Khalid A. Abdoun

Ammonia and urea transport across the rumen epithelium: a review

The transport of nitrogen across the rumen epithelium is characterized by absorption of ammonia from the rumen and by an influx of urea into the rumen. The transport rates of both compounds are large and exhibit wide variation. The transport of ammonia occurs in two forms: in the lipophilic form as NH3, the magnitude of which is linearly related to the pH in the ruminal fluid at pH values above 7, while at a physiological pH of 6.5 or lower, ammonia is predominantly absorbed as NH4+ via putative potassium channels in the apical membrane. The uptake of NH4+ depends on the potential difference of the apical membrane, Pda, and shows competition with K uptake. The pathway for basolateral exit of NH4+ is unknown. Hence, the relative transport rates of NH3 or NH4+ are determined by the ruminal pH according to the Henderson–Hasselbalch equation. Transport of ammonia interacts with the transport of Na and Mg mainly via changes of the intracellular pH. Urea recycling into the rumen has been known for many years and the transport across the rumen epithelium is mediated via urea transporters in the luminal and basolateral membrane of the epithelium. Transport of urea occurs by simple diffusion, but is highly variable. A significant increase of urea influx is caused by the fermentation products CO2 and short-chain fatty acids. Conversely, there is some evidence of inhibition of urea influx by ruminal ammonia. The underlying mechanisms of this modulation of urea transport are unknown, but of considerable nutritional importance, and future research should be directed to this aspect of ruminal transport.

Modulation of urea transport across sheep rumen epithelium in vitro by SCFA and CO2

Urea transport across the gastrointestinal tract involves transporters of the urea transporter-B group, the regulation of which is poorly understood. The classical stimulatory effect of CO(2) and the effect of short-chain fatty acids (SCFA) on the ruminal recycling of urea were investigated by using Ussing chamber and microelectrode techniques with isolated ruminal epithelium of sheep. The flux of urea was found to be phloretin sensitive and passive. At a luminal pH of 6.4, but not at 7.4, the addition of SCFA (40 mmol/l) or CO(2)/HCO3- (10% and 25 mmol/l) led to a fourfold increase in urea flux. The stepwise reduction of luminal pH in the presence of SCFA from 7.4 to 5.4 led to a bell-shaped modification of urea transport, with a maximum at pH 6.2. Lowering the pH in the absence of SCFA or CO(2) had no effect. Inhibition of Na(+)/H(+) exchange increased urea flux at pH 7.4, with a decrease being seen at pH 6.4. In experiments with double-barreled, pH-sensitive microelectrodes, we confirmed the presence of an apical pH microclimate and demonstrated the acidifying effects of SCFA on the underlying epithelium. We confirm that the permeability of the ruminal epithelium to urea involves a phloretin-sensitive pathway. We present clear evidence for the regulation of urea transport by strategies that alter intracellular pH, with permeability being highest after a moderate decrease. The well-known postprandial stimulation of urea transport to the rumen in vivo may involve acute pH-dependent effects of intraruminal SCFA and CO(2) on the function of existing urea transporters.

Modulation of sheep ruminal urea transport by ammonia and pH

Ruminal fermentation products such as short-chain fatty acids (SCFA) and CO2 acutely stimulate urea transport across the ruminal epithelium in vivo, whereas ammonia has inhibitory effects. Uptake and signaling pathways remain obscure. The ruminal expression of SLC14a1 (UT-B) was studied using polymerase chain reaction (PCR). The functional short-term effects of ammonia on cytosolic pH (pHi) and ruminal urea transport across native epithelia were investigated using pH-sensitive microelectrodes and via flux measurements in Ussing chambers. Two variants (UT-B1 and UT-B2) could be fully sequenced from ovine ruminal cDNA. Functionally, transport was passive and modulated by luminal pH in the presence of SCFA and CO2, rising in response to luminal acidification to a peak value at pH 5.8 and dropping with further acidification, resulting in a bell-shaped curve. Presence of ammonia reduced the amplitude, but not the shape of the relationship between urea flux and pH, so that urea flux remained maximal at pH 5.8. Effects of ammonia were concentration dependent, with saturation at 5 mmol/l. Clamping the transepithelial potential altered the inhibitory potential of ammonia on urea flux. Ammonia depolarized the apical membrane and acidified pHi, suggesting that, at physiological pH (< 7), uptake of NH4 (+) into the cytosol may be a key signaling event regulating ruminal urea transport. We conclude that transport of urea across the ruminal epithelium involves proteins subject to rapid modulation by manipulations that alter pHi and the cytosolic concentration of NH4 (+). Implications for epithelial and ruminal homeostasis are discussed.

Concerns about Misinterpretation of Recent Scientific Data Implicating Dromedary Camels in Epidemiology of Middle East Respiratory Syndrome (MERS)

This letter addresses some concerns about two recent articles published by the same authors in mBio (1, 2), specifically many uncertainties regarding the potential applicability of their epidemiological data, which were obtained from dromedary camels (DCs) infected with Middle East respiratory syndrome coronavirus (MERS-CoV), to human public health. Aiming to investigate the possible role of DCs in the transmission of MERS-CoV to humans, the authors in their first article determined the seroprevalence of MERS-CoV infection in DCs throughout Saudi Arabia and arrived at three main conclusions (1). Their first conclusion was that DCs can be infected with MERS-CoV, as evident by the determination of (i) high loads of viral nucleic acids (RNA) and antibodies to MERS-CoV in archived and freshly collected samples and (ii) a high resemblance (>99%) in the collected samples in three regions of phylogenetically analyzed MERS-CoV genomic sequence. Their second conclusion is that there are seroprevalence differences in MERS-CoV infection depending on the camel’s age (95% of the adults compared to 35% of the juveniles) and the region of the country (ranging from 90% in the East to 5% in the Southwest). The third conclusion is that airborne transmission is the main mode of MERS-CoV transmission, as evidenced by the more frequent detection of viral nucleic acids in nasal swabs than in rectal specimens. Furthermore, the authors in their second article described complete genomic sequencing of MERS-CoV isolated from both DCs and humans and arrived at two more conclusions (2). First, they demonstrated that DCs can be simultaneously infected with three genetic variants (genotypes) of MERS-CoV; second, they showed that the alignment of the complete genomic sequence of one MERS-CoV genotype (claimed to be a quasispecies) obtained from culturing the virus from nasal swab samples of DCs was indistinguishable from the genomic sequence of MERS-CoV recovered …

Effects of dietary seaweed (Ulva lactuca) supplementation on the reproductive performance of buck and doe rabbits

The aim of this study was to investigate the effect of dietary supplementation of seaweed on the reproductive performance of rabbits. Two trials were performed during this study. In the first trial, semen quality was evaluated in 15 buck rabbits with mean body weight of 4.80±0.41 kg and six month of age. In the second trial, prolificacy was determined in 30 artificially inseminated does with a mean body weight of 4.84±0.50 kg and five to six months of age. Rabbits in each trial were randomly allocated to one of three dietary seaweed levels; commercial pelleted diet (C), pelleted diet supplemented with 1% seaweed (T1), and pelleted diet supplemented with 2% seaweed (T2). Dietary supplementation of seaweed significantly increased plasma testosterone concentration and improved various sperm motility parameters. Analysis of acrosomal membrane integrity using electron microscopy revealed no significant influences of dietary seaweed supplementation on quality grade (I–IV) of all tested samples. These results reflected in positive prolificacy response of does artificially inseminated with semen samples pooled from bucks fed on T2, and offered diet supplemented with 2% seaweed one week prior to their insemination and throughout the gestation period. Feeding diets supplemented with 2% seaweed to doe rabbits improved their kindling rate, litter size, and their offspring ratio. Seaweed supplementation to the diets of rabbits raised under summer conditions had improved their reproductive performance by improving the semen fertility characteristics of bucks and the prolificacy characteristics of does. Hematological and biochemical parameters investigated in this study did not reveal any pathological signs in both rabbits genders due to dietary seaweed supplementation.

Regional and circadian variations of sweating rate and body surface temperature in camels (Camelus dromedarius).

It was the aim of this study to investigate the regional variations in surface temperature and sweating rate and to visualize body thermal windows responsible for the dissipation of excess body heat in dromedary camels. This study was conducted on five dromedary camels with mean body weight of 450 ± 20.5 kg and 2 years of age. Sweating rate, skin and body surface temperature showed significant (P < 0.001) circadian variation together with the variation in ambient temperature. However, daily mean values of sweating rate, skin and body surface temperature measured on seven regions of the camel body did not significantly differ. The variation in body surface temperature compared to the variation in skin temperature was higher in the hump compared to the axillary and flank regions, indicating the significance of camels fur in protecting the skin from daily variation in ambient temperature. Infrared thermography revealed that flank and axillary regions had lower thermal gradients at higher ambient temperature (T(a) ) and higher thermal gradients at lower T(a) , which might indicate the working of flank and axillary regions as thermal windows dissipating heat during the night. Sweating rate showed moderate correlation to skin and body surface temperatures, which might indicate their working as potential thermal drivers of sweating in camels.

Dietary inclusion of chromium to improve growth performance and immune-competence of broilers under heat stress

This study was conducted to investigate the effects of dietary supplementation with chromium chloride, CrCl3.6H2O (2mg kg–1 basal diet) on the performance and immune response of broiler chickens under heat stress condition (25-43°C). A total of 80 one-day-old broiler chicks (Ross-308) were assigned to two treatment groups according to a completely randomized design. Each treatment consisted of four equal replicates, each contained ten chicks. Chicks were fed on basal diets supplemented with different concentrations of chromium (0 and 2 mg kg–1 CrCl3) from 1 to 35 days of age. Chromium supplementation as feed additives resulted in a slightly lower rectal temperature, and significantly (P<0.05) lower respiration rate for the broiler chickens received diet supplemented with chromium compared to the control (0 mg kg–1 CrCl3). Dietary chromium supplementation increased final body weight (BW) at the end of the production period (5 weeks). Average weight gain was significantly (P<0.05) higher in chickens fed on chromium supplemented diet. Feed intake was not influenced by dietary chromium supplementation, however, the efficiency of feed conversion was improved (P<0.05) in chromium supplemented chickens. Furthermore, dressing percentage was significantly (P<0.05) higher in Cr-treated chickens compared to control chickens. Chromium supplementation significantly (P<0.05) improved the immune response to Newcastle Disease Virus vaccine (NDV). The present results suggest that dietary chromium supplementation provides a good nutritional management approach to ameliorate heat stress induced depression in production performance and immune response of broiler chickens.

Daily Rhythms of Physiological Parameters in the Dromedary Camel Under Natural and Laboratory Conditions

Camels are well adapted to hot arid environments and can contribute significantly to the economy of developing countries in arid regions of the world. Full understanding of the physiology of camels requires understanding of the internal temporal order of the body, as reflected in daily or circadian rhythms. In the current study, we investigated the daily rhythmicity of 20 physiological variables in camels exposed to natural oscillations of ambient temperature in a desert environment and compared the daily temporal courses of the variables. We also studied the rhythm of core body temperature under experimental conditions with constant ambient temperature in the presence and absence of a light-dark cycle. The obtained results indicated that different physiological variables exhibit different degrees of daily rhythmicity and reach their daily peaks at different times of the day, starting with plasma cholesterol, which peaks 24min after midnight, and ending with plasma calcium, which peaks 3h before midnight. Furthermore, the rhythm of core body temperature persisted in the absence of environmental rhythmicity, thus confirming its endogenous nature. The observed delay in the acrophase of core body temperature rhythm under constant conditions suggests that the circadian period is longer than 24h. Further studies with more refined experimental manipulation of different variables are needed to fully elucidate the causal network of circadian rhythms in dromedary camels.

Correlation of blood triiodothyronine (T3) level with some production traits in male goat kids

Khalid ABDOUN*, Emad SAMARA, Aly OKAB, Mohamed AL-BADWI, Mohamed EL-ZAREI, Ali AL-SEAF, Ahmed AL-HAIDARY Department of Animal Production, College of Food and Agriculture Sciences, King Saud University, Riyadh, Saudi Arabia Department of Environmental Studies, Institute of Graduate Studies and Research, Alexandria University, Alexandria, Egypt Department of Animal Production and Breeding, College of Agriculture and Veterinary Medicine, Qassim University, Qassim, Saudi Arabia

Assessment of heat tolerance and production performance of Aardi, Damascus, and their crossbred goats

The question of whether the adaptability and production performance in goats may be enhanced using a crossbreeding program between bucks of a native and heat-tolerant breed and does of an exotic and dual-purpose breed was approached and examined herein by comparing purebred Aardi and Damascus goats and their crossbred lines (i.e., 1/2 Aardi 1/2 Damascus (½A½D) and 1/4 Aardi 3/4 Damascus (¼A¾D)) reared in a region characterized by dry and hot bioclimatic conditions. Twenty-four male 6-month-old kids randomly segregated into four groups (six replicates/group) were used for the experiment. Climatic, thermo-physiological, biophysiological, metabolic, blood hematological, and biochemical measurements were all determined. The obtained results indicated that such a program was proven to be successful. This conclusion was demonstrated by the findings that crossbred goats (i.e., 1/2A1/2D and 1/4A3/4D) under such bioclimatic conditions were able to show (P < 0.05) higher heat tolerance capabilities compared to purebred Damascus goats as well as manifested (P < 0.05) higher production performance compared to the purebred Aardi goats. Accordingly, these evidences could emphasize that the crossbreeding may enable these animals to display a simultaneous improvement of both traits by the possible benefits that could arise from heterosis and breed complementarity. Researches dealing with this aspect may very well improve our understanding of goat’s production and welfare under harsh environmental conditions. Future studies should include an economic analysis of traits that have the potential to impact the overall profitability to a vertically coordinated system.