Water economy of the Somali donkey
01 Nov 1970-American Journal of Physiology (American Physiological Society)-Vol. 219, Iss: 5, pp 1522-1527
About: This article is published in American Journal of Physiology.The article was published on 1970-11-01. It has received 78 citations till now. The article focuses on the topics: Somali & Donkey.
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TL;DR: In this paper, the authors review available scientific literature on thermoregulation, water balance, and the effects of dehydration in desert ungulates and discuss the physiological, morphological, and behavioral mechanisms used by ungulate to maintain temperature and water balance in arid environments.
Abstract: Desert ungulates must contend with high solar radiation, high ambient temperatures, a lack of water and cover, unpredictable food resources, and the challenges these factors present for thermoregulation and water balance. To deal with the conflicting challenges of maintaining body temperature within acceptable limits and minimizing water loss, desert ungulates use a variety of physiological, morphological, and behavioral mechanisms. The mechanisms involved in thermoregulation and water balance have been studied in many domestic and wild African and Middle Eastern ungulates; studies involving ungulates inhabiting North American deserts are limited in comparison. Our objectives were to review available scientific literature on thermoregulation, water balance, and the effects of dehydration in desert ungulates. We discuss the physiological, morphological, and behavioral mechanisms used by ungulates to maintain temperature and water balance in arid environments, and the implications for research and management of desert ungulates in western North America.
190 citations
Cites background from "Water economy of the Somali donkey"
...However, when dehydrated, some species (e.g., Grant’s gazelle, Thomson’s gazelle, oryx, eland, wildebeest [Connochaetes taurinus], impala, camel) reduce sweating and the rate of cutaneous evaporation by 12–89% (Schmidt-Nielsen et al. 1957, Schoen 1968, Maloiy 1970, Taylor 1970b)....
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...Desert-adapted species (e.g., Somali donkey [Equus asinus], camel, Bedouin goat) are able to drink water equivalent to 20–40% of their body mass in one visit to a water source, which is initially retained in the rumen (Maloiy 1970, Choshniak and Shkolnik 1977, Turner 1979, Silanikove 1994)....
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TL;DR: The sections in this article are: Matching Food Intake, Throughput, Breakdown, and Absorption: Integrative Models, Fermentation, andAbsorption, and Toward an Ecological Physiology of Food Exploitation.
Abstract: The sections in this article are:
1
Matching Food Intake, Throughput, Breakdown, and Absorption: Integrative Models
1.1
Utility of the Modeling Approach
1.2
General Features of Reactor-Based Models
1.3
Reactor Models Applied to Animal Guts
2
Optimizing Retention Time to Rate and Efficiency of Nutrient Extraction
2.1
Matching Overall Digesta Retention Time to Metabolic Needs
2.2
Matching Pulsatile Patterns of Food Intake to Continuous-Flow Digestive Systems
3
Chemical Breakdown
3.1
Survey of Chemical Breakdown of Food Components across Vertebrate Species
3.2
Specific Modulation of Catalytic Enzymes within Species in Relation to Diet
3.3
Modulation of Catalytic Enzymes during Development
4
Microbial Fermentation
4.1
Microbial Habitats in the Gut
4.2
Rates of Fermentation
4.3
Models of Fermentation Systems
4.4
Modulation of Fermentation Capacity and Digesta Retention
4.5
Modulation of Retention Times of Digesta Components
5
Absorption
5.1
Pathways for Absorption of Organic Solutes
5.2
Mechanistic Bases for Differences in Absorption within and between Species
5.3
Nutrient Absorption and Dietary Composition
5.4
Developmental Adaptation to Diet
5.5
Nutrient Absorption and Level of Food Intake
5.6
Absorption in Relation to other Digestive and Metabolic Processes
6
Water and Electrolytes
6.1
Mechanisms of Wafer and Ion Movement across Membranes
6.2
Quantitative Aspects and Adaptive Significance
7
Conclusion
7.1
Toward an Ecological Physiology of Food Exploitation
7.2
Areas for Future Research
151 citations
TL;DR: The view that is most consistent with available information is that gustatory‐alimentary and hepatoportal signals regarding the presence of large amounts of water in the rumen and the absorption of water from the gut activate a range of homeostatic responses involved in fluid and sodium restitution.
Abstract: Ruminants in tropical and desert areas routinely experience cycles of severe dehydration and rapid rehydration. These animals can withstand severe dehydration (18-40% of initial body weight), which exceeds considerably the capacity of most monogastric mammals. This capacity is related to their ability to use, during the course of dehydration, their large water reservoir in the rumen, which contributes 50-70% of the total water loss. As rumen fluid is in approximate isotonicity with systemic fluid, the utilization of gut water during the course of dehydration involves a considerable load of sodium and potassium. Consequently, the effectiveness of utilization of rumen fluid during dehydration depends on the capacity of the kidney to 'desalt' the water absorbed from the gut and on maintenance of salivary flow to the rumen. Following rehydration, ruminants can imbibe their entire water deficit in one drinking and the entire amount ingested is first retained in the rumen. The rumen volume at this stage may exceed the extracellular fluid volume and the sudden drop in rumen osmolality creates a huge osmotic gradient (200-300 mosmol kg-1) between the rumen and systemic fluid. Ruminant animals are confronted at this stage by two opposing tasks, each of them of vital importance: (i) the need to prevent the osmotic hazard leading to water intoxication; and (ii) the need to retain the ingested water, so that it is not missing for the next dehydration cycle. The most prevalent view until recently was a theory which attributes an osmotic protective mechanism to the rumen wall. However, such a capacity has not yet been demonstrated and is challenged by contradictory observations that large amounts of water are absorbed from the rumen following rehydration. The view that is most consistent with available information is that gustatory-alimentary and hepatoportal signals regarding the presence of large amounts of water in the rumen and the absorption of water from the gut activate a range of homeostatic responses involved in fluid and sodium restitution. The efferent elements, presumably activated by the CNS, include: a dramatic increase in secretion of hypotonic saliva and, reciprocally, a dramatic drop in urine flow. The enhanced saliva secretion recycles a considerable portion of the water absorbed from the gut back to the rumen, which allows effective retention of water while avoiding the danger of osmotic threat to the red blood cells. The enhanced saliva secretion also drains large amounts of sodium and bicarbonate from the blood. Accompanying responses are marked retention of sodium and carbonic acid in the kidney.(ABSTRACT TRUNCATED AT 400 WORDS)
133 citations
Cites background from "Water economy of the Somali donkey"
...Voluminous drinking (15-20 % of body weight) was also found in the Somali donkey (Maloiy, 1970), guanaco (Rosenmann & Morrison, 1963), cattle (Siebert & Macfarlane, 1975; Silanikove, 1989 b), sheep (Marfarlane, 1968) and goats (Silanikove, 1991)....
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TL;DR: It is concluded that, although it is generally considered that donkeys can thrive better on poor feeds than ponies, when the animals are allowed ad libitum access to hay and straw better intakes by ponies may compensate for any differences in digestibility seen in donkeys.
Abstract: Summary
Four donkeys and four ponies maintained in climate rooms, were provided with meadow hay or barley straw supplemented with minerals and vitamins ad libitum. Both diets were given to all animals for periods of 21 days. Measurements were made during the last seven days following single doses of two non-absorbable markers (Crfibre and Co-EDTA). After six weeks the donkeys repeated the trial, walking 14 km and ascending 260 m five days per week. At rest ponies ate more than donkeys, however the donkeys showed a higher digestibility of dry matter (DM), organic matter (OM) and acid detergent fibre (ADF) than the ponies. Both species lost weight, ate less and had a lower digestibility of DM, OM and energy on the straw than on the hay ration. Fibre digestibility (neutral detergent fibre [NDF] and ADF) was higher on the straw than the hay diet. Gastrointestinal transit time was slower in the donkeys than in the ponies on both diets. Both species showed a higher mean retention time of digesta on straw than on hay. Exercise had no significant effect on food intake and liveweight changes in the donkeys. Although digestibility coefficients were higher in exercised animals, the effect was not significant. We conclude that, although it is generally considered that donkeys can thrive better on poor feeds than ponies, when the animals are allowed ad libitum access to hay and straw better intakes by ponies may compensate for any differences in digestibility seen in donkeys. Intake of barley straw by both species was not sufficient to meet maintenance requirements.
108 citations
TL;DR: It is argued that terrestrial insects owe much of their success to their ability to recover virtually all the water from the slow flow of primary excretory fluid and to maintain in circulation high concentrations of substances such as amino acids, trehalose, and lipids.
Abstract: Insects have a slowly operating excretory system in which the passive rate of movement of haemolymph solutes into a slowly secreted primary excretory fluid is restricted by a reduction in the area available for passive transfer. They may have come to possess such an energy-saving system as a result of their evolution as small animals in osmotically and ionically stressful environments. Although the possession of a waxy cuticle is a major element in their ability to live in such environments, insects have a very high surface-area/volume ratio and this is likely to have conferred a selective advantage on individuals able to withstand unusually variable extracellular conditions. Among their major adaptations evolved to allow them to tolerate such conditions are the lack of a blood-borne respiratory pigment to be affected and the development of a system whereby their most sensitive tissues are protected by the regulatory activities of special covering epithelia. Because of these features it follows that there has been less evolutionary pressure for rapid excretory control of the haemolymph composition. With an excretory system that only slowly filters the haemolymph, less energy expenditure is involved in the production of the primary excretory fluid and in reabsorption of useful substances from it. In addition, insects are able to maintain in circulation high concentrations of substances such as amino acids, trehalose, and lipids. They can also eliminate excess fluid at very high rates with the loss of only trace amounts of haemolymph solutes. It is argued that terrestrial insects owe much of their success to their ability to recover virtually all the water from the slow flow of primary excretory fluid. The hindgut cells that are responsible for this recovery are aided by their cuticular lining which protects them from contact with the very high concentrations of potentially interfering compounds in the excretory material.
103 citations