groups of 10 sheep were fed to either gain (group F) or lose (group T) weight. At the beginning of the experiment group F sheep weighed on average 57.7 kg fleece-free liveweight (W) and had a total body fat (TBF) content of 154 kg, while group T sheep weighed 42.6 kg and had a TBF content of 9.7 kg. During the experiment all sheep were given a urea-treated rice straw-based diet ad libitum for 56 days with an intra-ruminal infusion of urea and sodium sulfate. Measurements were made of feed intake and digestibility and of the amounts and composition of digesta in the reticula-rumen (ReRu) and flowing through the abomasum.Group T sheep consumed more feed (dry matter intake 1 170 v. 1040 g day-1, 24.9 v. 19.1 g kg W-1) and spent more time chewing (16.5 v. 14.1 h day-1) than group F sheep. There were no differences in the digestibility of dietary constituents.Associated with the greater feed intakes by group T sheep were increased amounts of total digesta (8.59 v 7.67 kg) and of dry matter (DM) (1040 v. 960 g), organic matter (OM) (820 v. 750 g) and neutral detergent fibre (NDF) (690 v. 620 g) in the ReRu. Flows of total digesta (22.45 v. 18.64 kg day-1), DM (910 v. 800 g day-1), OM (600 v. 510 g day-1) and NDF (330 v. 270 g day-1) through the abomasum were also greater in group T sheep. However, there were no differences between treatments in the proportion of digestion which occurred in the ReRu, in the fractional digestion rate of NDF in the ReRu or in the fractional passage rate of NDF from the ReRu.Group T sheep generally maintained weight (-4 g day-1) throughout the experiment and their TBF only declined from 9.7 to 9.1 kg. In contrast, group F sheep lost weight at 74 g day-1 and TBF declined from 15.8 to 14.1 kg.It is concluded that removal of limitations of essential nutrients enabled sheep in poor condition to consume more of this straw-based diet than those in good condition.

The digestion of perennial ryegrass (Lolium perenne cv. Melle) and white clover (Trifolium repens cv. Blanca) by grazing cattle.

1. Pure swards of perennial ryegrass (Lolium perenne cv. Melle) as a primary growth (May), trimmed primary growth (early June) and regrowth (late June), and white clover (Trifolium repens cv. Blanca) as a mature primary growth (July) and vegetative regrowth (August), were grazed by twelve Friesian steers (mean body-weights throughout experiment 152-231 kg) at daily allocation rates of forage which provided dry matter (DM) intakes ranging from 28 to 36 g/kg body-weight). 2. Total nitrogen contents of the three ryegrasses declined with season (37-20 g/kg DM), but in vitro organic matter (OM) digestibilities were relatively constant (0.76-0.79). The clovers had higher N (average 36.6 g/kg DM) and lower fibre and water-soluble carbohydrate contents than the grasses, and in vitro OM digestibilities of 0.70 and 0.76 respectively. 3. Duodenal digesta samples were obtained, using a portable sampling apparatus from the animals grazing the pasture, and estimates of the flow of nutrients into the small intestine were derived using two indigestible markers which were continuously infused into the rumen using a portable infusion apparatus. Forage intakes were calculated from estimates of faecal output of indigestible OM and the predicted in vivo OM digestibilities of the forages consumed. Coefficients of variation for OM flow to the small intestine and OM intake were 11.8 and 10.9% respectively. 4. The apparent digestion of OM in the rumen ranged from 722 to 741 g/kg digestible OM intake and from 681 to 711 g/kg digestible OM intake for the grass and clover diets respectively. Substantial losses of ingested N before the small intestine were measured on all diets except the regrowth ryegrass. Losses were 0.30 and 0.40 g/g N intake on the primary growth ryegrass and the regrowth clover respectively; N contents were 37 and 39 g/kg DM respectively. 5. Comparison of the values obtained at pasture with that obtained when similar diets were offered to housed cattle (Beever et al. 1985) indicated that combined relations relating duodenal OM and non-ammonia-N (NAN) flows to OM and N intakes respectively could be established for each diet. For two diets (primary-growth grass and regrowth clover) the relations were curvilinear; for the remaining diets, the derived relations were linear.(ABSTRACT TRUNCATED AT 400 WORDS)

EFFECT OF AMOUNT AND LENGTH OF ALFALFA HAY IN DIETS CONTAINING BARLEY OR CORN ON SITE OF DIGESTION AND RUMEN MICROBIAL PROTEIN SYNTHESIS IN DAIRY COWS

Eight lactating Holstein cows fitted with simple cannulae in the rumen and proximal duodenum were used in a 2 × 2 × 2 factorial experiment in a randomized complete block design. The factors studied were: (1) forage length (full bloom alfalfa hay, long or chopped); (2) forage level in the total ration (25 or 75%); and (3) type of grain in the concentrate mixes (barley or corn). Organic matter (OM) intake was not affected by level of forage or grain type but was greater (P &lt; 0.05) with chopped hay than with long hay. Apparent total digestion of OM increased (P &lt; 0.01) from 59.7 to 68.1% as forage in the diet decreased from 75 to 25%, but site of digestion was unaffected. Flow to the duodenum of nonammonia-N, feed N, and microbial N were unaffected by forage level, forage length, or grain type. No differences in main effects were observed between corn and barley but interactions between grain type and forage length or amount indicate that type of grain had an influence upon site of OM digestion and flow of nonammonia-N and microbial N from the rumen. Efficiency of microbial protein synthesis (MPS) was positively associated with turnover rate of rumen solids regardless of liquid dilution rate. When no change in turnover rate of solids occurred, efficiency of microbial protein synthesis increased in association with increases in turnover rate of liquid. Key words: Lactation, cattle, bacteria, alfalfa, duodenum, rumen

Sulfur, carbon, and nitrogen isotopes used to trace organic matter flow in the salt‐marsh estuaries of Sapelo Island, Georgia1

The stable isotopes of sulfur, nitrogen, and carbon were used to trace organic matter flow in salt marshes and estuarine waters at Sapelo Island, Georgia. Organic matter inputs from terrestrial sources as detrital input either from forests adjacent to the marshes or from rivers were not detectable by their isotopic signatures in estuarine consumers. The results suggest that there are two major sources of organic matter for the fauna of the marshes and estuarine waters of Sapelo Island: Spartina and algae. The long‐standing debate about the relative importance of Spartina detritus and algae in supporting marsh and estuarine secondary production appears from this analysis to be a draw; both sources are important and their relative importance is determined by feeding mode, size, location, and trophic position of the marsh and estuarine consumers.

The effects of frequency of feeding on some quantitative aspects of digestion in the rumens of growing steers.

Three steers with simple rumen and abomasal cannulas were given ground and pelleted diets containing predominantly dried grass meal (DG) or rolled barley (RB). Diets were given at frequencies of two or eight feeds/d in a simple changeover design. Chromic oxide and polyethylene glycol were given as flow markers and flows (g/24 h) of organic matter (OM), nitrogenous and carbohydrate compounds were calculated. Ribonucleic acid and 35S were used as microbial markers and diaminopimelic acid (DAP) as a bacterial marker. Frequency of feeding had no significant effect on mean rumen pH, ammonia levels or liquid outflow rates with either diet. Rumen volume was decreased and abomasal digesta flow increased on Diet DG with more feeds but these parameters were unaffected with Diet RB. Increased feeding frequency with both feeds resulted in increased numbers of protozoa. There were no significant effects of feeding frequency of Diet DG on the abomasal flows of any of the nitrogenous constituents measured. However, there was a significant increase in microbial-N flow from 33 to 43 g/d with more frequent feeding of diet RB which was not reflected in bacterial-N flow as measured by DAP. The apparent digestion of OM in the rumen, expressed as g/g intake with diet DG was 0.41 and 0.31 for two feeds and eight feeds/d respectively. Corresponding values for diet RB were 0.56 and 0.63 respectively. The reduction in OM digestion with frequent feeding of diet DG was reflected in similarly reduced rumen digestibilities of all dietary carbohydrate components whereas the increase in OM digestion with diet RB was reflected only by the component sugars of the dietary fibre. The efficiencies of microbial protein synthesis (expressed as gMN/kg ADOM) increased from 36 to 46 when the feeding frequency of diet DG was increased from two to eight times/d. No significant effect of frequency of feeding was found for diet RB. Mouth to abomasum degradation of feed-N (expressed as g/g intake) of 0.64 was unaffected by the number of feeds of diet DG but was significantly increased from 0.55 to 0.82 when eight rather than two feeds/d of diet RB were given.

Effects of dietary forage proportion on digestive function in maintenance-fed beef cows. Fescue and bermudagrass hays.

Five crossbred beef cows (Hereford x Angus, 428 kg), cannulated in the rumen and duodenum, were used in a Latin square experiment to determine the effects of dietary proportions of fescue (F) and bermudagrass (B) hays (0:1, .25: .75, .5:.5, .75: .25 and 1:0) on digestive function. Feed intake was 85% of ad libitum intake of F alone (1.04% of body weight). Fescue contained 1.19% nitrogen (N), 74.8% neutral detergent fibre (NDF) and 6.3% acid detergent lignin (ADL), and B contained 1.99% N, 84.5% NDF and 6.1% ADL. Ruminal ammonia-N decreased and four- and five-carbon fatty acid concentrations increased linearly (P less than .05) with increasing F. Mean particle size of duodenal digesta was not affected by F level, but specific gravity of duodenal particles changed quadratically (P less than .05) as F rose, being greatest with 25 and 50% F. Ruminal fluid volume was constant, but dilution rate increased linearly (P less than .05) as F increased. Passage rate of B was faster than that of F in mixed diets. Organic matter (OM) flow and digestibilities, true ruminal N disappearance and microbial efficiency were not affected (P greater than .10) by F. True ruminal N disappearance and microbial efficiency were not affected (P greater than .10) by F. True ruminal N disappearance ranged from 73 to 78%, and microbial growth efficiency was between 18 and 22 g microbial N/kg OM fermented. Ruminal digestibilities of NDF, acid detergent fibre (ADF), cellulose and hemicellulose decreased linearly (P less than .05) as F increased, being 68.2, 64.9, 65.6, 61.2 and 61.6% for NDF, 58.9, 54.7, 56.2, 53.3 and 53.2% for ADF, 64.7, 61.3, 62.1, 59.0 and 59.1% for cellulose, and 76.1, 74.4, 75.4, 70.1 and 72.2% for hemicellulose for 0, 25, 50, 75 and 100% F, respectively. Digestive function in beef cows fed mixed F-B diets at a low level of intake related directly to dietary forage proportions and digestive characteristics when forages were fed alone.

Effects of supplements on intake, rumen function and nutrient supply and growth in cattle eating alkali-treated oat straw

1. Expt 1. Six 200 kg Hereford heifers fitted with rumen and abomasal cannulas were fed ad lib. on alkali-treated oat straw sprayed with urea and minerals, with no supplement (O), or 700 g rolled barley (B) or cottonseed meal (C)/d, in a 3 x 3 Latin square with two replicates. 2. Intakes of the basal diet were not significantly affected by the supplements. Intakes of digestible organic matter (OM) were 3135, 3325 and 3515 g/d on diets O, B and C respectively. Abomasal OM flow on diet C was 13 and 12% higher than on diets O and B respectively (P less than 0.05) which was associated with a decrease in the proportion of OM intake apparently digested in the rumen (P less than 0.05) and an increase in the proportion of abomasal OM digested in the lower gut (P less than 0.05). 3. Total nitrogen and bacterial N flows at the abomasum were significantly higher (P less than 0.01 and P less than 0.05 respectively) on diet C than on diets O and B. Efficiency of bacterial N synthesis on diet C was 19 and 28% higher than on diets O and B respectively (P less than 0.05). 4. Dry matter (DM) pool size in the rumen was greater on diet C than on diets O and B (P less than 0.05). 5. Expt 2. Thirty-three 210 kg Friesian heifers were allocated to the same treatments as in Expt 1. Intakes of the basal straw diet were not significantly affected by the supplements.(ABSTRACT TRUNCATED AT 250 WORDS)

Sulfur and Carbon Isotopes as Tracers of Salt-Marsh Organic Matter Flow

Stable isotopes of sulfur and carbon were used to trace the dominant flows of organic matter from producers to macroconsumers in Great Sippewissett Salt Marsh on Cape Cod. Spartina alterniflora and sulfur-oxidizing bacteria were found to assimilate isotopically light sulfides produced via sulfate reduction, and this light sulfur was detected in consumers. In contrast, phytoplankton and upland plants assimilate isotopically heavier SO42- with little or no fractionation. A dual-isotope approach using both 613C and 634S showed that Ilyanassa obsoleta and Fundulus heteroclitus depend very heavily on Spartina detritus, while filter feeders such as Crassostrea virginica and Geukensia demissa depend on a mixture of plankton and Spartina detritus. Spartina detritus and plankton were both shown to be much more important as organic matter sources for marsh macroconsumers than either sulfur-oxidizing bacteria or organic matter derived from terrestrial inputs.

Effect of forage species and season on nutrient digestion and supply in grazing cattle.

1. A total of twenty Friesian steers were grazed on pure swards of either perennial ryegrass (Lolium perenne cv. Melle) or white clover (Trifolium repens cv. Blanca) from May to late August to examine the effect of forage species and season on nutrient digestion and supply. Within each forage species, two daily allowances of forage (i.e. 30 and 60 g dry matter (DM)/kg live weight) were given, and nutrient flow into the small intestine was measured on thirteen separate occasions (viz. seven grasses and six clovers). 2. Total nitrogen content of the grasses varied between 28 (early season), 19 (mid-) and 33 (late) g/kg DM, whilst the clovers showed a much narrower range and all values were higher (39-45 g/kg DM). In vitro organic matter (OM) digestibilities of plucked samples ranged from 742 to 809 g/kg OM (grass) and 712 to 790 g/kg OM (clover), the lowest values being noted in late June (grass) and mid-July (clover). 3. OM intakes calculated from estimated faecal OM output (using unlabelled ruthenium) and predicted OM digestibility of the consumed forage indicated mean values of 20.9 (grass) and 26.0 (clover) g/kg live weight (P less than 0.001), whilst the higher forage allowances increased OM intake by approximately 8% on both grass and clover (P less than 0.01) compared with the low allowance. OM intake was significantly (P less than 0.01) lower on the two primary growths of grass examined in May (mean 16.8 g/kg live weight) than the other five grass diets. 4. Rumen molar propionate levels declined with season but were at all times higher on the grass than on the clover diets, whilst acetate levels were unaffected by forage species. Apart from the late-season grass, mean rumen ammonia concentration was less than 100 mg NH3-N/l on all grass diets, whilst values on the clover diets ranged from 200-350 mg/l. 5. Daily duodenal OM flows in relation to animal live weight were approximately 20% higher on the clover than on the grass diets (grass 9.2, clover 11.2 g/kg live weight, P less than 0.001), but estimates of the proportion of digestible OM apparently digested in the rumen were not significantly influenced by forage species (grass 0.69, clover 0.71).(ABSTRACT TRUNCATED AT 250 WORDS)