Nutrient Excretion Research Articles

Nitrogen and Phosphorus Retention and Excretion in Late-Gestation Dairy Heifers

The objectives of this study were to evaluate the effects of limit feeding diets containing concentrates or by-products in place of forages on manure and nutrient excretion in growing, gravid heifers. Eighteen Holstein heifers confirmed pregnant were grouped by due date and fed 1 of 3 diets (n=6 per treatment) for the last 14wk of pregnancy. Diets were high forage, fed ad libitum (HF); by-product based (BP), fed at the same rate as HF-fed heifers; or low forage (LF), fed at 86% of the HF diet. Diets were designed to supply equal quantities of P, N, and metabolizable energy. Total collection of feces and urine was conducted in wk 14, 10, 6, and 2 prepartum. The HF ration was 90.7% forage, 13.7% crude protein (CP), and contained orchardgrass hay, corn silage, corn grain, soybean meal 44%, and a vitamin-mineral premix. The BP diet was 46.2% forage and 14.0% CP, with 70% of the grain mix space replaced with soybean hulls and cottonseed hulls in a 1:1 ratio, with intake limited to 93% of the dry matter intake (DMI) of HF. The LF ration was 45.3% forage and 17.8% CP, with intake limited to 86% of the DMI of HF. The effect of diet was analyzed with repeated measures, using preplanned contrasts to compare HF with BP and LF with HF and BP. As designed, heifers fed HF and BP had greater DMI than the heifers limit-fed LF, and there was no effect of diet on average daily gain or BW. Intake and digestibility of N were lower, and fecal N excretion was higher, in heifers fed HF and BP than heifers fed LF. Mean feces excretion on both a wet and dry basis was greater for HF heifers compared with BP heifers and less for LF heifers than for HF and BP heifers. Despite differences in urinary output, diet had no effect on urea N excretion, but there was a trend for heifers fed HF and BP rations to excrete less urinary N compared with those fed LF. Compared with HF and BP heifers, LF heifers tended to have lower fecal P excretion and had higher urinary P excretion. Measured manure and urine excretion from heifers fed LF was greater than current American Society of Agricultural and Biological Engineers values, whereas heifers fed HF excreted less manure and urine than predicted. Heifers achieving similar rates of gain from diets differing in forage, grain, and by-product content excreted widely varying quantities of manure.

"Biomoléculas": cellular metabolism didactic software

"Biomoléculas" is a software that deals with topics such as the digestion, cellular metabolism and excretion of nutrients. It is a pleasant, simple and didactic guide, made by and for students. In this program, each biomolecule (carbohydrates, lipids and proteins) is accompanied until its degradation and assimilation by crossing and interrelating the different metabolic channels to finally show the destination of the different metabolites formed and the way in which these are excreted. It is used at present as a teaching-learning process tool by the chair of Physiology and Biophysics at the Facultad de Ingeniería - Universidad Nacional de Entre Ríos.

Ontogeny, diet shifts, and nutrient stoichiometry in fish

Most stoichiometric models do not consider the importance of ontogenetic changes in body nutrient composition and excretion rates. We quantified ontogenetic variation in stoichiometry and diet in gizzard shad, Dorosoma cepedianum, an omnivorous fish with a pronounced ontogenetic diet shift; and zebrafish, Danio rerio, grown in the lab with a constant diet. In both species, body stoichiometry varied considerably along the life cycle. Larval gizzard shad and zebrafish had higher molar C:P and N:P ratios than larger fish. Variation in body nutrient ratios was driven mainly by body P, which increased with size. Gizzard shad body calcium content was highly correlated with P content, indicating that ontogenetic P variation is associated with bone formation. Similar trends in body stoichiometry of zebrafish, grown under constant diet in the laboratory, suggest that ontogeny (e.g. bone formation) and not diet shift is the main factor affecting fish body stoichiometry in larval and juvenile stages. The N:P ratio of nutrient excretion also varied ontogenetically in gizzard shad, but the decline from larvae to juveniles appears to be largely associated with variation in the N:P of alternative food resources (zooplankton vs detritus) rather than by fish body N:P. Furthermore, the N:P ratio of larval gizzard shad excretion appears to be driven more by the N:P ratio at which individuals allocate nutrients to growth, more so than static body N:P, further illustrating the need to consider ontogenetic variation. Our results thus show that fish exhibit considerable ontogenetic variation in body stoichiometry, driven by an inherent increase in the relative allocation of P to bones, whereas ontogenetic variation in excretion N:P ratio of gizzard shad is driven more by variation in food N:P than by body N:P.

Ontogeny, diet shifts, and nutrient stoichiometry in fish

Most stoichiometric models do not consider the importance of ontogenetic changes in body nutrient composition and excretion rates. We quantified ontogenetic variation in stoichiometry and diet in gizzard shad, Dorosoma cepedianum, an omnivorous fish with a pronounced ontogenetic diet shift; and zebrafish, Danio rerio, grown in the lab with a constant diet. In both species, body stoichiometry varied considerably along the life cycle. Larval gizzard shad and zebrafish had higher molar C:P and N:P ratios than larger fish. Variation in body nutrient ratios was driven mainly by body P, which increased with size. Gizzard shad body calcium content was highly correlated with P content, indicating that ontogenetic P variation is associated with bone formation. Similar trends in body stoichiometry of zebrafish, grown under constant diet in the laboratory, suggest that ontogeny (e.g. bone formation) and not diet shift is the main factor affecting fish body stoichiometry in larval and juvenile stages. The N:P ratio of nutrient excretion also varied ontogenetically in gizzard shad, but the decline from larvae to juveniles appears to be largely associated with variation in the N:P of alternative food resources (zooplankton vs detritus) rather than by fish body N:P. Furthermore, the N:P ratio of larval gizzard shad excretion appears to be driven more by the N:P ratio at which individuals allocate nutrients to growth, more so than static body N:P, further illustrating the need to consider ontogenetic variation. Our results thus show that fish exhibit considerable ontogenetic variation in body stoichiometry, driven by an inherent increase in the relative allocation of P to bones, whereas ontogenetic variation in excretion N:P ratio of gizzard shad is driven more by variation in food N:P than by body N:P.

Food Science Education Publications and Websites

Many food science and nutrition departments at colleges and universities have developed tools for assessing student learning. Below are 2 web-accessible assessment resources found as a result of a simple Internet search. Iowa State Univ. Dept. of Food Science and Human Nutrition. Learner Outcomes Assessment Portfolio. http://www.fshn.hs.iastate.edu/outcomes/homepage.php (accessed 8/29/2007) Utah State Univ. Nutrition & Food Sciences. Assessment Plan. http://www.nfs.usu.edu/academics/assessment/assessment.html (accessed 8/29/2007) In future columns I would like to include web links to assessment tools created by academic food science and nutrition departments. If your department has an assessment tool available online, please e-mail me and I will include it in my next column. As always, we welcome your comments and resources. Material should be submitted to: Jim Bird, Science & Engineering Center, Fogler Library, Univ. of Maine, Orono, ME 04469 or e-mail to Jim.Bird@umit.maine.edu. If e-mailing, please put “JFSE submission” in the subject line. The authors note the need for trained nanotechnology professionals in the areas of food and agriculture research. During the second week of the course AGR 101- Introduction to the School of Agriculture and Purdue Univ., students were introduced to the field of nanotechnology in two 50- minute seminars. Students also took an online attendance quiz at the end of each seminar, each including 3 questions on nanotechnology. A small percentage of students took advantage of 2 “Nanotechnology in Action” tours that included hands-on demonstration stations. A pre- and post-survey was administered to students in the course. Of the 514 students taking the course, 335 student surveys were analyzed. The results showed that this exposure to nanotechnology information led to an increase in student awareness of the subject. A detailed analysis of the results is presented. The authors review 46 food safety and hygiene training studies, presenting study results in a series of 4 detailed tables. Summarized are food hygiene training evaluation studies using the following designs: Descriptive, audit, before-after, and comparative-experimentalist. This review is extensive, citing 101 references and with the recent publication date, readers will have an up-to-date literature review on this subject. Using the Delphi method the authors gathered food system education topics from nutrition educators. Using this information, a questionnaire was developed to assess attitudes of high school students on topics such as farmland protection, organic agriculture, hunger, and locally-produced foods. The reliability and validity of the attitude measures are discussed. The authors note that: “The challenge for nutrition educators who choose to engage in food system education is to first understand the complex interconnections among food production, processing, distribution, retail, and consumption, and then to devise creative ways to communicate about that complexity to a young audience.” (p. 95). The professional master of science degree program in food safety offered online for adult learners at Michigan State Univ. is described in detail including background on the establishment of the program, challenges, and curriculum. An overview of the first 3 years of the program, including student demographics, is presented. Information on the program can be found at: http://www.foodsafe.msu.edu/proms/ (accessed 8/22/2007). This paper describes the results of field testing of Baylor College of Medicine Food and Fitness unit, part of the series From Outer Space to Inner Space for middle school children. The unit tested had 6 activities: Energy for life, energy sources, your energy needs, do you fit? you are what you eat, and eating for life. The results of the field test showed “…the unit does…improve students' knowledge of concepts related to energy and nutrition, as measured by the pre/post student assessment.” (p. 789). Descriptions of the unit and the teacher's guide can be found at Baylor College of Medicine Center for Educational Outreach: http://www.ccitonline.org/ceo/content.cfm?menu_id=147 (assessed 8/22/2007). Based on the results of a survey sent to 8 Australian universities (7 respondents), the authors list 15 core elements that should be part of a university nutritional sciences program. Examples of core elements included food standards and regulation; assessment of nutritional status; and absorption, transport, storage, and excretion of nutrients. The benchmarking portion of the survey was responded to by 4 universities and identified good and outstanding practices in scholarly teaching of nutritional science. One indicator of outstanding practice found to be consistent among respondents was “...the integration of teaching with research.” (p. 7). The author describes a classroom demonstration on biochemistry principles of fruit and vegetable spoilage to teach scientific inquiry and reasoning skills. Catalase activity, proteases, and metabolic pathways are discussed in relation to the ripening of fruit and vegetables.

Manure Nutrient Excretion by Lactating Cows Fed Exogenous Phytase and Cellulase

The effect of an exogenous phytase and cellulase-containing enzyme formulation on nutrient digestibility and excretion was evaluated in 24 Holstein cows. Cows were fed corn silage- and alfalfa silage-based diets with or without a cellulase-phytase blend for 31 d in a continuous random design. Treatment groups were balanced for parity, days in milk, and mature-equivalent projected milk yield. Diets contained 37% forage, 18.3% crude protein, 35.4% neutral detergent fiber, 18% acid detergent fiber, and 0.42% P (no supplemental P). Cows were fed once daily in Calan doors and milked 2 times daily. Body weight and milk yield were recorded at each milking. Milk samples were collected on d 28 to 31 at 8 consecutive milkings. On d 28 to 31, fecal grab samples were collected every 8h, with sampling times advanced by 2h each day. Feces samples were pooled by cow. Feed and feces samples were analyzed for acid detergent lignin (used as an internal marker) and for N, P, neutral detergent fiber, and acid detergent fiber. Days in milk were similar between treatments, and body weight and milk yield were unaffected by treatment. Cows fed the enzyme formulation had reduced fecal dry matter, neutral detergent fiber, and acid detergent fiber excretion and reduced fecal excretion of N and P. Apparent digestibility of dry matter, acid detergent fiber, neutral detergent fiber, and N tended to increase with the enzyme formulation. Addition of an exogenous phytase and cellulase enzyme formulation to diets for lactating cows reduced fecal nutrient excretion.

Land use controls nutrient excretion by stream invertebrates along a gradient of agriculture

We examined the relationship between land use in the watershed and nutrient release by mayflies in streams in southcentral Ontario (Canada). Mayfly excretion rates and molar ratios of dissolved organic C (DOC), NH4+, and soluble reactive P (SRP) were measured in 6 streams flowing through watersheds with contrasting agricultural land use. Mass-specific release rates of NH4+ and SRP by mayflies and % agricultural land use (% agriculture) in the watershed were strongly positively related (r2 = 0.48, p < 0.01 and r2 = 0.58, p < 0.05, respectively). Changes in excretion rates and ratios probably were caused by lower periphyton C:N and C:P ratios associated with elevated total dissolved N and total P concentrations (r2= 0.30, p < 0.05 and r2= 0.38, p < 0.001, respectively) in streams in watersheds with high % agriculture. Mayfly mass-specific excretion rates and periphyton elemental composition were related to % agriculture, but the relatively constant body C, N, and P content in mayflies across all streams suggests strong homeostasis in these consumers. Watershed land use alters nutrient loading, which influences periphyton elemental composition and, ultimately, stoichiometry of nutrient fluxes through invertebrate consumers.

Cornell Net Carbohydrate and Protein System: A model for precision feeding of dairy cattle

The Cornell Net Carbohydrate and Protein System (CNCPS) predicts cattle requirements and nutrient supply for site-specific situations. This paper describes the CNCPS version 6 (CNCPSv6), which represents a re-engineering and updating of CNCPS version 5 with the following objectives: (1) improve the organization of the model and user interface to improve speed and accuracy in formulating diets for a herd of dairy cattle, (2) expand the carbohydrate pools to include sugars, soluble fibers, and organic and volatile fatty acids, (3) integrate a fat model to account for ruminal lypolization and biohydrogenation, and absorption of fatty acids in the small intestine, and (4) update the computational sub-models with new information. The CNCPSv6 model was re-designed using object-oriented programming in which physiological functions ( e.g. growth, lactation, pregnancy) and anatomical compartments ( e.g. rumen, intestines) were programmed as objects. The interface uses farm, location, and group flow, which decreases the number of inputs required per cattle group and allows for more rapid evaluation of diets, feed requirements, and nutrient excretion by location, group, and herd. The revised implementation of the body reserves sub-model allows accounting for fluxes in energy reserves when formulating diets. Updated equations and coefficients include the prediction of rumen ammonia balance and feed passage rates, indigestible DM, MP lactation efficiency, and DMI. The CNCPSv6 was evaluated with data from individually fed lactating dairy cows from three independent studies. As implemented, CNCPSv6 accounted for a similar proportion of the variation (86%) in first limiting (ME or MP) milk production as CNCPSv5 but with a lower bias (1% versus 4%, respectively). We concluded the re-designing and updating of the CNCPS improved its ability to formulate and evaluate a feeding program for a herd of dairy cattle with greater accuracy and efficiency.

The Effects of Dietary Chicory and Reduced Nutrient Diets on Composition and Odor of Stored Swine Manure

<h2>ABSTRACT</h2> Two experiments were conducted to examine the impact of dietary chicory on growth performance and odor of stored swine manure. In Exp. 1, 180 nursery pigs (10.6 ± 2kg BW) were used in a 21-d experiment to evaluate the effects of replacing corn with chicory (0.5 to 10.0%) on pig performance. Overall, ADG increased (linear; P < 0.02) and ADFI tended to increase (P < 0.10) as the level of chicory increased in the diet. This effect was primarily due to numerically reduced performance when pigs were fed 0.5 or 1.0% chicory, with growth similar for pigs fed 0, 5, or 10%. In Exp. 2, 12 barrows (initially 59 ± 3kg BW) were fed each of 4 experimental diets during four 10-d periods in a replicated 4 × 4 Latin square design to compare nutrient excretion and odor analysis of pigs fed 1) conventional corn-soybean meal diet; 2) diet formulated to minimize nutrient excretion; 3) diet 1 with 10% chicory; and 4) diet 2 with 10% chicory. Feces and urine were collected and measured for N, S, and P excretion and retention, as well as for odor and gas analyses. Pigs fed diets formulated to reduce nutrient excretion had less (P < 0.001) total N and P excretion and had simulated slurry with reduced (P < 0.001) pH and less (P < 0.001) S, N, and ammonia. The addition of chicory to the diet also reduced (P < 0.03) N and P excretion. In conclusion, chicory can be fed to pigs to reduce nutrient excretion while maintaining growth performance.

Improved Colostomy Technique and Excrement (Urine) Collection Device for Broilers and Broiler Breeder Hens

In conducting nutritional experiments using chickens, scientists are limited in determining the urinary excretion of nutrients because of the difficulty of separating urine from feces. Our main objective was to improve the colostomy procedure for urine collection in broilers and both urine and egg collection for broiler breeder hens. Ketamine HCl (10 to 30 mg/kg i.m.) in combination with Xylazine (2 to 6 mg/kg i.m.) was used to anesthetize broilers (4 wk old) and broiler breeder hens (25 wk old). The colostomy technique involved: 1) transecting the distal colon at approximately 1.5 to 2 cm from the proximal cloaca and ligating the distal colonic segment with 3-0 absorbable surgical suture, 2) ligating the seromuscular coat of the colon to the peritoneal tissue at 3 points in a triangular shape using 4-0 silk suture, 3) ligating the mesentery at the skin level to prevent continued bleeding of the colostomy stoma, and 4) placing 3 sutures using a triangulation technique that consisted of the seromuscular aspect of the transected proximal colonic segment and the skin, and finally, 5) suturing all exteriorized edges of the transected proximal colonic segment after mucosal eversion to the skin with simple interrupted sutures using absorbable suture. For the purpose of urine or egg collection or both, the appropriate size of drainable pouch with a curved tail closure was used. Feces were collected on a tray. The colostomized broilers could be kept for several days and the colostomized broiler breeder hens for several months to collect urine, eggs (for breeder hens), and feces separately without the problem of cross-contamination.

Nutrient Digestibility and Mass Balance in Laying Hens Fed a Commercial or Acidifying Diet

The objectives of the current study were to evaluate the effect of an acidifying diet (gypsum) combined with zeolite and slightly reduced crude protein (R) vs. a control diet (C) on nutrient retention in laying hens and compare 3 approaches to estimating nutrient excretion from hens: 1) mass balance calculation (feed nutrients − egg nutrient), 2) use of an indigestible marker with analyzed feed and excreta nutrient content, and 3) an environmental chamber that allowed for capturing all excreted and volatilized nutrients. Hens (n = 640) were allocated randomly to 8 environmental chambers for 3-wk periods. Excreta samples were collected at the end of each trial to estimate apparent retention of N, S, P, and Ca. No diet effects on apparent retention of N were observed (53.44%, P > 0.05). Apparent retention of S, P, and Ca decreased in hens fed R diet (18.7, − 11.4, and 22.6%, respectively) compared with hens fed the C diet (40.7, 0.3, and 28.6%, respectively; P < 0.05). Total N excretion from hens fed the C and R diet was not different (1.16 g/hen/d); however, mass of chamber N remaining in excreta following the 3-wk period was less from hens fed the C diet (1.27 kg) than from hens fed the R diet (1.43 kg). Gaseous emissions of NH3 over the 3-wk period from hens fed the C diet (0.74 kg per chamber) were greater than emissions from hens fed the R diet (0.45 kg). The 3-wk S excretion mass (estimated using the calculation, indigestible marker, and environmental chamber methods, respectively) was greater from hens fed the R diet (1.85, 1.54, and 1.27 kg, respectively) compared with hens fed the C diet (0.24, 0.20, and 0.14 kg, respectively). The 3-wk P excretion was similar between diets (0.68 kg). Results demonstrate that feeding the acidified diet resulted in decreased N emissions, but because of the acidulant fed, greatly increased S excretion and emissions.

Nutritional value of wheat and corn distiller’s dried grain with solubles: Digestibility and digestible contents of energy, amino acids and phosphorus, nutrient excretion and growth performance of grower-finisher pigs

Two experiments were conducted to evaluate the nutritional value of distiller’s dried grains with solubles (DDGS) samples derived from corn, wheat and a wheat/corn blend (4:1). Specifically, the digestibility and digestible contents of energy, amino acids (AA) and P, N and P excretion, and growth performance were determined in grower-finisher pigs. In exp. 1, 12 ileal cannulated barrows (64.6 ± 6.4 kg) had restricted access (2.6 × maintenance) to a wheat-control diet or one of three diets containing 40% DDGS sample of corn, wheat or wheat/corn origin that replaced wheat. For energy, apparent total tract digestibility was highest for wheat (85%; P &lt; 0.05) and did not differ among the DDGS samples (77 to 79%; P &gt; 0.10). Total tract digestible energy (DE) was higher for corn DDGS (4292 kcal kg-1 DM; P &lt; 0.05) than wheat/corn DDGS, wheat DDGS and wheat samples (4038, 4019 and 3807). For lysine, apparent ileal digestibility (AID) was highest for wheat (71%; P &lt; 0.05) and did not differ among DDGS samples (59 to 63%; P &gt; 0.10). The AID lysine content was highest for corn DDGS (0.51% DM; P &lt; 0.05), intermediate for wheat/corn DDGS and wheat DDGS (0.45 and 0.42), and lowest for wheat (0.37%). For P, total tract digestibility was lowest for wheat (15%; P &lt; 0.05) and did not differ among DDGS samples (53 to 56%; P &gt; 0.10). Total N excretion was highest for wheat/corn DDGS and wheat DDGS (55 and 58 g d-1; P &lt; 0.05), intermediate for corn DDGS (44) and lowest for wheat (36). Total P excretion did not differ among DDGS (11 g d-1) and was lowest for wheat (8; P &lt; 0.05). In exp. 2, 100 pigs (52.0 ± 3.3 kg) were fed a wheat-pea control diet or one of three diets containing 25% of the three DDGS samples (3.375 Mcal DE kg-1; 2.50 g SID lysine Mcal-1 DE) for 5 wk. Overall, average daily feed intake (ADFI) and daily gain (ADG) were higher for pigs fed the wheat control diet than the DDGS-containing diets (P &lt; 0.05), but feed efficiency did not differ (P &gt; 0.10). In summary, the digestible nutrient content of wheat DDGS is lower than corn DDGS and higher than wheat. Followin g pre-characterization of digestible nutrient profile, feeding DDGS reduced growth performance indicating that further research is required to improve the nutritional value of DDGS. Key words: Distiller's dried grains with solubles, pig, digestibility, energy, amino acid

Stoichiometry of nutrient excretion by fish: interspecific variation in a hypereutrophic lake

This study investigates how nutrient cycling rates and ratios vary among fish species, with a particular focus on comparing an ecologically dominant detritivore (gizzard shad) to other fishes in a productive lake. We also examined how nutrient cycling rates are mediated by body size (as predicted by allometry theory), and how variation in nutrient cycling is related to body and food nutrient contents (according to predictions of ecological stoichiometry). As predicted by allometry, per capita nitrogen and phosphorus excretion rates increased and mass‐specific excretion rates decreased, with increasing mass. Body phosphorus content was correlated with body mass only in one species, bluegill. Contrary to stoichiometric predictions, there was no relationship between body P and mass‐normalized P excretion rate, or between body N:P and excreted N:P, when all individuals of all species were considered.However, at the species level, we observed some support for a body nutrient content effect on excretion as predicted by stoichiometry theory. For example, gizzard shad had lower body P (high body N:P) and also excreted P at higher rates (lower N:P) than bluegill, which had high body P (lower body N:P). We applied the Sterner (1990) homeostatic stoichiometry model to the two most common species in the study – gizzard shad and bluegill and found that food N:P had a greater effect than consumer body N:P on excreted N:P. This indicates that, in terms of variation among these species, nutrient excretion may be more of a function of food nutrient content than the nutrient content of the consumer. These results suggest that stoichiometry can provide a framework for variation among species in nutrient cycling and for evaluating the ecosystem consequences of biodiversity loss.

Stoichiometry of nutrient excretion by fish: interspecific variation in a hypereutrophic lake

Stoichiometry of nutrient excretion by fish: interspecific variation in a hypereutrophic lake

Limit Feeding of Gravid Holstein Heifers: Effect on Growth, Manure Nutrient Excretion, and Subsequent Early Lactation Performance

A study was conducted to evaluate the effect of limit feeding on growth, feed efficiency, and manure excretion in Holstein heifers and subsequent milk production. Fifty-four gravid Holstein heifers were randomly assigned to replicate pens and fed 1 of 3 experimental diets for 111 d. Experimental diets included an ad libitum-fed control diet containing 11.3% crude protein (CP) and 2.46 Mcal/kg of metabolizable energy (ME). Two limit-fed diets of increased nutrient density were formulated to contain 12.7 and 14.2% CP and 2.55 and 2.68 Mcal/kg of ME, respectively. Feed intakes of limit-fed diets were limited to 90 and 80% of the control diet. Nutrient intake, growth, manure excretion, blood metabolites, behavior, and 150-d lactation performance were evaluated. Heifers fed 80 and 90% of the control diet consumed less dry matter (8.3 and 9.0 vs. 9.7 kg/d), but similar amounts of net energy for gain (9.5 and 9.4 vs. 9.4 Mcal/d) and CP (1.17, 1.15 vs. 1.10 kg/d) as compared with control diet-fed heifers. The weight gain and skeletal growth of heifers were not different, but heifers limit fed at 80 and 90% of the control had improved feed efficiency. Heifers limit fed at 80 and 90% of ad libitum intake excreted 0.86 and 0.36 kg/d less dry matter, respectively, as compared with control diet-fed heifers, but all heifers excreted similar amounts of N and P. Limit feeding did not affect calf birth weight, dystocia, or lactation performance. Limit feeding gravid heifers improved feed efficiency and reduced manure dry matter excretion without negative effects on lactation performance.

Effects of common carp on nutrient dynamics and littoral community composition: roles of excretion and bioturbation

We manipulated through an enclosure experiment the presence and absence of small common carp (Cyprinus carpio, L) and their sediment access using a mesh net. The aims of the experiment were to determine carp effects on nutrient dynamics and community composition, and partially separate bioturbation effects from the remaining carp effects such as excretion and predation. During the two months, carp influenced water quality and nutrient dynamics, altered phytoplankton biomass and composition and decreased submerged macrophyte biomass independently of sediment access, indicating that nutrient excretion was the primary mechanism for the carp effects. However, Secchi depth decreased while the concentration of suspended solids increased when carp access to the sediments was allowed, suggesting that bioturbation by carp influenced water transparency. Increase in phytoplankton (dominated by cyanobateria) and suspended solids resulted in reduced submerged macrophyte biomass through reduction of light availability. Zooplankton, numerically dominated by rotifers, increased in carp enclosures. In addition, benthic macroinvertebrates decreased in carp enclosures, regardless of the presence and absence of the netting. Because direct predation effects were not evident, carp probably affected benthic macroinvertebrates through reduction of submerged macrophytes. These results indicate that carp can have dramatic direct and indirect impacts on nutrient dynamics and littoral community structure through excretion and bioturbation. Ecosystem engineering by carp may therefore trigger a shift from a clear water state dominated by submerged macrophytes to a turbid water state dominated by phytoplankton.

Predicting the profile of nutrients available for absorption: from nutrient requirement to animal response and environmental impact

Current feed evaluation systems for dairy cattle aim to match nutrient requirements with nutrient intake at pre-defined production levels. These systems were not developed to address, and are not suitable to predict, the responses to dietary changes in terms of production level and product composition, excretion of nutrients to the environment, and nutrition related disorders. The change from a requirement to a response system to meet the needs of various stakeholders requires prediction of the profile of absorbed nutrients and its subsequent utilisation for various purposes. This contribution examines the challenges to predicting the profile of nutrients available for absorption in dairy cattle and provides guidelines for further improved prediction with regard to animal production responses and environmental pollution.The profile of nutrients available for absorption comprises volatile fatty acids, long-chain fatty acids, amino acids and glucose. Thus the importance of processes in the reticulo-rumen is obvious. Much research into rumen fermentation is aimed at determination of substrate degradation rates. Quantitative knowledge on rates of passage of nutrients out of the rumen is rather limited compared with that on degradation rates, and thus should be an important theme in future research. Current systems largely ignore microbial metabolic variation, and extant mechanistic models of rumen fermentation give only limited attention to explicit representation of microbial metabolic activity. Recent molecular techniques indicate that knowledge on the presence and activity of various microbial species is far from complete. Such techniques may give a wealth of information, but to include such findings in systems predicting the nutrient profile requires close collaboration between molecular scientists and mathematical modellers on interpreting and evaluating quantitative data. Protozoal metabolism is of particular interest here given the paucity of quantitative data.Empirical models lack the biological basis necessary to evaluate mitigation strategies to reduce excretion of waste, including nitrogen, phosphorus and methane. Such models may have little predictive value when comparing various feeding strategies. Examples include the Intergovernmental Panel on Climate Change (IPCC) Tier II models to quantify methane emissions and current protein evaluation systems to evaluate low protein diets to reduce nitrogen losses to the environment. Nutrient based mechanistic models can address such issues. Since environmental issues generally attract more funding from governmental offices, further development of nutrient based models may well take place within an environmental framework.

C–N mismatch in the leaf litter–shredder relationship of an Andean Patagonian stream detritivore

Aquatic shredders depend mostly on terrestrial leaf litter as a food resource, and differences between the C:N ratio of their food resource and their bodies may affect nutrient excretion and the composition of their feces. Laboratory experiments were used to test how the stonefly Klapopteryx kuscheli rebalances the high C:N ratio of its food. An experiment was designed in which K. kuscheli was fed 5 different leaf litters across a gradient of C:N ratios and the elemental ratios of the food, insect bodies, and feces were analyzed. Klapopteryx kuscheli regulated its internal elemental composition by changing its excretion of N depending on the N content of its food. An inverse relationship was found between N content of most foods and excreted NH4+. However, K. kuscheli feces were rich in N and the insect excreted very small amounts of NH4+ when fed Nothofagus pumilio, probably because of refractory N-based compounds in the leaves of this species. Homeostatic regulation of N content by invertebrate shredders may influence N dynamics in small nutrient-poor streams.

Seasonal patterns of pore-water nutrients, benthic chlorophyll a and sedimentary AVS in a macrobenthos-rich tidal flat

Monthly field investigations were carried out at controlled low-tide in an estuarine intertidal sandflat of the Seto Inland Sea (Japan) between January 1995 and April 1996. We assessed the spatial and temporal distribution of pore-water nutrient [NH4+-N, (NO3− + NO2−)-N, PO43−-P and Si(OH)4-Si], chlorophyll a (chl a) and acid-volatile sulphide (AVS) concentrations in the uppermost 0–10 cm sediment horizon, and evaluated their relationships with macrobenthic assemblages. Monthly hydrological data, nutrient and chl a concentrations in low-tide creek water adjacent to the flat were used as a complementary environmental characterisation of the study area. All different pore-water nutrients showed a 10 to > 30-fold variability between different layers and periods. NH4+-N, PO43−-P and Si(OH)4-Si concentrations were lowest in winter, progressively increased throughout spring and summer, and were highest between September and October, with a major increase at intermediate (4–8 cm) layers. In contrast, (NO3− + NO2−)-N concentrations, correlated positively with chl a, peaked in winter and sharply decreased with depth in all different seasons and in most occasions. Depth-integrated NH4+-N, PO43−-P and Si(OH)4-Si pools were correlated positively with biogenic nutrient flux calculated from the nutrient excretion rates of dominant bivalves Ruditapes philippinarum and Musculista senhousia. These relationships indicated rapid removal pathways of P, Si and N (i.e., every 0.1, 0.24 and 0.34 day, respectively), implying highly dynamic sediments. Based on the mass balance P = F + I, biogenic production (P) vs. diffusive flux (F) estimates suggested a predominant contribution of animal bioirrigation (I) to the upward flux of nutrients. AVS concentrations, correlated negatively with both (NO3− + NO2−)-N and chl a, showed a progressive increase from late summer throughout winter, subsequent to that of NH4+-N, PO43−-P and Si(OH)4-Si. The results indicate that in our study area the spatial and temporal distribution of pore-water nutrients, chl a and AVS in sediments are strongly interlinked and suggest that the metabolic processes (e.g., excretion, bio-deposition) and behavioural activities (e.g., particle mixing, bioirrigation) of abundant macrobenthos play an important role in the year-round biogeochemical processes occurring on this flat.

Alien vs. endemic crayfish: roles of species identity in ecosystem functioning

In northern Japan, an alien crayfish species (signal crayfish; Pacifastacus leniusculus) is replacing Japan's only native crayfish species (Cambaroides japonicus) that is endemic to the country. We tested experimentally if these two crayfish species had similar roles in terms of ecosystem functioning in stream habitats. Experiments were performed to examine the impacts of alien and endemic crayfish on detritus-based food webs. During the experiment, neither crayfish species affected rates of breakdown of microbially conditioned oak leaves. In contrast, the amphipod Jesso-gammarus jesoensis, which dominated the non-crayfish invertebrate biomass, was significantly reduced in the presence of the two crayfish species. Thus, effects of crayfish on leaf breakdown were probably masked by the leaf processing activities of these large amphipods in the absence of crayfish. Overall, per-unit biomass impacts of Pacifastacus on leaf processing and invertebrate colonisation of leaves were comparable to those by Cambaroides. Laboratory experiments were performed to test whether rates of leaf processing of 10 riparian plant species, particulate organic matter (POM) production and nutrient excretion differed between crayfish species in the absence of other invertebrates. Although POM production rates did not differ between crayfish species, crayfish impacts on leaf processing differed depending on plant species reflecting differential leaf preference. Comparisons of individual nutrient excretion rates revealed that ammonia and phosphate excretion rates were higher in Cambaroides compared with Pacifastacus. Further, ammonia excretion rates were proportional to crayfish biomass in Cambaroides but not in Pacifastacus. Taken together, the two crayfish species had similar roles in stream food webs when biomass was similar. However, their roles as leaf processors and excretion rates of nutrients differed when there was a choice among different riparian species as sources of leaf litter. Species replacement between alien and endemic crayfish may therefore result in differential consequences for ecosystem processes.