The aim of the present study was to synthesize a photocatalyst on the basis of TiO2 with kaolin as the support material. Properties such as layered structure and a suitable particle size of kaolin could be beneficial in the production of a high-quality and relatively cheap photocatalyst on an industrial scale. Homogeneous hydrolysis with urea as a precipitation agent and kaolin as support material was used to obtain a kaolin surface covered with TiO2. Samples were characterized by means of X-ray powder diffraction, infrared and Raman spectroscopy, high-resolution transmission electron microscopy, Brunauer-Emmett-Teller surface area, and Barrett-Joyner-Halenda porosity determination. Photocatalytic activity was assessed by a Reactive Black 5 azo dye discoloration in a water suspension and by acetone decomposition on a thin layer of sample in a gas phase. The characterization confirmed that the well crystallized TiO2 was distributed effectively over the whole surface of a kaolin substrate, and photocatalytic tests revealed that the active surface layer of titania particles on kaolin performed well, suggesting that kaolin acts as a suitable support.

This study evaluated the effect of replacing soybean meal by a blend of ground corn and urea-ammonium sulphate (GCU-S) in the diet of lactating buffaloes on milk production and composition, digestibility, N balance and blood metabolites. Twelve multiparous dairy Murrah buffaloes (Bubalus bubalis), at 100 ± 4 d in milk and yielding 10 ± 2.5 kg/d, were randomly distributed in a triple 4 × 4 Latin square, with four different inclusions of GCU-S at U-S levels: 0 (control), 8.0, 16.4 and 24.1 g/kg dry matter (DM) total. Replacing soybean meal with GC-US had a significant depressing effect on absolute DM intake, which was still numerically evident but no longer significant when expressed on a body weight-related basis. Intakes of crude protein (CP) and N as well as N-urinary excretion were also significantly depressed. Digestibility of dry matter was improved and, as a proportion of DMI, intake of total digestible nutrients increased significantly. Perhaps as a result, feed efficiency (kg DMI required per kg 6% fat-corrected milk) was significantly improved. Efficiency of protein use for milk production was significantly improved, but not when expressed as milk protein output. N transfer into milk, as a proportion of total N intake, also increased significantly. However, GC-US inclusion had no significant effect on milk production or milk composition, nor did it affect serum metabolites, digestibilities (apart from dry matter) or N measures of balance apart from those mentioned above. Inclusion of this blend of ground corn with urea and ammonium suplate can be recommended for dairy buffalo because, although it decreases DMI and N-excretion, it improves DM digestibility and feeding efficiency whilst maintaining milk production and composition.

The objective of this study was to evaluate the fermentative characteristics and chemical composition of cochineal nopal cactus silage additives with urea or Lactobacillus buchneri (LB), as well as the association of both additives in four storage times (7, 15, 60 and 120 days) and during aerobic stability, with evaluations at 0, 48 and 96 h. Four silages were used: no additive, addition of 2% urea, addition of LB and addition of 2% urea and LB. The study was divided into two experiments: the first experiment evaluated the silages at different storage times, and the second experiment evaluated the silages during the aerobic stability test. In both experiments, the experimental design was completely randomized in a factorial scheme (4 × 4 and 4 × 3) with three replicates per treatment. After the ensiling process, lactic acid bacteria predominated in all treatments. The concentration of lactic acid increased significantly from 60 days of ensiling. The concentration of acetic acid varied significantly between the storage times only for the silages treated with urea and LB alone. The silage treated with urea maintained a constant pH value up to 120 days of storage. During the 96 h aerobic stability test, no breaking in the stability of silages was observed. The exclusive or associated use of urea and LB promotes improvement in the fermentative characteristics of cochineal nopal cactus silage, without major alterations in the chemical composition or interfering with the aerobic stability of the silages.

Off-target paraquat movement to rice has become a major problem in recent years for rice producers in the midsouthern United States. Nitrogen (N) fertilizer is applied to rice in greater quantity and frequency than all other nutrients to optimize rice yield. Two separate field studies were conducted from 2015 to 2018 in Stoneville, MS, to assess whether starter N fertilizer can aid rice recovery from exposure to a sub-lethal concentration of paraquat and to evaluate rice response to different N fertilizer management strategies following exposure to a sub-lethal concentration of paraquat. In both studies, paraquat treatments consisted of paraquat at 0 and 84 g ai ha–1 applied to rice in the two- to three-leaf (EPOST) growth stage. In the starter fertilizer study, N fertilizer at 24 kg ha–1 as ammonium sulfate (AMS) was applied to rice at spiking- to one-leaf (VEPOST), two- to three-leaf (EPOST), or three- to four-leaf (MPOST) growth stages before and after paraquat treatment. In the N fertilizer timing study, N fertilizer at 168 kg N ha–1 was applied in a single four-leaf to one-tiller (LPOST) application or two-, three-, and two four-way split applications. Despite starter N fertilizer applications, paraquat injured rice ≥41%, reduced height 57%, reduced dry weight prior to flooding 77%, delayed maturity 10 d, reduced dry weight at maturity 33%, and reduced rough rice yield 35% in the starter fertilizer study. Similarly, in the N fertilizer timing study, paraquat injured rice ≥45%, reduced height 14%, delayed maturity 10 d, reduced dry weight at maturity 44%, and reduced rough rice yield 50% for all N fertilizer management strategies. Both studies indicate that severe complications in growth and development can occur from rice exposure to a sub-lethal concentration of paraquat. In both studies, manipulation of N fertilizer management did not facilitate rice recovery from early-season exposure to paraquat.

Using legumes in forage mixes can help decrease the use of nitrogen fertilizers and possibly increase the nutritive value of pasture. The aim of the current study was to determine animal production and behavioural and ingestion parameters by evaluating the production and nutritive value of Aruana grass (Panicum maximum ‘Aruana’) intercropped with forage peanut (Arachis pintoi ‘Amarillo’) or fertilized with nitrogen. The treatments were N200 (200 kg N/ha per season – summer and winter), 100N + PE (100 kg N/ha per season plus pasture mixture with forage peanut) and N100 (100 kg N/ha per season). The presence of forage peanut in the pasture did not replace nitrogen fertilization as the pasture fertilized with 200 kg of nitrogen had a greater leaf/stem ratio (0.66 v. 0.54), stocking rate (2600 v. 2290 kg live weight/ha), average daily gain (0.880 v. 0.700 kg/day) and live weight gain (LWG) (652 v. 468 kg/ha) during summer. During winter, no effect of increased nitrogen fertilization on pasture and animal production was observed. In the total study period (summer + winter), a greater LWG (897 v. 741 kg/ha) occurred when a higher quantity of nitrogen (N200) was placed in the pasture compared to the insertion of forage peanuts in the system.

A well-balanced amino acid profile in the feedstuffs for livestock is essential to support adequate growth. This is well studied for monogastric species but still not well understood for ruminants and especially for the most unconventional species, like cervids. This study investigated the influence of ruminally protected lysine (Lys) and methionine (Met) supplementation during the fattening period, as well as two slaughter seasons (late autumn (LA) v. late winter (LW)), on the growth, carcass traits, body condition and blood plasma metabolites of fallow deer (Dama dama). Forty-five yearlings of fallow deer bucks were allocated into three groups, balanced by weight (40.2 ± 2.7 kg). The deer were pasture-fed and supplemented with barley, free-choice mineral premix, silage during the winter period, and varying levels of ruminally protected Lys and Met: no amino acids (Control), 9 g/day of Lys, and 9 g/day of Lys plus 3 g/day of Met (Lys+Met). Animals were slaughtered in two separate seasons, LA (six animals per group), and LW (nine animals per group). Animals culled in LA had higher average daily weight gain than LW (P = 0.002), due to the reduced growth during winter typical for seasonal cervids in temperate zone, mediated by the photoperiod. Dressing percentage was significantly higher in LW and in the Lys+Met group (P = 0.002). Body condition score (P = 0.024), kidney fat index (KFI) (P = 0.005), and internal fat (P < 0.001) increased significantly with Lys+Met supplementation. During LW, KFI (P = 0.004) and kidney fat (P = 0.001) were also significantly higher than in LA. Blood creatinine concentration increased significantly for deer receiving Lys (P = 0.002) and Lys+Met (P < 0.001). Also, triglycerides level increased in Lys group (P < 0.001). These findings highlight the effects of Lys and Met supplementation on the growth and internal fat storage for winter survival, suggesting a different use of the supplemented resource according to the season. Also, the observed effects on protein and fat metabolism of fallow deer may influence the production of farmed animals, and offer interesting insights about the physiology of the species.

Keto analogues and amino acids (KAAA) supplementation can reduce blood ammonia concentrations in athletes undergoing high-intensity exercise under both ketogenic and thermoneutral conditions. This study evaluated the acute effects of KAAA supplementation on ammonia metabolism during extenuating endurance exercise in rats fed a ketogenic diet. In all, eighty male Fischer rats at 90 d of age were divided into eight groups, and some were trained using a swimming endurance protocol. A ketogenic diet supplemented with keto analogues was administered for 10 d. Administration of the ketogenic diet ended 3 d before the exhaustion test (extenuating endurance exercise). A ketogenic diet plus KAAA supplementation and extenuating endurance exercise (trained ketogenic diet supplemented with KAAA (TKKa)) increased blood ammonia concentrations by approximately 50 % compared with the control diet (trained control diet supplemented with KAAA (TCKa)) and similar training (effect size=1·33; statistical power=0·50). The KAAA supplementation reduced blood urea concentrations by 4 and 18 % in the control and ketogenic diet groups, respectively, compared with the groups fed the same diets without supplementation. The trained groups had 60 % lower blood urate concentrations after TCKa treatment than after TKKa treatment. Our results suggest that KAAA supplementation can reduce blood ammonia concentrations after extenuating endurance exercise in rats fed a balanced diet but not in rats fed a ketogenic diet.

Nutrition influences the microenvironment in the proximity of oocyte and affects early embryonic development. Elevated blood urea nitrogen, even in healthy dairy cows, is associated with reduced fertility and there is high correlation between blood urea levels and follicular fluid urea levels. Using a docking calculation (in silico), urea showed a favorable binding activity towards the ZP-N domain of ZP3, that of ZP2, and towards the predicted full-length sperm receptor ZP3. Supplementation of oocyte maturation medium with nutrition-related levels of urea (20 or 40 mg/dl as seen in healthy dairy cows fed on low or high dietary protein, respectively) dose-dependently increased: (i) the proportion of oocytes that remained uncleaved; and (ii) oocyte degeneration; and reduced cleavage, blastocyst and hatching rates. High levels of urea induced shrinkage in oocytes, visualised using scanning electron microscopy. Urea downregulated NANOG while dose-dependently upregulating OCT4, DNMT1, and BCL2 expression. Urea at 20 mg/dl induced BAX expression. Using mathematical modelling, the rate of oocyte degeneration was sensitive to urea levels; while cleavage, blastocyst and hatching rates exhibited negative sensitivity. The present data imply a novel role for urea in reducing oocyte competence and changing gene expression in the resultant embryos.

Kikuyugrass was analyzed for nitrate (expressed as KNO3) and soluble oxalate concentration after it was grown for 8 wk in nutrient solution supplemented with KCl, NaCl, or NH4NO3; fertilized in the greenhouse with urea and KNO3 at 112 kg N ha-1; and fertilized in the field in Hawaii and Panama with urea at 56 and 112 kg N ha-1. Both treated and untreated kikuyugrass grown in nutrient solution contained toxic levels of nitrates and soluble oxalates. Plants treated with urea in the greenhouse contained 0.4% nitrate (nontoxic) 72 h after treatment whereas those treated with KNO3 contained 2.36% nitrate (highly toxic). Fertilization of kikuyugrass with urea in Panama and Hawaii did not significantly affect soluble oxalate concentration, but nitrate concentration increased to potentially lethal levels (over 1.5% as KNO3, dry wt) in plants from Hawaii.

Urea and ammonium nitrate are components of 28% nitrogen liquid fertilizer (UAN) that is often used as an adjuvant in addition to surfactants or oils with herbicides. Ammonium nitrate and/or UAN fertilizer enhancement of nicosulfuron phytotoxicity to large crabgrass or yellow foxtail depended upon the associated oil or surfactant adjuvant. Ammonium nitrate reduced the effectiveness of most block copolymers but not other surfactants with nicosulfuron for large crabgrass. Urea never enhanced and often reduced surfactant and oil adjuvant enhancement of nicosulfuron. Ammonium nitrate or UAN, but not urea, enhanced nicosulfuron phytotoxicity to yellow foxtail when the spray carrier contained sodium bicarbonate. These research results indicated that enhancement of nicosulfuron efficacy from UAN is mainly from the ammonium nitrate component. However, the benefit to nicosulfuron from UAN or ammonium nitrate depended upon the associated surfactant or oil adjuvants.

Nicosulfuron efficacy varies with surfactant, natural salts in the spray water carrier, and added nitrogen fertilizer salts. Scanning electron micrographs (SEM) were taken of nicosulfuron spray droplet residue on large crabgrass in the greenhouse. Spray residue characteristics differ for nicosulfuron applied with surfactants alone and with specific salts. Uniform deposits with close contact to the leaf epicuticular surface generally related positively to nicosulfuron efficacy. Ammonium salt enhancement of nicosulfuron phytotoxicity when with surfactant X-77® related to a change from a ring to a uniform deposit. Spray mixtures containing Tween 20 or Atplus 300F surfactants that gave distinct dark amorphous deposits over anticlinal cell walls generally related to effective nicosulfuron treatments. Salts that were antagonistic to nicosulfuron phytotoxicity left a large amorphous deposit, including ammonium nitrate antagonism of nicosulfuron applied with Pluronic® P85 surfactant and general antagonism from sodium bicarbonate. The SEM information indicates that the effect of surfactants and salts on spray deposit characteristics influence nicosulfuron efficacy.

Seed dispersal is a crucial process in most plant invasions, but is notoriously difficult to study. One technique to identify the maternal source of dispersed seeds and newly established seedlings is labeling with a stable isotope. We tested whether foliar application of 15N-labeled urea would result in sufficient 15N enrichment to discriminate among seeds and seedlings grown from those seeds of the invasive shrub Lonicera maackii (Amur honeysuckle). We subjected mature L. maackii to all combinations of three concentrations of 15N-labeled urea (0.025 g L−1 [0.003 oz gal−1], 0.20 g L−1, and a 0 g L−1 control) and three temporal treatments (one application in August, one application in September, and five applications spaced every three weeks from June through August). Seeds were collected September to November; some of these were analyzed for %15N and others allowed to germinate and grow into seedlings under two treatments (in potting mix in greenhouse and in woodlot soil outdoors). Seedlings were harvested midway through the next growing season. We found that seeds from plants subjected to the three different concentrations had significantly different %15N levels, and there was a significant interaction between concentration and temporal treatment: the highest seed %15N levels were from plants sprayed five times with 15N-labeled urea, and the second highest from plants sprayed once in September. Similar patterns in %15N levels were found in seedlings, except that those from the 0.025 g L−1 spray treatment were only distinguishable from controls for seedlings grown outdoors in woodlot soil. These findings demonstrate that a single foliar application of 15N in early September is sufficient to label both seeds and seedlings of this invasive shrub, enabling one to identify the source of field-collected seeds or seedlings. This provides a tool for studying patterns and processes in seed dispersal of Amur honeysuckle and potentially other invasive plants.

Generally, <30% of dairy cattle’s nitrogen intake is retained in milk. Large amounts of nitrogen are excreted in manure, especially in urine, with damaging impacts on the environment. This study explores the effect of lowering dietary degradable nitrogen supplies – while maintaining metabolisable protein – on dairy cows’ performance, nitrogen use efficiency and gas emissions (NH3, N2O, CH4) at barn level with tied animals. Two dietary N concentrations (CP: 12% DM for LowN; 18% DM for HighN) were offered to two groups of three lactating dairy cows in a split-plot design over four periods of 2 weeks. Diets were formulated to provide similar metabolisable protein supply, with degradable N either in deficit or in excess (PDIN of 84 and 114 g/kg DM for LowN and HighN, respectively). Cows ingested 0.8 kg DM/day less on the LowN diet, which was also 2.5% less digestible. Milk yield and composition were not significantly affected. N exported in milk was 5% lower (LowN: 129 g N/day; HighN: 136 g N/day; P<0.001) but milk protein yield was not significantly affected (LowN: 801 g/day; HighN: 823 g/day; P=0.10). Cows logically ingested less nitrogen on the LowN diet (LowN: 415 g N/day; HighN: 626 g N/day; P<0.001) resulting in a higher N use efficiency (N milk/N intake; LowN: 0.31; HighN: 0.22; P<0.001). N excreted in urine was almost four times lower on the LowN diet (LowN: 65 g N/day; HighN: 243 g N/day; P<0.001) while urinary urea N concentration was eightfold lower (LowN: 4.6 g/l; HighN: 22.9 g/l; P<0.001). Ammonia emission (expressed in g/h in order to remove periods of the day with potential interferences with volatile molecules from feed) was also lower on the LowN diet (LowN: 1.03 g/h per cow; HighN: 1.25 g/h per cow; P<0.05). Greenhouse gas emissions (N2O and CH4) at barn level were not significantly affected by the amount of dietary N. Offering low amounts of degradable protein with suitable metabolisable protein amounts to cattle improved nitrogen use efficiency and lowered ammonia emissions at barn level. This strategy would, however, need to be validated for longer periods, other housing systems (free stall barns) and at farm level including all stages of manure management.

The aim of the present work was to assess the characteristics of the paracasein of two ewe's milk cheese varieties using various concentrations of urea and EDTA to solubilise caseins and calcium. The solubilised paracasein elements were evaluated by means of RP-HPLC and AAS. For this purpose cheeses with different physical and biochemical characteristics, i.e. Feta (53·1% moisture and pH 4·32) and Graviera Kritis (33·2% moisture and pH 5·54) were analysed. Soluble calcium of Feta was 71% of total calcium much higher than the 25% in Graviera. Treatment with 4 m urea fully solubilised Feta paracasein, whereas 6 m urea was needed to solubilise caseins from Graviera. Caseins were released from both cheeses by 100 mm EDTA. Solubilisation of paracasein induced by urea or EDTA was not significantly affected (P < 0·05) by the type of cheese. Similarly to urea, EDTA induced significantly (P < 0·05) lower solubilisation of αs1-casein in Graviera than in Feta, based on αs1-cn/β-cn ratio. A great part of calcium in both cheeses was solubilised by 50 mm EDTA while the release of casein was poor, confirming the important role of types of interactions other than protein-calcium bonds in the paracasein network. Hydrophobic interactions, hydrogen bonds and electrostatic attractions, contributed substantially to the paracasein stability of both cheese types. The interactions of αs1-casein with calcium played a more significant role in Graviera cheese than in Feta. Finally, the present study demonstrated that the profile of bonds and interactions within the cheese paracasein network was dynamicly configured by the conditions of cheese manufacture.

The aim of this study was to investigate 96 single-nucleotide polymorphisms (SNPs) from 54 candidate genes, and test the associations of the polymorphic SNPs with milk yield, composition, milk urea nitrogen (MUN) content and somatic cell score (SCS) in individual milk samples from Italian Brown Swiss cows. Milk and blood samples were collected from 1271 cows sampled once from 85 herds. Milk production, quality traits (i.e. protein, casein, fat and lactose percentages), MUN and SCS were measured for each milk sample. Genotyping was performed using a custom Illumina VeraCode GoldenGate approach. A Bayesian linear animal model that considered the effects of herd, days in milk, parity, SNP genotype and additive polygenic effect was used for the association analysis. Our results showed that 14 of the 51 polymorphic SNPs had relevant additive effects on at least one of the aforementioned traits. Polymorphisms in the glucocorticoid receptor DNA-binding factor 1 (GRLF1), prolactin receptor (PRLR) and chemokine ligand 2 (CCL2) were associated with milk yield; an SNP in the stearoyl-CoA desaturase (SCD-1) was related to fat content; SNPs in the caspase recruitment domain 15 protein (CARD15) and lipin 1 (LPIN1) affected the protein and casein contents; SNPs in growth hormone 1 (GH1), lactotransferrin (LTF) and SCD-1 were relevant for casein number; variants in beta casein (CSN2), GH1, GRLF1 and LTF affected lactose content; SNPs in beta-2 adrenergic receptor (ADRB2), serpin peptidase inhibitor (PI) and SCD-1 were associated with MUN; and SNPs in acetyl-CoA carboxylase alpha (ACACA) and signal transducer and activator of transcription 5A (STAT5A) were relevant in explaining the variation of SCS. Although further research is needed to validate these SNPs in other populations and breeds, the association between these markers and milk yield, composition, MUN and SCS could be exploited in gene-assisted selection programs for genetic improvement purposes.

Ingestion of small amounts of some types of condensed tannins (CTs) by ruminant livestock can provide nutritional, environmental and economic benefits. However, practical methods are needed to make these tannins more available to ruminant livestock. Results from previous trials with crude quebracho and black wattle tannin indicated that cattle and/or sheep would not preferentially drink water containing these tannins. Therefore, we conducted preference trials to determine if cattle and sheep would learn to prefer water containing purified grape seed tannin (GST) that provided up to 2% of their daily dry matter (DM) intake. After gradual exposure to increasing amounts of this tannin in water during a pre-trial period, five adult ewes and five yearling heifers fed lucerne (Medicago sativa) pellets (19% CP) were offered water and several concentrations of GST solutions for either 15 (sheep trial) or 20 days (cattle trial). We measured intake of all liquids daily. Concentrations of blood urea were also measured for heifers when they drank only tannin solutions or water. Both sheep and cattle developed preferences for water with GST in it over water alone (P < 0.01) although this preference appeared earlier in the trial for sheep than for cattle. For the sheep, mean daily intake of water alone and all tannin solutions (in total) was 0.6 and 6.1 l, respectively. For the cattle, mean daily intake of water and all tannin solutions in total was 21.8 and 20.6 l, respectively, in the first half of the trial and 10.8 and 26.1 l, respectively, in the second half of the trial. Compared with the other tannin solutions, both sheep and cattle drank more of the solution with the highest tannin concentration (2% of daily DM intake as GST) than of water on more trial days (P < 0.05). Ingestion of water with the highest concentration of GST reduced blood plasma urea concentration in the cattle by 9% to 14% (P ⩽ 0.10) compared with ingestion of water alone. Results from the trials suggest that providing grape seed and perhaps other CTs via drinking water may be a practical way to introduce CTs into sheep and cattle diets.

Glucose-6-phosphate dehydrogenase (G6PD), a regulatory enzyme of the pentose phosphate pathway from Brugia malayi, was cloned, expressed and biochemically characterized. The Km values for glucose-6-phosphate and nicotinamide adenine dinucleotide phosphate (NADP) were 0·25 and 0·014 mm respectively. The rBmG6PD exhibited an optimum pH of 8·5 and temperature, 40 °C. Adenosine 5′ [γ-thio] triphosphate (ATP-γ-S), adenosine 5′ [β,γ-imido] triphosphate (ATP-β,γ-NH), adenosine 5′ [β-thio] diphosphate (ADP-β-S), Na+, K+, Li+ and Cu++ ions were found to be strong inhibitors of rBmG6PD. The rBmG6PD, a tetramer with subunit molecular weight of 75 kDa contains 0·02 mol of SH group per mol of monomer. Blocking the SH group with SH-inhibitors, led to activation of rBmG6PD activity by N-ethylmaleimide. CD analysis indicated that rBmG6PD is composed of 37% α-helices and 26% β-sheets. The unfolding equilibrium of rBmG6PD with GdmCl/urea showed the triphasic unfolding pattern along with the highly stable intermediate obtained by GdmCl.

This work presents the preparation and characterization of N-doped TiO2 nanocrystals obtained by a solid-state reaction in vacuum with urea as the nitrogen source. The particle sizes of the products are smaller than 20 nm from the x-ray powder diffraction patterns and the transmission electron microscopy images. Different from the reported samples obtained in air or under dry N2 or NH3 gas flow, the doped nitrogen exists mainly as absorbed NOx groups but as smaller incorporated species in the nanocrystals, which is supported by the results from x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and ultraviolet–visible diffuse reflectance spectroscopy. Dependent on the nitrogen amount, the surface photovoltage (SPV) response reaches the maximum at the mediate molar ratio of 5:4 (urea to TiO2), which can be explained that proper nitrogen concentration can enhance the separation of the photogenerated carriers to improve the SPV intensity, but excess nitrogen can spread the impurity energy levels to narrow energy gaps, which reinforces the combination of the photogenerated electrons and holes and then decreases the SPV signal. The corresponding detailed discussion is also reported.

Amino-N is preserved because of the scarcity and nutritional importance of protein. Excretion requires its conversion to ammonia, later incorporated into urea. Under conditions of excess dietary energy, the body cannot easily dispose of the excess amino-N against the evolutively adapted schemes that prevent its wastage; thus ammonia and glutamine formation (and urea excretion) are decreased. High lipid (and energy) availability limits the utilisation of glucose, and high glucose spares the production of ammonium from amino acids, limiting the synthesis of glutamine and its utilisation by the intestine and kidney. The amino acid composition of the diet affects the production of ammonium depending on its composition and the individual amino acid catabolic pathways. Surplus amino acids enhance protein synthesis and growth, and the synthesis of non-protein-N-containing compounds. But these outlets are not enough; consequently, less-conventional mechanisms are activated, such as increased synthesis of NO∙ followed by higher nitrite (and nitrate) excretion and changes in the microbiota. There is also a significant production of N2 gas, through unknown mechanisms. Health consequences of amino-N surplus are difficult to fathom because of the sparse data available, but it can be speculated that the effects may be negative, largely because the fundamental N homeostasis is stretched out of normalcy, forcing the N removal through pathways unprepared for that task. The unreliable results of hyperproteic diets, and part of the dysregulation found in the metabolic syndrome may be an unwanted consequence of this N disposal conflict.

To access the fermentative response of equine caecal microbial population to nitrogen availability, an in vitro study was conducted using caecal contents provided with adequate energy sources and nitrogen as limiting nutrient. Two nitrogen (N) sources were provided, protein (casein) and non-protein (urea). Caecal fluid, taken from three cannulated horses receiving a hay–concentrate diet, was mixed with a N-free buffer–mineral solution. The influence of four N levels (3.7, 6.3, 12.5 or 25 mg of N in casein or urea) was studied using the gas production technique. Total volatile fatty acids (VFA), NH3-N and gas production were measured after a 24-h incubation period. Microbial biomass was estimated using adenine and guanine bases as internal markers, and ATP production was estimated stoichiometrically. Microbial growth efficiency (YATP) and gas efficiency (Egas) were estimated. Fermentation with casein as the sole N source was generally characterized by lower total VFA, NH3-N, total gas production and higher acetate : propionate (A : P) ratio and YATP than with urea. Results herein presented indicate that, under these in vitro conditions, caecal microbial population does in fact use urea N, but less efficiently than casein in terms of microbial growth.