Amiram Shkolnik

Blood-gas properties and function in the fossorial mole rat under normal and hypoxic-hypercapnic atmospheric conditions

Blood and tissue gas exchange properties of mole rats in normoxic and hypoxic-hypercapnic conditions were compared to the common mammalian pattern. RBC count was 14.0 +/- 1.2-10(6)/microliter. Hb concentration was 15.0 +/- 0.4g/100 ml. P50 (at pH 7.4 and 37 degrees C) was 29.5 +/- 0.5 mm Hg. Oxygen capacity averaged 20.2 +/- 0.4 vol% and the Hill coefficient was 2.9 +/- 0.1. The Bohr effect was -0.53 +/- 0.02 (deltalog P/deltapH). The temperature coefficient was 0.0152 +/- 0.0014 (deltalog P/delta degrees C). The Haldane effect was 4.8 +/- 0.5 (deltaCCO2 vol%)at PCO2 =40 mm Hg. Steady-state partial pressures in gas pockets were PO2 = 15.1 +/- 1.4 mm Hg and PCO2 = 85.8 +/- 3.9 mm Hg in normoxia, and 11.5 +/- 3.0 and 101.8 +/- 3.5 repectively in hypoxia-hypercapnia (PIO2 congruent to 85 mm Hg). Under the same conditions 2,3-DPG dropped from 0.87 and 0.88 to 0.62 and 0.65 (mol/mol Hb) in the rat and in the white rat, respectively. Heart muscle myoglobin concentration of the mole rat (1.44 mg/g) did not differ significantly from that of the white rat (1.96 mg/g), whereas masseter myoglobin was 4.0 mg/g--significantly different from the rat (1.21 mg/g). Results indicate that the strategy used by the mole rat to maintain a normal metabolic rate under variable atmospheric conditions, besides having high oxygen affinity, is to expand the physiological range of the oxygen dissociation curve to very low oxygen tensions, at the expense of its acid-base regulation. The regulation of the shape of the oxygen dissociation curve is discussed.

Comparison of rate of passage, fermentation rate and efficiency of digestion of high fiber diet in desert Bedouin goats compared to Swiss Saanen Goats

Fermentation and passage rate in the rumen and along the entire gut were measured in black Bedouin and Swiss Saanen goats fed a high fiber diet (Rhodes grass (Chloris guyana) supplemented with 10% alfalfa hay). The purpose of the study was to clarify the physiological basis that underlies advantages of Bedouin goats over non-desert goats in digesting high fiber based diets. Volume of fluid and rumen digesta particle distribution were similar for both breeds. Ability of Bedouin goats to consume amounts of hay equal to those consumed by Saanen goats, despite considerably longer retention time in the rumen, was related to their ability to maintain a higher digestion rate in the rumen. Microbial activity in the particulate fraction was higher in Bedouin goats than in Saanen goats, and this was reflected in total rumen fermentation, i.e., in significantly higher volatile fatty acid production rate and significantly higher volatile fatty acid concentrations. The ability of Bedouin goats to maintain a high fermentation rate in the rumen may be partially related to their ability to control rumen pH above levels which cause severe depression in rate of fermentation. The combination of higher fermentation rate and slower passage allows maximization of feed intake and digestibility in a given situation, as compared to non-desert ruminants.

Homeostatic responses to water deprivation or hemorrhage in lactating and non-lactating bedouin goats

Three lactating and three non-lactating black Bedouin goats were subjected to four days of water deprivation or to hemorrhage. Four days of water deprivation caused body wt losses of 32 and 23% and plasma volume losses of 30 and 34% in lactating and non-lactating goats respectively. Plasma osmolality increased 17 and 15% in lactating and non-lactating goats. Plasma arginine vasopressin concentration rose from about 5 pg/ml to a mean of 36 pg/ml. Plasma renin activity increased from about 0.7 ng/ml/hr to a mean of 3.45 ng/ml/hr in lactating and to 3.15 ng/ml/hr in non-lactating goats. At 4.5 hr post-rehydration plasma osmolality and plasma vasopressin concentration were back to normal in non-lactating, but still elevated in lactating goats. Plasma renin activity increased after rehydration. Rapid blood volume loss of 21-28% increased plasma vasopressin concentration to 16-35 pg/ml in non-lactating and to 70 or greater than 500 pg/ml in lactating goats. It is concluded that black Bedouin goats are well adapted to endure severe dehydration and rapid rehydration, but that they (especially lactating animals) react strongly to rapid volume depletion.

Gross energy digestion and urea recycling in the desert black Bedouin goat

Abstract 1. 1. Gross energy digestion and urea recycling were measured in Bedouin goats inhabiting extreme deserts in the Middle East and compared to Swiss Saanen goats. 2. 2. The apparent gross energy digestibility of alfalfa hay and wheat straw in the black Bedouin goat were 6% and 33% respectively higher than in the Swiss goat. 3. 3. When the amount of alfalfa hay fed was restricted to about 60–70% of the ad lib consumption, recycling of urea in the Bedouin goats was maintained at rates (0.44g·N-urea [kg·day] −1 ) similar to those recorded when alfalfa hay was fed ad lib . In the Swiss goats a 30% drop was recorded. 4. 4. When wheat straw was the only feed, the amount of urea recycled by the Bedouin goats (0.18 g·Nurea [kg·day] −1 ) was more than twice the amount recycled by the Swiss goats. 5. 5. Supplementing the wheat straw to provide both breeds with equal amounts of digestible energy and nitrogen intake resulted in an increase in the amount of urea recycled in both breeds. The Bedouin goat, however, still recycled twice as much urea (0.3 g·N-urea [kg·day] −1 ) as the amount recycled by the Swiss goats. 6. 6. It was concluded that under adverse nutritional conditions the Bedouin goat possesses high potentials to both meet its caloric demands as well as to economise its nitrogen metabolism and the two characteristics are complementary to each other.

Rapid Rehydration and Kidney Function in the Black Bedouin Goat

Black goats, tended by Bedouin tribesmen in the extreme deserts of the Middle East, drink only once every 2-4 days and imbibe amounts of water that often exceed 40% of their dehydrated body weight. The water that the goats drink copiously is first retained in the rumen and only gradually flows into the other body fluid compartments. Five hours after the drinking, 81% of the water imbibed was still stored in the spacious rumen of the goat. The kidney of the Bedouin goat responded to the voluminous drinking by a drop in the blood flow that was followed by a compatible drop in both the GFR and the urine flow. The urine flow, even 4 h following the drinking, was below the rate recorded in the dehydrated animal. Urine Na⁺ concentration that amounted to 80.3 mM in the dehydrated animal dropped to only 37.7 mM following the drinking. A drop (from 144 mM to 49 mM) was also simultaneously recorded in Cl⁻ concentration; K⁺ and urea concentration, however, changed only slightly. It is suggested that the rumen in the goat serves as a water reservoir that helps maintain the osmotic stability of the body proper. The kidneys in these animals efficiently conserve the water imbibed as well as the bodys Na⁺ and Cl⁻. Studies of sheep that assign similar roles to the rumen and the kidneys indicate that the physiological mechanism described in the present study is generally shared by ruminants tended in a pastoral system.

Effects of infrequent drinking on the nitrogen metabolism of Bedouin goats maintained on different diets

The effect of infrequent drinking on nitrogen metabolism was studied in Bedouin goats, a breed herded in the extreme deserts of the Middle East. The goats were given water either daily or only once every 4 days, while being maintained on roughages of different quality: lucerne hay (19% protein), Rhodes grass (10% protein) or wheat straw (3·7%). On lucerne hay and Rhodes grass the goats kept their body mass constant, whether given water daily or only once every 4 days. When on wheat straw the body mass was maintained constant only when given water once every 4 days. Infrequent drinking was found to hamper considerably the food intake of the goats when fed on high quality roughage. When on the wheat straw, the nitrogen intake of the goats (only 12% of that recorded when fed lucerne hay and given water daily) was, however, not affected by the drinking regime. Infrequent drinking improved nitrogen digestibility on all the diets, but more so on those of low quality than on the lucerne hay. When tested on the low quality feeds, urea excretion was low and urea retention and recycling were maintained at high rates. Infrequent drinking had no adverse effect on these capacities.

Effect of dehydration and rapid rehydration on renal function and on plasma renin and aldosterone levels in the black Bedouin goat

Bedouin goats in the extreme deserts of the Middle East are regularly subjected to severe dehydration and possess a capacity to rapidly rehydrate by drinking large volumes of water. Urine flow, glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) in the fully hydrated animals amounted to 0.74±0.4 ml · min−1, 76±29 ml · min−1 and 344±146 ml · min−1 respectively. In goats that were dehydrated to a loss of about 30% of their initial body weight, urine flow dropped to 24% of the value recorded in the hydrated animals and GFR and ERPF dropped to half their level recorded in the hydrated phase. Na and K+ excretion decreased in the water depleted goats and further decrease was recorded following drinking. Following drinking the urine flow, GFR and ERPF of the recently rehydrated goats dropped to below the rates recorded in the dehydrated animals. During the 3 h of the continuous recording that followed the drinking, all three rates did not exceed the predrinking level. Plasma renin activity amounted to 0.37±0.32 ng AI·ml−1·h−1 in the hydrated animals. In dehydrated ones it amounted to 4.8±2.8 ng AI·ml−1·h−1 and a further increase was recorded following drinking. Aldosterone in the hydrated goats was 5.5±4.3 ng% and increased to 13.9±2.3 ng% in the dehydrated animal and amounted to 20.1±5.5 ng% 2 h following drinking. It is concluded that the kidney in the Bedouin goat plays a major role in conserving both water and solutes, not only when deprived of water but also following its rapid rehydration.

Thermoregulation in Fat-Tailed Awassi, a Desert Sheep, and in German Mutton Merino, a Mesic Sheep

Rectal temperature, metabolic rate and total evaporative water loss were measured and thermal conductance was calculated in five desert fat-tailed Awassi and in five mesic German Mutton Merino (GMM) ewe lambs. Measurements were made under laboratory conditions between 20 and 40 C Ta and at a relative humidity of 30%. Both breeds remained thermostable. The mean daily basal metabolic rate of the Awassi was 57.4 kcal/kg0.75, which is 18% below the predicted, and of the GMM was 60.2 kcal/kg0.75, which is 14% below the predicted. None of the Awassi sheep increased their metabolic rate above the basal level at Ta of 40 C; two of the GMM did and panted vigorously. Both breeds increased their total evaporative water loss as the Ta increased; the GMM at a faster rate. Thermal conductance was similar in the two breeds between 20 and 30 C Ta. At 35 C there was a sharp increase in conductance in the Awassi, whereas conductance in the GMM remained stable. It appears that the Awassi lost more heat than the GMM through means other than the evaporation of water, whereas the GMM used more evaporative water. It may be concluded that both breeds responded similarly to moderate Tas; however the Awassi showed better ability to withstand high Tas.

Rapid rehydration in the black bedouin goats: Red blood cells fragility and role of the rumen

Abstract 1. 1. Following dehydration, Bedouin goats regularly drink volumes of water amounting to 30–40% of their bodyweight. 2. 2. In vitro experiments showed that 50% hemolysis of the red blood cells of these goats occurred at a concentration of 110 mM NaCl. 3. 3. Blood plasma concentration dropped from 336.5± 6.9 mOsm/Kg before drinking, to only 303.7 ± 7.6, 6 hr afterwards. Changes in plasma volume were moderate too. 4. 4. The rumen was shown to first retain the water imbibed, and to release it only gradually later on: within 5 hr following the drinking only 18% of the ruminal fluid left the rumen.

Adaptation to Life in the Desert in the Brown Hare (Lepus capensis)

Adaptations to life in the desert were studied in brown hares ( Lepus capensis ) from the Negev Desert of Israel. For comparison, brown hares from a temperate region in southern France were included in the study. All animals sustained themselves on dry alfalfa hay. The desert hares, however, required, on the basis of their specific metabolic weight, only 75% of the amount of food consumed by the European hares, and their digestive capacity was superior. Resting metabolic rate of the desert hares was 61% of the value recorded in the European hares, and their lower critical temperature was higher. Rate of water turnover was 124 ml kg082 day−1 in the desert hares, only one-half of the value recorded for the European hares. The desert hares were able to drink salt (NaCl) solutions up to a concentration of 6%. Their maximal urine concentration was 4,470 mosmol kg−1. The maximal concentration of the salt solution consumed by the European hares was 2.5% and their maximal urine concentration was 2,500 mosmol kg−1.