Modulation of aquaporin 2 expression in the kidney of young goats by changes in nitrogen intake

Genetic studies of heat stress regulation in goat during hot climatic condition

Various direct and indirect environmental constraints have an impact on livestock performance. The physiological parameters, such as rectal temperature, heart rate, and respiratory rate, are the primary indicators of thermal stress. Under a stressed environment temperature humidity index (THI) had established as a vital measurement to identify the thermal stress in livestock. THI in association with climatic variations can define the environmental effect as stressful or comfortable for livestock. Goats are small ruminants that adapt to a wide range of ecological variations due to their anatomical and physiological characteristics. However, the productivity of animals declines at the individual level during thermal stress. Stress tolerance can be determined through genetic studies associated with at the cellular level using physiological as well as molecular approaches. Information on genetic association with thermal stress in goats is scanty, this severely affects their survival and hence productivity of livestock. The ever-increasing demand for food across the globe needs deciphering novel molecular markers as well as stress indicators that play a vital role in livestock improvement. This review represents an analysis of current knowledge of phenotypic differences during thermal stress and signifies the importance of physiological responses and their association at the cellular level in goats. The regulation of vital genes associated with thermal stress such as Aquaporins (AQP 0, 1, 2, 4, 5, 6, 8), aquaglyceroporins (AQP3, 7, 9, and 10) and super-aquaporins (AQP 11, 12); BAX inhibitors such as PERK (PKR like ER kinase), IRE 1(inositol-requiring-1); Redox regulating genes such as NOX; Transport of Na+ and K+ such as ATPase (ATP1A1) and several heat shock proteins have been implicated in heat-stress related adaptations have been elucidated. As these changes have a significant impact on production performance as well as on livestock productivity. Such efforts may help in the development of molecular markers and will assist the breeders to develop heat-tolerant goats with improved productivity.

Effects of diets differing in dietary cation-anion difference and calcium concentration on calcium homeostasis in neutered male sheep

Feeding low dietary cation-anion difference (DCAD) diets is one strategy to prevent milk fever in cows. The mechanism of action, as well as whether the calcium (Ca) supply of such diets combined with this feeding regimen should meet the requirements, is still unclear. Small ruminants are commonly used as models for cows. The goal of the present study was to demonstrate basic effects of DCAD against a background of different Ca supplies in a sheep model. Twenty-three castrated male East Friesian milk sheep, aged 11 to 12 mo, were randomly assigned to 4 different feeding groups. The ration of each group was either high (highDCAD) or low in DCAD (lowDCAD) combined with adequate (nCa) or restricted Ca supply (lowCa). At baseline, serum and urine were collected from all sheep and a peripheral quantitative computed tomography of the left metatarsus was performed. After a 14-d adaptation period to the different diets, the experiment started (d 0). Urine, feces, and serum were collected on d 0, 4, 7, 14, and 22, and peripheral quantitative computed tomography was performed on d 0 and 22. On d 22, the sheep were killed and sampled for functional studies. LowDCAD was significantly associated with lower urine pH, higher urinary Ca excretion, higher ionized Ca in blood, and higher serum Ca concentrations. Blood pH and bone parameters did not differ significantly between groups. It is unclear from which compartment the high amounts of Ca excreted with urine in the lowDCAD groups originated. Interestingly, lowDCAD resulted in higher renal mRNA abundance of parathyroid hormone receptor but unaffected mRNA abundance of Ca transporters. As neither renal abundance of these transporters nor Ca excretion were influenced by dietary Ca supply, our results support the hypothesis that increased urinary Ca observed with low DCAD diets represents a loss rather than an excretion of surplus Ca.

Differences between Holstein dairy cows in renal clearance rate of urea affect milk urea concentration and the relationship between milk urea and urinary nitrogen excretion

Urine and fecal excretions from cattle contribute to global nitrogen (N) emissions. The milk urea nitrogen (MUN) concentration in dairy cows is positively correlated with urinary urea N (UUN) emissions, and both decline with the reduction in crude protein intake. However, MUN concentration may differ between individual cows despite feeding the same ration. Thus, we hypothesized that due to differences in endogenous N utilization cows with high MUN concentration excrete more UUN than cows with a low MUN concentration. The objective of the present study was to elucidate N partitioning and urea metabolism in dairy cows with divergent MUN concentrations fed two planes of crude protein. Twenty Holstein dairy cows with high (HMU; n = 10) and low (LMU; n = 10) milk urea concentrations were fed two isocaloric diets with a low (LP) and normal (NP) crude protein level. Methane and ammonia emissions were recorded in respiration chambers. Feed intake, feces and urine excretions and milk yield were recorded for four days and subsamples were analyzed for total N and N-metabolites. A carbon-13 labeled urea bolus was administered intravenously followed by a series of plasma samplings. Total N and UUN excretions and ammonia emissions from excreta were lower on the LP diet, however, methane emissions, urinary N excretions and ammonia emissions were comparable between groups. Although plasma and salivary urea concentrations, urea pool size and urea turnover were higher, HMU cows had lower renal urea clearance rates. Additionally, HMU cows had lower renal clearance rates for creatinine, uric acid and creatine and excreted less uric acid (on the LP diet only) and creatine with urine. In conclusion, contrary to our hypothesis, HMU cows did not excrete more UUN than LMU cows. The lower urinary creatine excretion of HMU cows suggests that these animals have a lower environmental nitrogen footprint.

Dietary phosphorus restriction affects bone metabolism, vitamin D metabolism and rumen fermentation traits in sheep

Homeostasis of calcium (Ca) and phosphate (P_i ) is maintained by a concerted interplay of absorption and reabsorption via the gastrointestinal tract and the kidney and by storage and mobilization from the bone regulated mainly by parathyroid hormone (PTH), 1,25-dihydroxycholecalciferol and calcitonin. The present study aimed at characterizing the effects of dietary P restriction on bone, vitamin D metabolism and rumen fermentation traits reflecting the endogenous P cycle maintaining the ruminal P supply for microbial metabolism. The experiments were done in eleven female, non-pregnant, non-lactating four- to nine-year-old Black Headed Mutton sheep allotted to two feeding groups: "P-restricted" (0.11% P/kg DM and 0.88% Ca/kg DM) and "Control" (0.38% P/kg DM and 0.88% Ca/kg DM). Dietary P restriction did not lead to hypophosphataemia, probably due to a compensation by bone mobilization, demonstrated by increased serum concentrations of a resorption marker and altered gene expression in bone tissue. In addition, the RNA expression of fibroblast growth factor 23, a bone-derived factor involved in the regulation of vitamin D metabolism, was significantly reduced with dietary P restriction. Furthermore, several genes related to vitamin D metabolism and plasma concentrations of 1,25-(OH)₂ D were associated with serum concentrations of phosphate (P_i ). In the parotid gland, the expression of the P_i transporter NaPi2b was negatively associated with serum P_i and positively with parathyroid PTH expression. Although P_i concentrations in saliva and the gastrointestinal tract were significantly reduced, we found no adverse effects of the P-restricted ration on the production of short chain fatty acids, but slight differences in the production of butyrate as well as its relationship to rumen P_i and ammonia concentrations that might indicate an impact on ruminal fermentation.

Dietary protein and calcium modulate parathyroid vitamin D receptor expression in young ruminants

For economic reasons and in order to minimize nitrogen excretion and thus pollution, the crude protein content in the diet of livestock animals should be as low as possible without negatively affecting the animals´ health and performance. As ruminants can efficiently use dietary protein because of the ruminohepatic circulation of urea, they are considered to cope more easily with such a feeding regime than monogastric animals. However, despite unaltered daily weight gain, massive changes in mineral homeostasis and vitamin D metabolism were observed with dietary protein reduction (N-) in young, growing goats. Serum concentrations of 1,25-dihydroxyvitamin D₃ (1,25-(OH)₂D₃) were decreased with a low N intake, even if calcium (Ca) was also restricted (Ca-). Interestingly, concentrations of cyclic adenosine monophosphate (cAMP) measured as an indirect assessment for the parathyroid hormone (PTH) activity were not affected by low protein. Therefore, it was hypothesized that the sensitivity of the parathyroid gland is modulated during these dietary interventions. Four groups of male German colored goats received a control (N+/Ca+), a reduced protein (N-/Ca+), a reduced Ca (N+/Ca-) or a reduced protein and Ca (N-/Ca-) diet. After six weeks we determined the expression of PTH, PTH receptor, Ca sensing receptor (CASR), vitamin D receptor (VDR), retinoid X receptor (RXRα), Klotho, fibroblast growth factor receptor 1c-splicing form, and the sodium-dependent P_i transporter (PiT1) in the parathyroid glands. Concentrations of cAMP were not affected, while those of Ca and 1,25-(OH)₂D₃were diminished and that of 25-hydroxyvitamin D₃ was increased with N- feeding. The expression patterns of the described target genes were not altered. In contrast, animals fed the Ca- rations showed enhanced serum 1,25-(OH)₂D₃ and cAMP levels with no changes in blood Ca concentrations demonstrating an efficient adaptation. The mRNA expression of expression of VDR and CASR in the parathyroid gland was significantly diminished and RXRα, PTHR and PiT1 expression was elevated. Instead of the assumed desensitization of the parathyroid gland with N-, our results indicate elevated responsiveness to decreased blood Ca with feeding Ca-.

Modulation of growth hormone receptor-insulin-like growth factor 1 axis by dietary protein in young ruminants

A reduced protein intake causes a decrease in insulin-like growth factor 1 (IGF1) concentrations and modulates Ca homoeostasis in young goats. IGF1 is synthesised by the liver in response to stimulation by growth hormone (GH). Due to rumino-hepatic circulation of urea, ruminants are suitable for investigating the effects of protein reduction despite sufficient energy intake. The present study aimed to investigate the impact of a protein-reduced diet on the expression of components of the somatotropic axis. Male young goats were divided into two feeding groups receiving either a control diet (20 % crude protein (CP)) or a reduced-protein diet (9 % CP). Blood concentrations of IGF1 and GH were measured, and a 24-h GH secretion profile was compiled. Moreover, ionised Ca and insulin concentrations as well as mRNA and protein expression levels of hepatic proteins involved in GH signalling were quantified. Due to the protein-reduced diet, concentrations of ionised Ca, insulin and IGF1 decreased significantly, whereas GH concentrations remained unchanged. Expression levels of the hepatic GH receptor (GHR) decreased during protein reduction. GHR expression was down-regulated due to diminished insulin concentrations as both parameters were positively correlated. Insulin itself might be reduced due to reduced blood Ca levels that are involved in insulin release. The protein-reduced diet had an impact on the expression of components of the somatotropic axis as a disruption of the GH–IGF1 axis brought about by diminished GHR expression was shown in response to a protein-reduced diet.

Modulation of renal calcium and phosphate transporting proteins by dietary nitrogen and/or calcium in young goats

In young goats, a reduction in dietary nitrogen (N) had an impact on mineral homeostasis although ruminants are able to recycle N effectively due to rumino-hepatic circulation. A solitary calcium (Ca) reduction stimulated calcitriol synthesis and Ca concentrations remained unchanged, whereas a dietary N reduction led to a decrease in calcitriol, which could not be prevented by a simultaneous reduction of N and Ca. In a previous study, it was shown that a reduced dietary N intake caused a decrease in intestinal Ca absorption due to a reduction of intestinal Ca transporting proteins. As no data on the potential role of the kidneys are available, it was the aim of the present study to evaluate whether an N- and/or Ca-reduced diet had an impact on renal Ca and phosphate (Pi) transporting protein expression in young goats. The animals were divided into 4 feeding groups, each receiving an adequate N and Ca supply, a reduced N supply, a reduced Ca supply, or a combined N and Ca reduction for 6 to 9 wk. The protein expression of the renal Ca channel transient receptor potential cation channel subfamily V member 5 (TRPV5) was diminished in N-reduced fed goats (P = 0.03), whereas in Ca restricted animals, the expression remained unaltered. The mRNA and protein expression of the Ca-binding protein calbindin-D28K (CaBPD28K) and the sodium-Ca exchanger 1 (NCX1) were significantly decreased due to the N-reduced feeding (mRNA, P = 0.003; P < 0.0001; protein, P = 0.002; P = 0.02), whereas dietary Ca reduction increased the CaBPD28K and NCX1 mRNA expression (P = 0.05; P = 0.01). The mRNA and protein expression of the parathyroid hormone receptor (PTHR) decreased due to the N-reduced feeding (P = 0.02; P = 0.03). These results confirm that a reduced dietary N intake led to decreased TRPV5, CaBPD28K, PTHR, and NCX1 expression levels, contributing to low levels of calcitriol and plasma Ca. In contrast to this, sodium-phosphate cotransporter type IIa expression and plasma Pi concentration were increased during dietary N reduction, thus indicating that Pi homeostasis is modulated in a calcitriol-independent manner. In conclusion, the modulation of Ca transporting proteins expression in the kidney is not able to prevent changes in mineral homeostasis in young goats receiving an N-reduced diet.

Dietary nitrogen and calcium modulate CYP27B1 expression in young goats

In livestock, feeding a reduced nitrogen (N) diet is favored for economic and ecological reasons. Ruminants cope more easily with a reduced N diet than monogastric species. However, changes in mineral homeostasis such as a reduction in 1,25-dihydroxyvitamin D₃ (1,25-(OH)₂D₃) concentrations, calcium (Ca), and IGF1 levels were observed in goats kept on a reduced N diet. The decrease in 1,25-(OH)₂D₃ occurred even during a simultaneous reduction in dietary N and Ca, whereas a solitary Ca reduction stimulated 1,25-(OH)₂D₃ synthesis. The aim of the present study was to examine the effects of N- and/or Ca-reduced diets on the expression of 24-hydroxylase (CYP24A1), 1-alpha-hydroxylase (CYP27B1), vitamin D receptor (VDR), retinoid X receptor alpha (RXRα), IGF1 receptor (IGF1R), Klotho, and fibroblast growth factor receptor 1c (FGFR1c) in kidneys of young goats. Four groups were kept on a control diet, an N-reduced diet, a Ca-reduced diet or an N- and a Ca-reduced diet. Renal expression of CYP24A1 was not affected, whereas CYP27B1 expression was significantly diminished in the N-reduced diet fed goats (P < 0.05) and significantly elevated with the Ca reduction (P < 0.001). The VDR expression was not modified, whereas RXRα (P < 0.05) and Klotho expression (P < 0.001) were stimulated during Ca reduction. The IGF1R (P < 0.05) and FGFR1c (P < 0.05) expression were enhanced with the N reduction. From these data, it can be concluded that the downregulation of renal CYP27B1 expression observed with dietary N reduction is probably mediated by a complex interaction between the somatotropic axis and the Klotho/FGF signaling pathway in young goats.

Urine Ammonium, Metabolic Acidosis and Progression of Chronic Kidney Disease

The metabolism of a typical Western diet generates 50-100 mEq of acid (H+) per day, which must be excreted in the urine for the systemic acid-base to remain in balance. The 2 major mechanisms that are responsible for the renal elimination of daily acid under normal conditions are ammonium (NH4+) excretion and titratable acidity. In the presence of systemic acidosis, ammonium excretion is intensified and becomes the crucial mechanism for the elimination of acid. The impairment in NH4+ excretion is therefore associated with reduced acid excretion, which causes excess accumulation of acid in the body and consequently results in metabolic acidosis. Chronic kidney disease (CKD) is associated with the impairment in acid excretion and precipitation of metabolic acidosis, which has an adverse effect on the progression of CKD. Recent studies suggest that the progressive decline in renal ammonium excretion in CKD is an important determinant of the ensuing systemic metabolic acidosis and is an independent factor for predicting the worsening of kidney function. While these studies have been primarily performed in hypertensive individuals with CKD, a closer look at renal NH4+ excretion in non-hypertensive individuals with CKD is warranted to ascertain its role in the progression of kidney disease.

Phenotypic homogeneity with minor deviance in osmotic fragility of Sahel goat erythrocytes in non-ionic sucrose media during various physiologic states

BACKGROUND

Erythrocyte swelling in non-ionic sucrose media and the subsequent osmotic lysis are influenced by mechanisms of regulatory volume adjustment and osmotic water permeability. Kinetics of transmembrane water and ion fluxes in varied physiologic states may determine the phenotype of erythrocyte osmotic fragility (EOF) and affect estimates of EOF.

METHODS

Effects of sex, age, late pregnancy (third trimester) and lactation on the haemolysis of Sahel goat erythrocytes incubated in a series of hyposmotic non-ionic sucrose media were investigated.

RESULTS

The fragiligram was sigmoidal in 72 (97%) out of 74 goats. Two male (3%) goats with low and high extreme median erythrocyte fragilities (MEF), had non-sigmoidal curves. The mean fragilities at osmolarities of 30-300 mosmol/L of sucrose and the mean osmolarities responsible for 10%-90% haemolysis (CH10-CH90) were not significantly different between males and non-pregnant dry (NPD) females, amongst the age groups and between pregnant or lactating and NPD female goats. The MEF (CH50) of the goats were at osmolarities of 126-252 mosmol/L (median of data: 171 mosmol/L) with a mean of 175.24±16.20 mosmol/L. Therefore, phenotypic homogeneity of EOF occurred with minor deviance, since EOF variables were not differentiated by sex, age, late pregnancy or lactation.

CONCLUSIONS

Physiologic states of the goat did not affect EOF phenotype in non-ionic sucrose media. Sigmoidal fragility phenotype seemed to be homogeneously conserved by osmoregulatory mechanisms not partitioned by sex, age, late pregnancy or lactation, but a minor non-sigmoidal curve might have occurred due to altered erythrocyte osmotic behaviour that would require further investigation.

Modulation of intestinal calcium and phosphate transport in young goats fed a nitrogen- and/or calcium-reduced diet

Feeding ruminants a reduced N diet is a common approach to reduce N output based on rumino-hepatic circulation. However, a reduction in N intake caused massive changes in Ca and inorganic phosphate (Pi) homoeostasis in goats. Although a single dietary Ca reduction stimulated intestinal Ca absorption in a calcitriol-dependent manner, a concomitant reduction of Ca and N supply led to a decrease in calcitriol, and therefore a modulation of intestinal Ca and Pi absorption. The aim of this study was to examine the potential effects of dietary N or Ca reduction separately on intestinal Ca and Pi transport in young goats. Animals were allocated to a control, N-reduced, Ca-reduced or combined N- and Ca-reduced diet for about 6-8 weeks, whereby N content was reduced by 25 % compared with recommendations. In Ussing chamber experiments, intestinal Ca flux rates significantly decreased in goats fed a reduced N diet, whereas Pi flux rates were unaffected. In contrast, a dietary Ca reduction stimulated Ca flux rates and decreased Pi flux rates. The combined dietary N and Ca reduction withdrew the stimulating effect of dietary Ca reduction on Ca flux rates. The expression of Ca-transporting proteins decreased with a reduced N diet too, whereas Pi-transporting proteins were unaffected. In conclusion, a dietary N reduction decreased intestinal Ca transport by diminishing Ca-transporting proteins, which became clear during simultaneous N and Ca reduction. Therefore, N supply in young ruminant nutrition is of special concern for intestinal Ca transport.