Physiological constraint to food ingestion in a new world nectarivorous bat

We investigated the intake response of the nectarivorous Pallas's long-tongued bat Glossophaga soricina to different nectar concentrations to test the hypothesis that bats show compensatory feeding. Bats were offered sucrose solutions between 146 and 1,168 mmol L(-1). Contrary to our expectations, long-tongued bats did not show compensatory feeding, suggesting that volumetric food intake is physiologically constrained. Energy intake was lower at the most dilute solutions (146-584 mmol L(-1)) and then remained relatively constant at more concentrated diets (876 and 1,168 mmol L(-1)). The shape of the observed intake response was very similar to the one predicted by a model dependent on intestinal morphology and in vitro sucrase activity. However, the model predicted higher volumetric food intake at the lower concentrations tested, which suggests that the intestines of the bats were not functioning to their full capacity. Rates of sucrose hydrolysis and water processing probably constrain food intake in long-tongued bats as diets get more dilute.     

The effects of reducing dietary nitrogen and of increasing sodium chloride intake on urea excretion and reabsorption and on urine osmolality in sheep.

Renal responses to reducing dietary nitrogen were studied in four ewes during intravenous infusion of arginine vasopressin. The fall in urea excretion and in plasma urea concentration was accompanied by significant reduction in GFR and in urine osmolality. The fraction of filtered urea reabsorbed increased despite reduction in the urea U/P concentration ratio and this increase was sustained when the urea U/P ratio was further reduced at higher urine flows observed when the drinking water was replaced with saline. This procedure also sustained the RPF which in the absence of additional salt was significantly reduced on the low protein diet. It is suggested that the fall in GFR and the increase in the fraction of filtered urea reabsorbsed may contribute to nitrogen economy and that the increase in fractional reabsorption and the reduction in urine osmolality on the low protein diet provided evidence of active reabsorption of urea by renal tubules.     

The role of urea in nitrogen excretion and caecal nitrogen metabolism in Willow ptarmigan

Summary The fate of¹⁴C-urea, injected intraperitoneally in Willow ptarmigan (Lagopus l. lagopus) has been examined. During five hours 13.6% of the injected activity was recovered in expired CO₂ and 3.5% in urine. Expired activity decreased exponentially with time at a rate corresponding to a half life of 104 min. After Neoterramycin treatment recovery in CO₂ decreased to 7.2% and recovery in urine increased to 8.0%. Specific activity of the caecal content was 7 times higher than average at the end of the experiments. The results indicate that only a minor proportion of the urea from the bird's systemic circulation is excreted in the urine, the major part being hydrolyzed by the caecal microorganisms.     

Effect of increased bromide intake on iodine excretion in rats

The time course of iodine excretion in adult male rats substantially differs from bromine excretion. Bromine is excreted at a single rate, whereas iodine evinces two excretion rates. Even a strong increase in bromide intake in experimental animals failed to affect the rate of iodine excretion but it lowered the fraction of iodine accumulated increase in bromide intake in experimental animals failed to affect the rate of iodine excretion but it lowered the fraction of iodine accumulated in the thyroid gland by 20% probably by affecting the transport of iodide into the thyroid gland.     

Role of urea in the postprandial urine concentration cycle of the insectivorous bat Antrozous pallidus

Insectivorous bats, which feed once daily, produce maximally concentrated urine only after feeding. The role of urea as an osmolyte in this process was investigated in pallid bats (Antrozous pallidus) in the laboratory. Following a 24-h fast, plasma and urine were sampled before and 2 h after feeding in postprandial (PP) animals and before and 2 h after similar treatment without feeding in nonfed (NF) animals. Food consumption by PP animals and handling of NF animals had no effect on blood water content as measured by hematocrit and plasma oncotic pressure. Food consumption increased both plasma osmolality (P(osm)) and plasma urea (P(urea)) by as much as 15%. Food consumption also increased urine osmolality (U(osm)) and urine urea (U(urea)) by 50-100%. Feeding increased U(osm) regardless of changes in P(osm), and elevation of U(osm) resulted primarily from increased U(urea). In NF bats, P(osm) and P(urea) were unchanged, while U(osm) and U(urea) increased by as much as 25%. Again, increased U(osm) resulted primarily from increased U(urea). The PP urine concentration cycle of pallid bats resulted from increased urea excretion in response to apparent rapid urea synthesis. Bats rapidly metabolized protein and excreted urea following feeding when body water was most plentiful.     

Renal excretion of urea in response to changes in nitrogen intake in desert (black Bedouin) and non-desert (Swiss Saanen) goats

• 1.1. Renal responses were compared between desert (black Bedouin) and non-desert (Swiss Saanen) goats fed (a) Lucerne hay ad. lib., (b) Lucerne hay restricted to 65% of the ad. lib. consumption and (c) wheat straw.
• 2.2. Reduced feeding in both breeds resulted in proportional reduction in glomerular filtration rate (GFR) and the amount of urea excreted with no change in the percentage of urea reabsorbed.
• 3.3. In both breeds appreciably less urea was filtered at the glomerulus when a low-nitrogen diet was fed compared with a high nitrogen diet and the percentage of filtered urea reabsorbed increased from about 55 to about 90%.
• 4.4. In both breeds the reduction in GFR is quantitatively more important than the increase in the percentage of filtered urea reabsorbed in regard to renal urea conservation.
• 5.5. The results indicate no qualitative differences between desert and non-desert breeds of goat. The advantages of the Bedouin over the Saanen goats is related to the lower GFR values in the Bedouin goat and mainly their ability to reduce its GFR much more than the Saanen goats in response to lower nitrogen intake.

     

Genetic variation in milk urea nitrogen concentration of dairy cattle and its implications for reducing urinary nitrogen excretion

Nitrogen (N) leached into groundwater from urine patches of cattle grazing in situ is an environmental problem in pasture-based dairy industries. One potential mitigation is to breed cattle for lower urinary nitrogen (UN) excretion. Urinary nitrogen is difficult to measure, while milk urea nitrogen concentration (MUN) is relatively easy to measure. For animals fed diets of differing N content in confinement, MUN is moderately heritable and is positively related to UN. However, there is little information on the heritability of MUN, and its relationship with other traits such as milk yield and composition, for animals grazing fresh pasture. Milk urea nitrogen concentration data together with milk yield, fat, protein and lactose composition and somatic cell count was collected from 133 624 Holstein-Friesian (HF), Jersey (J) and HF×J (XBd) cows fed predominantly pasture over three full lactations and one part lactation. Mean MUN was 14.0; and 14.4, 13.2 and 13.9 mg/dl for HF, J and XBd cows, respectively. Estimates of heritability of MUN were 0.22 using a repeatability model that fitted year-of-lactation by month-of-lactation by cow-age with days-in-milk within month-of-lactation and cow-age, and 0.28 using a test-day model analysis with Gibbs sampling methods. Sire breeding values (BVs) ranged from −2.8 to +3.2 indicating that MUN could be changed by selection. The genetic correlation between MUN and percent true protein in milk was −0.22; −0.29 for J cows and −0.16 for HF cows. Should the relationship between MUN and UN observed in dietary manipulation studies hold similarly when MUN is manipulated by genetic selection, UN excretion could be reduced by 6.6 kg/cow per year in one generation of selection using sires with low MUN BVs. Although J cows had lower MUN than HF, total herd UN excretion may be similar for the same fixed feed supply because more J cows are required to utilise the available feed. The close relationship between blood plasma urea N concentration and MUN may enable early selection of bulls to breed progeny that excrete less UN.     

Nectar intake and energy expenditure in a flower visiting bat

Summary In a coastal region of Venezuela the daily energy expenditure (DEE) and water turnover of the flower visiting bat Anoura caudifer was measured by using the doubly labeled water method. In flower visitors, this method allows independent measurement of energy intake and expenditure if the animals drink no additional water and if the nectar's energy content is known. An average DEE of 12.4 kcal/d and water exchange of 13.4 ml/d were found. Our data show a balanced energy budget when animals in the field imbibe nectar with a sugar concentration of 18–21%, which is roughly medial in the range of nectar concentrations of various bat flowers. The energy turnover of flower visiting bats is high compared with DEEs of other bat species, small mammals and birds; flower visiting bats seem to belong to those species having a fast spin of the life motor.     

畜尿排泄特征及其对草地植被和家畜选择采食的作用

综述了畜尿特征及其对草地植被和家畜选择采食的作用.畜尿主要成分为尿素,尿斑N浓度一般为20～80 g N/m2.家畜排尿量和尿斑大小与家畜种类、饮水次数和放牧季节有关.畜尿空间分布表现为数量和浓度的不同,常呈线形函数形式随机分布于家畜采食路线周围,尿斑中心与边缘的尿N浓度差别很大.通常,畜尿对草地植物的影响限于尿斑区域,约为尿斑面积的2倍,作用时间可持续6～12个月;对草地植物生长具长期促进和短期灼烧作用,其效应大小与尿N浓度和施尿时期有关.一般畜尿促进禾草生长,抑制豆科草的生长和固氮作用.尿斑处植物的N成分比非施尿斑块高,植物吸收的N量随家畜年排泄N不同而异,尿排泄对植物生长的正效应发生于≤250 kg N/(hm2·a)情况下.畜尿排泄增加草地植物多度、丰富度和群落多样性,并受放牧、培育措施的影响.不同植物对畜尿的响应不同,放牧家畜对尿斑不同植物的选食性和补偿性生长差异,是引起和维持草地异质性的重要因素之一.放牧家畜具优先选食和反复采食尿斑植物或高营养斑块的特点,亦经常在远离高营养植被斑块的地方采食.具体草地管理与生产实践中,可通过在草地采食不足的地方设置饮水点、补饲料及搭荫棚等措施,提高家畜对整个草地的利用,以降低家畜对尿排泄物密集区高N植被斑块的过度采食.     

Urinary urea nitrogen excretion during the hyperinsulinemic euglycemic clamp in type 1 diabetic patients and healthy subjects

The hyperinsulinemic euglycemic clamp (HEC) combined with indirect calorimetry (IC) is used for estimation of insulin-stimulated substrate utilization. Calculations are based on urinary urea nitrogen excretion (UE), which is influenced by correct urine collection. The aims of our study were to improve the timing of urine collection during the clamp and to test the effect of insulin on UE in patients with type 1 diabetes (DM1; n=11) and healthy subjects (C; n=11). Urine samples were collected (a) over 24 h divided into 3-h periods and (b) before and during two-step clamp (1 and 10 mIU.kg(-1).min(-1); period 1 and period 2) combined with IC. The UE during the clamp was corrected for changes in urea pool size (UEc). There were no significant differences in 24-h UE between C and DM1 and no circadian variation in UE in either group. During the clamp, serum urea decreased significantly in both groups (p<0.01). Therefore, UEc was significantly lower as compared to UE not adjusted for changes in urea pool size both in C (p<0.001) and DM1 (p<0.001). While UE did not change during the clamp, UEc decreased significantly in both groups (p<0.01). UEc during the clamp was significantly higher in DM1 compared to C both in period 1 (p<0.05) and period 2 (p<0.01). The UE over 24 h and UEc during the clamp were statistically different in both C and DM1. We conclude that urine collection performed during the clamp with UE adjusted for changes in urea pool size is the most suitable technique for measuring substrate utilization during the clamp both in DM1 and C. Urine collections during the clamp cannot be replaced either by 24-h sampling (periods I-VII) or by a single 24-h urine collection. Attenuated insulin-induced decrease in UEc in DM1 implicates the impaired insulin effect on proteolysis.