Metabolic Water Production Research Articles

Water deprivation induces appetite and alters metabolic strategy in Notomys alexis: unique mechanisms for water production in the desert.

Like many desert animals, the spinifex hopping mouse, Notomys alexis, can maintain water balance without drinking water. The role of the kidney in producing a small volume of highly concentrated urine has been well-documented, but little is known about the physiological mechanisms underpinning the metabolic production of water to offset obligatory water loss. In Notomys, we found that water deprivation (WD) induced a sustained high food intake that exceeded the pre-deprivation level, which was driven by parallel changes in plasma leptin and ghrelin and the expression of orexigenic and anorectic neuropeptide genes in the hypothalamus; these changed in a direction that would stimulate appetite. As the period of WD was prolonged, body fat disappeared but body mass increased gradually, which was attributed to hepatic glycogen storage. Switching metabolic strategy from lipids to carbohydrates would enhance metabolic water production per oxygen molecule, thus providing a mechanism to minimize respiratory water loss. The changes observed in appetite control and metabolic strategy in Notomys were absent or less prominent in laboratory mice. This study reveals novel mechanisms for appetite regulation and energy metabolism that could be essential for desert rodents to survive in xeric environments.

Metabolic, ventilatory and hygric physiology of the chuditch ( Dasyurus geoffroii; Marsupialia, Dasyuridae)

The chuditch is a large carnivorous dasyurid marsupial. Historically it had one of the widest geographical distributions of all marsupials, encompassing much of arid Australia, but it is now restricted to the mesic south-west of Western Australia. It is therefore of interest to determine if its physiology better reflects adaptation to its historically arid or present mesic habitat. The basic physiological parameters of the chuditch conform to other marsupials. Body mass of males (1385 g) was > 400% of that predicted by phylogeny and this may be related to its carnivorous diet. Body temperature was 33.9 °C at ambient temperatures ≤ thermoneutrality, with hyperthermia occurring above thermoneutrality. Basal metabolic rate was 0.361 mL O 2 g − 1 h − 1 at an ambient temperature of 31 °C. Metabolic rate increased below the thermoneutral zone by 0.038 mL O 2 g − 1 h − 1 °C − 1 , and above the thermoneutral zone to 0.444 ± 0.059 mL O 2 g − 1 h − 1 at 33.3 °C. Standard evaporative water loss was 0.498 ± 0.071 mg g − 1 h − 1 at an ambient temperature of 26.0 °C, and increased at higher ambient temperatures due to panting and licking. Changes in wet thermal conductance largely reflected changes in evaporative heat loss, and dry thermal conductance increased at high ambient temperature due in part to posture change. Ventilatory parameters were consistent with metabolic demands in and below thermoneutrality, and suggested augmented evaporative heat loss above the thermoneutral zone. Chuditch had a high point of relative water economy of 22.6 °C, indicating favourable water economy at even moderate ambient temperatures, due to its low evaporative water loss rather than high metabolic water production. Chuditch were physiologically more similar to marsupials from arid rather than mesic habitats, better reflecting their historical distribution than their current geographical range.

Exercise-Associated Hyponatremia

Disorders of serum sodium occur commonly in athletes participating in endurance sports. The most life-threatening of these is hyponatremia, which can occur in as many as 2% to 7% of participants. Exercise-associated hyponatremia (EAH) is caused by a combination of excessive water or hypotonic fluid intake as well as high levels of arginine vasopressin, which limits the ability of the kidney to excrete water. Other factors in the pathogenesis of EAH include sweat sodium loss, inability to mobilize exchangeable sodium stores, metabolic water production, and impaired renal blood flow and glomerular filtration rate. Most cases of EAH lead to minimal or absent complications and do not require specific therapy other than close monitoring and fluid restriction. However, a small number of athletes may present with severe and life-threatening hyponatremia associated with cerebral edema and possibly noncardiogenic pulmonary edema. Rapid diagnosis and appropriate therapy of these athletes with hypertonic saline is required to prevent severe complications or death.

Water homeostasis in bees, with the emphasis on sociality

Avenues of water gain and loss in bees are examined here at two levels of organisation: the individual and the colony. Compared with the majority of terrestrial insects, bees have a high water turnover. This is due to their nectar diet and, in larger species, substantial metabolic water production during flight, counteracted by high evaporative and excretory losses. Water fluxes at the colony level can also be very high. When incoming nectar is dilute, honeybees need to remove large volumes of water by evaporation. On the other hand, water is not stored in the nest and must be collected for evaporative cooling and for feeding the brood. Water regulation has many similarities at individual and colony levels. In particular, manipulation of nectar or water on the tongue is extensively used by bees to increase evaporation for either food-concentrating or cooling purposes.

Why does the Namib Desert tenebrionid Onymacris unguicularis (Coleoptera: Tenebrionidae) fog-bask?

Dehydration of Onymacris unguicularis (Haag) for 10 days at 27°C resulted in a weight loss of 14.9%, and a 37% decrease in haemolymph volume. Although there was an overall decrease in the lipid content during this period, metabolic water production was insufficient to maintain total body water (TBW). Rehydration resulted in increases in body weight (6.2% of initial weight), TBW (to normality), and haemolymph volume (sub-normal at the end of rehydration). Despite an increase of 44.0 mg in the wet weight of O. unguicularis after drinking for 1h, there was little change in the water content at this time, although the total lipid content increased significantly. Increases in haemolymph osmolality, sodium, potassium, chloride, amino acid and total sugar concentrations during dehydration were subject to osmoregulatory control. No evidence of an active amino acid-soluble protein interchange was noted during dehydration or rehydration. Haemolymph trehalose levels were significantly increased at the end of rehydration (relative to immediate pre-rehydration values), indicating de novo sugar synthesis at this time. Osmotic and ionic regulation was evident during rehydration, but control of OP during haemolymph-dilution is poor and accomplished largely by the addition to the haemolymph of free amino acids and solute(s) not measured in this study. There was little mobilization of sodium and chloride ions from storage sites at this time. The lesser osmoregulatory ability of Onymacris unguicularis and perhaps earlier susceptibility to osmotic stress, a significantly high normal blood glycerol level (relative to other diurnal adesmiine tenebrionids), and a water storage mechanism associated with synthesis of fat, probably all contribute to the development of fog-basking behaviour in this species. Water gain in O. unguicularis during periods of relative drought is probably largely accomplished by a greater food consumption.

Reply to Weschler

LETTERS TO THE EDITORReply to WeschlerLindsay B. BakerLindsay B. BakerPublished Online:01 Nov 2008https://doi.org/10.1152/japplphysiol.91087.2008MoreSectionsPDF (30 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat to the editor:We appreciate Dr. Weschler's (5) interest in our paper (1) and gladly take the opportunity to address the two points she raises in her letter, i.e., that 1) “Baker et al.'s findings may represent the first demonstration of osmotic activation and inactivation [of sodium] in controlled experimental conditions” and 2) the experiments in Baker et al.'s paper were “inadequate to test the hypothesis that weight maintenance means addition of body water.”Weschler's first point misinterprets our results. In her letter, Weschler wrote that “Baker et al. found that the changes in serum [Na] were less than predicted when serum [Na] both increased and decreased.” However, the reported results showed no significant difference between the measured and predicted serum [Na+] during the −4%, −2%, or 0% change in body mass (ΔBM) trials (i.e., when measured serum [Na+] increased or did not change from baseline). When subjects drank more fluid than they lost during the hyperhydration trials (i.e., gained 2% of BM), the predicted decrease in serum [Na] was greater than the measured decrease in serum [Na]. In the latter case we proposed a more plausible explanation, stating “Because of the high rate of urine excretion during the +2% ΔBM trials, subjects drank a substantial volume (∼900 ml) of fluid during the 50-min recovery period to compensate for urine losses and maintain +2% ΔBM. It is possible that fluid absorption was not complete and a portion of the ingested fluid volume remained in the subjects’ stomachs at the time of post-experiment BM measurements. Accordingly, at the end of the 50-min recovery period, subjects rated their level of stomach bloating and sloshing of stomach contents significantly higher during the +2% ΔBM vs. the 0%, −2%, and −4%, ΔBM trials. Consequently, measured serum [Na+] was not as diluted as would be predicted by the ΔTBW (total body water) term in the Nguyen-Kurtz equation (1).” We stand behind the veracity of our data and the strength of its interpretation. We do not agree that our findings support the osmotic activation/inactivation of sodium hypothesis.Dr. Weschler's second point, that more work (i.e., a longer running protocol) would result in more fuel oxidation and more metabolic water production, is well taken. However, realistically, endurance athletes are going to ingest carbohydrate to replace oxidative fuel losses, especially if more work is performed. Additionally, metabolic water production (∼0.13 g/kcal) is offset by respiratory water loss (∼0.12 g/kcal) (2, 3), so this results in water turnover with no net ΔTBW, regardless of exercise duration. Furthermore, because glycogen stores are limited (whether glycogen loaded or not), whatever role the release of water complexed to glycogen plays in contributing to total body water would likely occur within our study time frame (2+ h). Therefore, we maintain that our experiment was adequate to refute the notion (4) that 0% ΔBM results in a net increase in TBW during exercise.REFERENCES1 Baker LB, Lang JA, Kenney WL. Quantitative analysis of serum sodium concentration after prolonged running in the heat. J Appl Physiol 105: 91–99, 2008.Link | ISI | Google Scholar2 Consolazio FC, Johnson RE, Pecora LJ. The computation of metabolic balances. In: Physiological Measurements of Metabolic Function in Man. New York: McGraw-Hill, 1963, p. 313–339.Google Scholar3 Mitchell JW, Nadel ER, Stolwijk JAJ. Respiratory weight losses during exercise. J Appl Physiol 32: 474–476, 1972.Link | ISI | Google Scholar4 Noakes TD, Sharwood K, Speedy D, Hew T, Reid D, Dugas J, Almond C, Wharam P, Weschler L. Three independent biological mechanisms cause exercise-associated hyponatremia: evidence from 2,135 weighed competitive athletic performances. Proc Natl Acad Sci USA 102: 18550–18555, 2005.Crossref | PubMed | ISI | Google Scholar5 Weschler LB. Comments on Baker et al.'s “Quantitative analysis of serum sodium concentration after prolonged running in the heat.” J Appl Physiol; doi:10.1152/japplphysiol.zdg-8198.2008.Link | ISI | Google ScholarAUTHOR NOTESAddress for reprint requests and other correspondence: L. B. Baker, Gatorade Sports Science Institute, 617 W. Main St., Barrington, IL 60010 (e-mail: [email protected]) Download PDF Previous Back to Top FiguresReferencesRelatedInformation More from this issue > Volume 105Issue 5November 2008Pages 1693-1693 Copyright & PermissionsCopyright © 2008 the American Physiological Societyhttps://doi.org/10.1152/japplphysiol.91087.2008History Published online 1 November 2008 Published in print 1 November 2008 Metrics

Comments on Baker et al.'s “Quantitative analysis of serum sodium concentration after prolonged running in the heat”

to the editor: Baker et al. ([1][1]) tested the Nguyen-Kurtz equation's ([4][2]) predictive powers for serum [Na]. Briefly, the N-K equation is a mass-balance approach to predicting changes in serum [Na]. Given a starting serum [Na] and total body water and then accounting for changes in body water

High Rates of Energy Expenditure and Water Flux in Free‐Ranging Point Reyes Mountain BeaversAplodontia rufa phaea

We measured water flux and energy expenditure in free-ranging Point Reyes mountain beavers Aplodontia rufa phaea by using the doubly labeled water method. Previous laboratory investigations have suggested weak urinary concentrating ability, high rates of water flux, and low basal metabolic rates in this species. However, free-ranging measurements from hygric mammals are rare, and it is not known how these features interact in the environment. Rates of water flux (210+/-32 mL d(-1)) and field metabolic rates (1,488+/-486 kJ d(-1)) were 159% and 265%, respectively, of values predicted by allometric equations for similar-sized herbivores. Mountain beavers can likely meet their water needs through metabolic water production and preformed water in food and thus remain in water balance without access to free water. Arginine-vasopressin levels were strongly correlated with rates of water flux and plasma urea : creatinine ratios, suggesting an important role for this hormone in regulating urinary water loss in mountain beavers. High field metabolic rates may result from cool burrow temperatures that are well below lower critical temperatures measured in previous laboratory studies and suggest that thermoregulation costs may strongly influence field energetics and water flux in semifossorial mammals.

Using Experimental Evolution to Study the Physiological Mechanisms of Desiccation Resistance inDrosophila melanogaster

Data from populations undergoing experimental evolution can be used to make comparisons between physiologically differentiated populations and to determine evolutionary trajectories. Comparisons of long-established laboratory populations of Drosophila melanogaster that are strongly differentiated with respect to desiccation resistance are used to test alternative hypotheses concerning the mechanisms that fruit flies use to survive bouts of extreme desiccation. This comparative study supports the hypothesis that, in at least one case, D. melanogaster can evolve increased resistance to desiccation by decreasing water loss rates and by increasing bulk water content but not by increasing metabolic water content or dehydration tolerance. While glycogen was involved in water storage, its primary role was in water binding, not the production of metabolic water. Measurement of the trajectories of these component mechanisms during selection for desiccation resistance is used to demonstrate that water loss rate quickly plateaus in response to selection, while water content continues to improve. This disparity reveals the value of studying evolutionary trajectories and the need for longer-term selection studies in evolutionary physiology.

Moist habitats are essential for adults of the Antarctic midge, Belgica antarctica (Diptera: Chironomidae), to avoid dehydration

Desiccation resistance of adult males and females of the midge, Belgica antarctica (Diptera: Chironomidae) was evaluated to determine how this short-lived stage maintains water balance in the dry Antarctic environment. Both sexes had slightly lower water content (|60%) and a higher dehydration tolerance (>30% water loss) than most other insects. Water loss rates were high and increased rapidly at temperatures above 15°C, indicating that the adult midges are more hygric than many other polar terrestrial arthropods. Water gain was accomplished by free water uptake with minimal or no contribution from absorption of water vapor or metabolic water production. Parameters related to water balance did not differ among populations from different islands. Overall, the high water requirements of the adult midge appear to be a significant challenge and presumably dictate that the adult midges must emerge during the brief period when free water is readily available and seek protected microhabitats that facilitate water retention.

Fluid Replacement and Performance During the Marathon

The primary purpose of this review is to relate a universal strategy for replacing fluids to optimise marathon performance. A secondary purpose is to examine common 'matters of debate' that may modify fluid needs to include the importance of realistic convective air flow, metabolic water production and waters of association with glycogen. The metabolic demands of marathon running can result in substantial sweat losses and levels of dehydration consistent with compromised endurance performance. Recommendations are provided to individualise fluid intakes with the goal of preventing excessive dehydration (>2% body mass) as well as weight gain. The minor importance of 'matters of debate' to fluid replacement is also discussed.

Water conservation in fasting northern elephant seals (Mirounga angustirostris).

Prolonged terrestrial fasting is a key element in the life history of elephant seals. While on land seals typically fast without access to fresh water, and thus must maintain positive water balance by reductions in water loss such that they can subsist primarily on metabolic water production (MWP). The terrestrial apnea demonstrated by seals may reduce respiratory evaporative water loss (REWL) to levels that allow seals to make a net gain of water from MWP. We empirically measured REWL in 13 fasting northern elephant seal pups and determined the effects on water conservation of a breathing mode that incorporates a regular pattern of apneas, of > or =1 min in duration, followed by eupneic recovery, compared with a breathing mode with no apneas longer than 20 s and resembling typical breathing patterns in other mammals (normative breathing). Overall REWL fell 41% from 0.075+/-0.013 g min(-1) (mean +/- s.d.) during normative breathing to 0.044+/-0.006 g min(-1) during apneic breathing. The decline in REWL is attributed to a decrease in overall ventilation rate, made possible by a decline in metabolic rate along with an increase in oxygen extraction that would occur during apneic breathing. Data on the range of ambient humidity conditions at the local breeding site were collected and used to bound the range of environmental conditions used in laboratory measurements. Our data showed that the observed variations in ambient humidity had no significant effect on REWL. A combination of apneic breathing and the complex nasal turbinates allows fasting elephant seals to reduce REWL well below the rate of MWP so that they can maintain water balance during the fast.

Carbohydrate Profiles During Cotton Floral Bud (Square) Development

AbstractCotton (Gossypium hirsutum) flower's showy corolla expands rapidly, then senesces quickly. Efficient opening of corollas is important for self‐ and cross‐pollination, and indirectly lint yield. Carbohydrate relations are integral to bud water relations and growth, although they are not well understood. Soluble sugars and starch in developing floral buds and flowers of field‐grown cotton plants were analysed. Buds contained significantly more sugar than starch. Sucrose and its hydrolysis products strongly contributed to increased sugars during corolla expansion, and contributed −0.211 MPa to osmotic potential. Water concentration was constant throughout expansion at 860 g kg−1 FW, suggesting sucrose import and hydrolysis are coordinated with other drivers of expansion. Floral sugar content declined sharply during senescence (69 % in 24 h). Although remobilization to other organs could partially explain this decline, we suggest the possibility that most sugar is broken down via respiration, resulting in the production of metabolic water and the significant 7 % increase in floral water concentration during senescence. In summary, imported sucrose and its hydrolysis products increased rapidly during cotton floral bud growth, and supported bud expansion by decreasing the water potential of bud tissue.

Validation of Water Flux and Body Composition in Glaucous Gulls (Larus hyperboreus)

Water influx rates (WIR) measured with tritiated water dilution were compared with direct measures of water and energy intake in glaucous gulls (Larus hyperboreus). Total body water (TBW) measured isotopically was also compared with TBW determined by body composition analysis (BCA) of the same birds. Seventeen wild gulls were captured and studied in outdoor enclosures at Ny-Alesund, Svalbard, in July 2002. Gulls were hand-fed known quantities of Arctic cod (Boreogadus saida) or given water on the basis of one of four experimental treatments: (A) fasting, (B) fish only, (C) water only, or (D) fish and water. Water and energy content of Arctic cod was also determined. WIR of gulls (after subtracting metabolic water production) in treatments A, B, C, and D were 0, 101 +/- 5, 62 +/- 19, and 122 +/- 21 SD g d(-1), respectively. Measured water intake in each group was 0, 111 +/- 2, 64 +/- 3, and 134 +/- 15 SD g d(-1), respectively. On average, WIR underestimated measured water intake in each group. Errors were lowest but most variable for gulls fed water only (-2.2% +/- 32.8%) compared with gulls fed fish only (-9.0% +/- 5.4%) or fish and water (-9.0% +/- 7.0%). Compared with measured water intake, errors in WIR were relatively low overall (-6.9% +/- 17.4%) and comparable to previous validation studies. The difference in TBW determined by BCA versus isotopic dilution ranged between -1.02% and +8.59% of mass. On average, TBW measured isotopically (632 +/- 24 g kg(-1)) overestimated true body water by a factor of 1.033.

Water management in nectar-feeding birds

nectarivory is widespread in birds, but best known in three unrelated families on different continents: the American hummingbirds, Australasian honeyeaters, and the sunbirds of Africa and Asia. Bird pollinators require substantial nectar rewards and their flowers produce copious nectar, which is,

Effect of torpor on the water economy of an arid-zone marsupial, the stripe-faced dunnart (Sminthopsis macroura)

Metabolic rate and evaporative water loss (EWL) were measured for a small, arid-zone marsupial, the stripe-faced dunnart (Sminthopsis macroura), when normothermic and torpid. Metabolic rate increased linearly with decreasing ambient temperature (T(a)) for normothermic dunnarts, and calculated metabolic water production (MWP) ranged from 0.85+/-0.05 (T(a)=30 degrees C) to 3.13+/-0.22 mg H2O g(-1) h(-1) (T(a)=11 degrees C). Torpor at T(a)=11 and 16 degrees C reduced MWP to 24-36% of normothermic values. EWL increased with decreasing T(a), and ranged from 1.81+/-0.37 (T(a)=30 degrees C) to 5.26+/-0.86 mg H2O g(-1) h(-1) (T(a)=11 degrees C). Torpor significantly reduced absolute EWL to 23.5-42.3% of normothermic values, resulting in absolute water savings of 50-55 mg H2O h(-1). The relative water economy (EWL/MWP) of the dunnarts was unfavourable, remaining >1 at all T(a) investigated, and did not improve with torpor. Thus torpor in stripe-faced dunnarts results in absolute, but not relative, water savings.

Water balance in goats subjected to feed restriction

The effect of feed restriction on water balance and nutrient utilization was investigated in individually penned Boer × Saanen kids. Twenty-two male Boer × Saanen kids with an initial average live weight (LW) of 15 kg were used. Seven kids were slaughtered at the beginning of the experiment (reference animals) and the remainders were allocated to one of the three treatments (0, 30 and 60% restriction) and therefore there were five kids per treatment. The feed intake for the 0% restriction treatment animals determined the intake for the animals in the 30 and 60% restriction treatment. When the animals in the 0% restriction treatment group reached 25 kg LW, the animals in the 30 and 60% restriction treatment groups were also slaughtered. There was a negative relationship between DMI and water intake. The digestibility coefficients for DM, OM, carbohydrates, ash, ether extract, energy, NDF, ADF and lignin did not differ between treatments, whereas the digestibility coefficient for CP was different between treatment groups. The highest metabolic water production was in animals in the 0% restriction treatment group. No significant differences were observed in the composition of gastro-intestinal tract contents of the goats in the different treatments. Lower water retention was found in the animals in the 60% restriction treatment group. The study showed that feed restriction affected water intake, CP digestibility and water retention in the body of the kid goats. This experiment demonstrated that DM:water intake ratio changed when severe feed restriction was applied (60% restriction) and water was freely available. It shows a different pattern of behaviour of penned goats, particularly if feed intake is restricted and perhaps caution is needed to extrapolate results from nutritional and physiological trials in pens to goats at pasture.

Comparison of mass-transfer and isotopic dilution methods for estimating milk intake in Antarctic fur seal pups

The efficacy of a new mass-transfer method for estimating milk intake was examined in Antarctic fur seals (Arctocephalus gazella) at Iles Kerguelen. Our method differed from previous mass-transfer approaches in that we estimated milk-mass transfer as the maternal mass lost (MML; kg) during an attendance bout, less the mass lost to metabolic maintenance (MMLE) over that time. MML was significantly related to pup mass-gain (PMG) and attendance bout duration (d days) as follows: MML=1.106PMG+1.002d (r2=0.998). Based on this and previous studies, we estimated that the MMLE was 0.0285 kg kg−1 day−1 for lactating females; and we developed the following milk-mass transfer equation: MMLM=1.106PMG+1.002d−0.0285MMd (where MM is maternal mass). Milk-mass intake was also estimated in an additional 21 pups, using the isotopic dilution method. These values were then compared with estimates based on the milk mass-transfer equation for the same individual pups. A pair-wise comparison indicated that milk-mass transfer estimated using tritium dilution methods were significantly lower than those based on mass-transfer (MMLM). Furthermore, the absolute PMG exceeded tritium dilution estimates of milk-mass transfer in 35% of cases. In contrast, all milk-mass transfer estimates using the mass transfer method were greater than PMG. Overestimation of metabolic water production (MWP), leading to a smaller proportion of the total water intake being attributed to milk ingestion, is believed to be the most likely cause for significant underestimation of milk-mass transfer using the tritium dilution method. Consumption of exogenous water by pups is the most likely reason for the overestimation of MWP, although errors in estimated milk water content may have also contributed to underestimates. We conclude that, in our study, the mass-transfer method provided a more reliable estimate of milk-mass transfer than the isotopic dilution method; and we argue that, under certain conditions, it provides a practical alternative method where the assumptions of isotopic dilution methodology (e.g., all exogenous water from maternal milk) and quantitative parameters (e.g., maternal milk water content) may either be violated or impractical to measure.

Effect of water deprivation on dry matter intake, nutrient utilization and metabolic water production in goats under semi-arid zone of India

Effect of water deprivation on dry matter (DM) intake, nutrient digestibility, nitrogen retention and metabolic water production was studied in bucks of Sirohi, Marwari and Kutchi breeds during August–September. Eighteen adult bucks (4–4.5 years of age), six each of the above-mentioned breeds were divided into three treatment groups in such a way that each group had two bucks of each breed. Water was made available ad libitum to group I, once daily at 15 h to group II and once after 48 h (alternate day) at 15 h to group III. Animals were offered 400 g per buck per day of a pelleted concentrate mixture in the morning and it was consumed by them within 15–20 minutes. Animals were then offered ad libitum pegion pea ( Cajanus cajan) straw. The green grass ( Cenchrus ciliaris) 1 kg per buck per day was provided after watering at 15.30 h. Refusals were recorded next morning at 8.30 h daily. The experiment continued for a period of 60 days following an adjustment period of one month. Dry matter intake (g kg W −0.75 per day) was the lowest in group II (77.53) and the highest in group I (82.91). Total water intake (per kilogram DM intake) ranged from 2.33 l per buck per day in group III to 2.77 l per buck per day in group I. Water deprivation did not effect ( P>0.05) DM intake, nutrient digestibility, nitrogen retention and metabolic water production. The study showed that water deprivation up to 48 h does not adversely affect feed intake and nutrient digestibility in non-producing adult goats.

Moisture Relationships in Composting Processes

Moisture is a key environmental factor that affects many aspects of the composting process. Biodegradation kinetics are affected by moisture through changes in oxygen diffusion, water potential and water activity, and microbial growth rates. These relationships are made more complex by the dynamic nature of the composting process, with changes in particle size and structure occurring over time. A deductive model of the effects of moisture on composting kinetics has defined these relationships based on fundamental physical properties and biological mechanisms. This study applies this model to experimental data from a manure and papermill sludge composting system. The results demonstrate that the optimum moisture content for biodegradation can vary widely for different compost mixtures and times in the composting process, ranging from near 50 to over 70% on a wet basis. While there is a significant reduction in biodegradation rate when operating outside the optimum range, the results also suggest opportunities to mitigate this effect through manipulation of substrate density and particle size. This framework for engineering analysis demonstrates the importance and challenges of maintaining optimum moisture content in dynamic composting systems, where biological drying, metabolic water production, and changes in compaction and porosity are all occurring over time.