Pierre-André Geraert

Metabolic and endocrine changes induced by chronic heat exposure in broiler chickens: biological and endocrinological variables.

The present study was designed to investigate the effect of chronic heat exposure (32 degrees constant) on plasma metabolites and hormone concentrations in broiler chickens. At 2 and 4 weeks of age, fifty-four male Shaver broiler chickens were allocated to one of three treatments: 22 degrees, ad lib. feeding (22AL), 32 degrees, ad lib. feeding (32AL) and 22 degrees, pair-feeding with the 32AL group (22PF). Ambient temperature was kept constant at either 22 or 32 degrees for 2 weeks. Plasma glucose, triacylglycerols, phospholipids, non-esterified fatty acids (NEFA), individual amino acids, uric acid, insulin, triiodothyronine (T3), thyroxine, corticosterone were determined. Sensitivity to exogenous insulin was also measured at 7 weeks of age. At 4 and 6 weeks of age, i.e. after 2 weeks at high ambient temperature, fasted 32AL chickens displayed similar concentrations of glucose and triacylglycerols to those of 22AL birds. When fed, 32AL chickens exhibited higher plasma levels of glucose and decreased concentrations of NEFA and amino acids. Feed restriction resulted in intermediate values. Concentrations of all plasma free amino acids were decreased under heat exposure except for aspartic acid, glutamic acid and phenylalanine. At 6 weeks of age, plasma T3 was reduced irrespective of the nutritional state, while plasma corticosterone concentrations were increased in 32AL birds compared with 22AL birds. Heat exposure did not change plasma insulin concentration in either fasted or fed chickens. The 32AL chickens displayed significantly reduced sensitivity to exogenous insulin when fasted, but an enhanced response to insulin when fed, compared with both 22 degrees groups. Such endocrinological changes could stimulate lipid accumulation through increased de novo lipogenesis, reduced lipolysis and enhanced amino acid catabolism under chronic heat exposure.

Effects of dietary supplementation of methionine and its hydroxy analog DL-2-hydroxy-4-methylthiobutanoic acid on growth performance, plasma hormone levels, and the redox status of broiler chickens exposed to high temperatures.

Heat stress is known to impair performance and to induce oxidative stress in poultry. The aim of the present study was to compare the effects of dietary supplementation of dl-methionine (dl-M) or the synthetic analog 2-hydroxy-4-methylthiobutanoic acid (dl-HMTBA) on broiler growth performance, plasma hormone levels, and some oxidative stress-related parameters under conditions of chronic exposure to high temperatures (HT). From 2 to 6 wk of age, male broiler chickens were reared under either a constant temperature of 32°C until 6 wk of age or a normal temperature scheme (gradual decrease to 18°C at 5 wk of age). Chicks in both the normal and HT treatments were provided with a commercial grower diet supplemented with either 1.0 or 1.2 g/kg of dl-M or 1.0 or 1.2 g/kg of dl-HMTBA. Because there were no effects of supplement dose, data were pooled over both doses within each temperature treatment. The chronic HT treatment impaired feed intake and BW gain, but these negative effects were less pronounced when the chickens received dl-HMTBA. Exposure to HT was also associated with decreased (P < 0.001) plasma thyroid hormones and increased (P < 0.0001) plasma corticosterone levels. At 4 wk of age, and irrespective of the supplemental source, chickens subjected to HT were characterized by significantly lower plasma TBA-reactive substance levels. In contrast, at 6 wk of age, plasma TBA-reactive substance levels were significantly increased by HT, but this effect was observed only for the chickens receiving dl-M and not for those receiving dl-HMTBA. High temperatures induced a significant increase in hepatic total glutathione (GSH) and oxidized GSH levels, regardless of the supplemental source. However, the hepatic ratios of reduced GSH to total GSH and reduced GSH to oxidized GSH were highest in chickens supplemented with dl-HMTBA. In conclusion, dl-HMTBA supplementation partially prevented the growth-depressing effects of chronic heat exposure compared with dl-M supplementation. It can be inferred that dl-HMTBA is more efficient in alleviating HT-induced oxidative damage because of a more favorable reduced GSH-to-total GSH ratio.

Are genetically lean broilers more resistant to hot climate

1. Genetically lean (LL) or fat (FL) male chickens were exposed to either high (32 degrees C) or control (22 degrees C) ambient temperature up to 9 weeks of age. They were fed on one of two isoenergetic diets differing in protein content: 190 or 230 g/kg. 2. At 22 degrees C, weight gain of LL broilers was the same as in FL chickens, but at the high temperature LL birds grew to a greater weight than FL ones. 3. Food conversion efficiency was not affected by ambient temperature in LL chickens but was depressed in FL ones at 32 degrees C. 4. Increasing dietary protein content did not alleviate heat-induced growth depression irrespective of the genotype. 5. Gross protein efficiency was higher in LL chickens and was less depressed at 32 degrees C than in FL birds. 6. Fat deposition decreased with increasing protein concentration at normal temperature in both genotypes; at high temperature, high protein content enhanced fatness, particularly in LL chickens. 7. Thus, genetically lean broilers demonstrated a greater resistance to hot conditions: this was indicated by enhanced weight gain and improved food and protein conversion efficiencies.

Comparative study of a new organic selenium source v. seleno-yeast and mineral selenium sources on muscle selenium enrichment and selenium digestibility in broiler chickens.

Two experiments were conducted on broiler chickens to compare the effect of a new organic Se source, 2-hydroxy-4-methylselenobutanoic acid (HMSeBA; SO), with two practical Se additives, sodium selenite (SS) and Se yeast (SY). The relative bioavailability of the different Se sources was compared on muscle (pectoralis major) total Se, selenomethionine (SeMet) and selenocysteine (SeCys) concentrations and apparent digestibility of total Se (ADSe). In the first experiment, from day (d) 0 to d21, Se sources were tested at different supplied levels and compared with an unsupplemented diet (NC). No significant effects were observed on growth performance during the experimental period. However, the different Se sources and levels improved muscle Se concentration compared with the NC, with a significant source effect in the following order: SS < SY < SO (P<0·05). Seleno-amino acids speciation results for NC, SY and SO at 0·3 mg Se/kg feed indicated that muscle Se was only present as SeMet or SeCys, showing a full conversion of Se by the bird. The second experiment (d0-d24) compared SS, SY or SO at 0·3 mg Se/kg feed. The ADSe measurements carried out between d20 and d23 were 24, 46 and 49% for SS, SY and SO, respectively, with significant differences between the organic and mineral Se sources (P<0·05). These results confirmed the higher bioavailability of organic Se sources compared with the mineral source and demonstrated a significantly better efficiency of HMSeBA compared with SY for muscle Se enrichment.

Effects of dietary protein content and 2-hydroxy-4-methylthiobutanoic acid or DL-methionine supplementation on performance and oxidative status of broiler chickens.

Besides its typical role as an amino acid in protein synthesis, methionine is an important intermediate in methylation reactions. In addition, it can also be converted to cysteine and hence plays a role in the defence against oxidative stress. The present study was conducted to investigate further the role of DL-methionine (DLM) and its hydroxy analogue, DL-2-hydroxy-4-methylthiobutanoic acid (DL-HMTBA), on zootechnical performance and oxidative status of broiler chickens. Male broiler chickens were reared on two diets differing in crude protein (CP) content (low-protein, 18·3 % v. high-protein, 23·2 % CP) and were supplemented either with 0·25 % DLM or 0·25 % DL-HMTBA. Reducing the dietary protein content resulted in an impaired body weight gain (P < 0·0001). However, supplementation of DL-HMTBA to the low-protein diet partially alleviated these negative effects (P = 0·0003). This latter phenomenon could be explained by the fact that chickens fed DL-HMTBA-supplemented diets displayed a better antioxidant status as reflected in lower lipid peroxidation probably as a consequence of their higher hepatic concentrations of total and reduced glutathione compared with their DLM counterparts. On the other hand, within the high protein levels, uric acid might be an important antioxidant to explain the lower lipid peroxidation of high-protein DL-HMTBA-supplemented chickens. Hepatic methionine sulfoxide reductase-A gene expression was not significantly affected by the dietary treatments. In conclusion, the present study indicates that there are interactions between dietary protein content and supplementation of methionine analogues with respect to broiler performance and antioxidant status, also suggesting a causal link between these traits.

Energy balance of laying hens selected on residual food consumption

1. Energy balance of adult hens divergently selected for high (R + ) or low (R- ) residual food consumption was investigated using indirect calorimetry. Three experiments were conducted: feeding behaviour of individual hens, hens having free access to food or fasting and hens tube-fed at 70, 100 or 130% of the control intake of both lines. 2. R + hens ate significantly more than R- (+ 48%). This difference was maximum at the onset of the light (+ 120%) and not significant during the rest of the light period. Although both lines spent the same total time eating, R + hens exhibited more frequent but shorter meals than R- ones, suggesting a higher feeding activity in R + hens. 3. True metabolisable energy (TME) intake was 28% greater in R+ than in R- birds. Basal heat production did not differ significantly between genotypes. Heat increment of feeding (HI) or diet-induced thermogenesis was significantly enhanced in R + birds: + 23.9 vs 13.7 kJ/100 kJ TME intake in R- . 4. When tube-fed and placed in darkness...

Effect of 2-hydroxy-4-methylselenobutanoic acid as a dietary selenium supplement to improve the selenium concentration of table eggs1

The aim of this study was to compare the effects of a new organic Se [2-hydroxy-4-methylselenobutanoic acid (HMSeBA)] with routinely used mineral and organic Se sources (sodium selenite and selenized yeast) on chosen performance criteria and Se deposition in egg and muscle of laying hens. A total of 240 laying hens (40 wk of age) were randomly assigned to 6 treatments for 56 d with 8 replicates of 5 hens per replicate. The 6 treatments were as follows: control group received basal diet without Se supplementation; the second, fourth, and sixth experimental groups (SS-0.2, SY-0.2, and HMSeBA-0.2, respectively) were fed basal diet supplemented with Se at 0.2 mg/kg from sodium selenite, selenized yeast, and HMSeBA, respectively; and the third and fifth experimental groups (SY-0.1, and HMSeBA-0.1, respectively) were fed basal diet supplemented with Se at 0.1 mg/kg from selenized yeast and HMSeBA, respectively. No difference was observed among dietary treatments on feed intake, egg weight, and laying rate. All hens fed the Se-supplemented diets exhibited greater total Se contents in their eggs compared with control hens (P < 0.01). The egg Se concentrations were greater in hens fed organic Se (HMSeBA-0.2, P < 0.01, and SY-0.2, P < 0.01) than those fed the SS-0.2. In addition, hens fed the diet with HMSeBA-0.2 accumulated more Se in their eggs (+28.78%; P < 0.01) and muscles (+28%; P < 0.01) than those fed the diet supplemented with SY-0.2. These results showed the greater ability of HMSeBA to increase Se deposition in eggs and breast muscle of laying hens, which can subsequently lead to greater supply of Se for humans.

Effect of pH on l- and d-methionine uptake across the apical membrane of Caco-2 cells

The transport systems involved in intestinal methionine (Met) absorption are described as Na(+)-dependent and Na(+)-independent mechanisms. However, since recent studies have suggested the importance of the H(+) gradient as a driving force for intestinal nutrient absorption, the aim of the present work was to test whether Met transport across the apical membrane of Caco-2 cells is affected by extracellular pH. The results show that l- and d-Met uptake was increased by lowering extracellular pH from 7.4 to 5.5, in both the presence and absence of Na(+). Cis-inhibition experiments revealed that inhibition of l-Met transport by 2-aminobicyclo[2,2,1]heptane-2-carboxylic acid (BCH) or l-lysine (l-Lys) was higher at a pH of 5.5. Moreover, the BCH-insensitive component was not affected by pH, whereas the l-Lys-insensitive component was increased by lowering extracellular pH, thus suggesting the participation of system L. The contribution of another mechanism, sensitive to both BCH and l-Lys, was also considered. The inhibition obtained with taurine (Tau) was also higher at a pH of 5.5, thus suggesting the involvement of system B(0,+) on pH-stimulated component. As for d-Met uptake, the results showed higher inhibition with l-Lys and Tau at a pH of 5.5 and no effect on the l-Lys- or Tau-insensitive component. In conclusion, Met transport across the apical membrane of Caco-2 cells is increased by low extracellular pH as the result of the stimulation of two transport systems functionally identified with systems L and B(0,+) for l-Met and with system B(0,+) for d-Met.

2-Hydroxy-4-methylselenobutanoic acid induces additional tissue selenium enrichment in broiler chickens compared with other selenium sources

Two experiments were conducted in broiler chickens to compare the effect of different Se sources on Se tissue enrichment: sodium selenite (SS), seleno-yeast (SY), and a new organic Se source (SO) containing 2-hydroxy-4-methylselenobutanoic acid (HMSeBA) as an active substance. For each experiment, treatments differed only in source or dose of Se additive. Relative efficiency was compared by plasma and tissue [muscle (pectoralis major) and liver] total Se concentrations. The first experiment compared Se sources (SS, SY, and SO) at different concentrations (mg of Se/kg of feed; SS-0.3; SY-0.1 and -0.3; SO-0.1 and -0.3; and a negative control, 0) in broilers between 0 and 42 d of age. Plasma, liver, and muscle Se concentrations were improved by all Se sources at both d 21 and 42 compared with the negative control group. Between Se sources, minor differences were observed for plasma and liver results, whereas a significant dose effect was observed from 0.1 to 0.3 mg of Se/kg of feed (P < 0.05) for each source. Muscle Se concentrations were improved such as SO > SY > SS (P < 0.05). Moreover, the relative muscle Se enrichment comparison, using linear regression slope ratio, indicated an average of 1.48-fold (95% CI 1.38, 1.58) higher Se deposition in muscle for SO compared with SY. In the second experiment, excessive dietary doses of 5 mg of Se/kg of feed from SS and SO showed a lower deleterious effect of SO on BW and feed intake in comparison with standard Se doses (P < 0.05). Seleno amino acid measurements conducted on different tissues of animals fed SO at 0.5 mg/kg of feed showed that HMSeBA is fully converted into selenomethionine and selenocysteine. These results of both experiments demonstrate the higher relative bioavailability of SO compared with SS and SY as determined through tissue Se enrichment.

The methionine precursor DL-2-hydroxy-(4-methylthio)butanoic acid protects intestinal epithelial barrier function.

DL-2-hydroxy-(4-methylthio)butanoic acid (HMTBA) is a source of dietary methionine (Met) that is widely used in poultry nutrition. We have previously shown that HMTBA is preferentially diverted to the transsulfuration pathway, which gives antioxidant metabolites such as taurine and glutathione. Therefore, here we hypothesize that this Met source can protect epithelial barrier function in an in vitro model of intestinal inflammation of Caco-2 cells. The results show that HMTBA prevents the increase in paracellular permeability induced by H2O2 or tumour necrosis factor-α. This effect can be attributed to the increased production of taurine and reduced glutathione. Similar results were obtained for DL-Met, although the protective role of the amino acid was less pronounced than that of the hydroxy analogue. In conclusion, the diversion to the transsulfuration pathway means that this Met precursor is of greater value than previously thought, due to its capacity to improve intestinal homeostasis and the quality of poultry products destined for human consumption.