Ascites in broilers. 2. Disturbances in the hormonal regulation of metabolic rate and fat metabolism

L-Citrulline Influences the Body Temperature, Heat Shock Response and Nitric Oxide Regeneration of Broilers Under Thermoneutral and Heat Stress Condition

Heat stress (HS) adversely affects several physiological responses in organisms, but the underlying molecular mechanisms involved are yet to be fully understood. L-Citrulline (L-Cit) is a nutraceutical amino acid that is gaining research interest for its role in body temperature regulation and nitric oxide synthesis. This study investigated whether dietary supplementation with L-Cit (1% of basal diet) could ameliorate the effects of acute HS on thermotolerance, redox balance, and inflammatory responses of broilers. Ross 308 broilers (288 chicks) were subjected to two environments; thermoneutral at 24°C (TNZ) or HS at 35°C for 5 h, and fed two diets; control or L-Cit. The results showed that HS increased the ear, rectal (RT), and core body (CBT) temperatures of broilers, along with higher respiratory rate. The RT and CBT readings were intermittently affected with time effect, whereas, L-Cit supplementation lowered the mean CBT than the control diet. Antioxidant assays showed that superoxide dismutase was increased during HS, while, catalase was promoted by L-Cit supplementation. In addition, L-Cit induced glutathione peroxidase activity compared to the control diet during HS. Hypothalamic heat shock protein (HSP)-90 was upregulated by HS, but L-Cit downregulated heat shock factor (HSF)-1, and HSP 60 mRNA expressions. HSF 3 mRNA expression was downregulated by L-Cit under TNZ condition. More so, HS increased the plasma nitric oxide (NO) concentration but lowered the total NO synthase (tNOS) activity. In contrast, L-Cit supplementation limited NO production but increased the tNOS activity. Arginase activity was increased in the control fed group during HS but L-Cit supplementation lowered this effect. The NOS-COX pathway was significantly affected under TNZ condition, since L-Cit supplementation downregulated the mRNA expression of iNOS-COX2 in the hypothalamus, and further reduced the serum PGE2 concentration. Together, these data indicates that L-Cit influenced the antioxidant defense, heat shock response and nitric oxide regeneration both under thermoneutral and HS conditions; and that L-Cit may be directly and/or indirectly involved in the central regulation of body temperature.

Regulation of myostatin expression is associated with growth and muscle development in commercial broiler and DMC muscle

Myostatin is a negative regulator of skeletal muscle growth. Muscle tissue is the largest tissue in the body and influences body growth. Commercial Avian broiler chickens are selected for high growth rate and muscularity. Daweishan mini chickens are a slow growing small-sized chicken breed. We investigated the relations between muscle (breast and leg) myostatin mRNA expression and body and muscle growth. Twenty chickens per breed were slaughtered at 0, 30, 60, 90, 120, and 150 days of age. Body and muscle weights were higher at all times in Avian chickens. Breast muscle myostatin expression was higher in Avian chickens than in Daweishan mini chickens at day 30. Myostatin expression peaked at day 60 in Daweishan mini chickens and expression remained higher in breast muscle. Daweishan mini chickens myostatin expression correlated positively with carcass weight, breast and leg muscle weight from day 0 to 60, and correlated negatively with body weight from day 90 to 150, while myostatin expression in Avian chickens was negatively correlated with carcass and muscle weight from day 90 to 150. The results suggest that myostatin expression is related to regulation of body growth and muscle development, with two different regulatory mechanisms that switch between days 30 and 60.

Biological mechanisms discriminating growth rate and adult body weight phenotypes in two Chinese indigenous chicken breeds

Background

Intensive selection has resulted in increased growth rates and muscularity in broiler chickens, in addition to adverse effects, including delayed organ development, sudden death syndrome, and altered metabolic rates. The biological mechanisms underlying selection responses remain largely unknown. Non-artificially-selected indigenous Chinese chicken breeds display a wide variety of phenotypes, including differential growth rate, body weight, and muscularity. The Wuding chicken breed is a fast growing large chicken breed, and the Daweishan mini chicken breed is a slow growing small chicken breed. Together they form an ideal model system to study the biological mechanisms underlying broiler chicken selection responses in a natural system. The objective of this study was to study the biological mechanisms underlying differential phenotypes between the two breeds in muscle and liver tissues, and relate these to the growth rate and body development phenotypes of the two breeds.

Results

The muscle tissue in the Wuding breed showed higher expression of muscle development genes than muscle tissue in the Daweishan chicken breed. This expression was accompanied by higher expression of acute inflammatory response genes in Wuding chicken than in Daweishan chicken. The muscle tissue of the Daweishan mini chicken breed showed higher expression of genes involved in several metabolic mechanisms including endoplasmic reticulum, protein and lipid metabolism, energy metabolism, as well as specific immune traits than in the Wuding chicken. The liver tissue showed fewer differences between the two breeds. Genes displaying higher expression in the Wuding breed than in the Daweishan breed were not associated with a specific gene network or biological mechanism. Genes highly expressed in the Daweishan mini chicken breed compared to the Wuding breed were enriched for protein metabolism, ABC receptors, signal transduction, and IL6-related mechanisms.

Conclusions

We conclude that faster growth rates and larger body size are related to increased expression of genes involved in muscle development and immune response in muscle, while slower growth rates and smaller body size are related to increased general cellular metabolism. The liver of the Daweishan breed displayed increased expression of metabolic genes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3845-9) contains supplementary material, which is available to authorized users.

Ascites in poultry: Recent investigations

In recent years, ascites research has centred on gaining an increased understanding of pulmonary hypertension syndrome together with the potential role of primary cardiac pathologies. The impact at a cellular level of factors which trigger ascites and substances that protect against it has also been documented. Primary pulmonary hypertension has been induced when birds are exposed to hypoxia during incubation. The conditions experienced during this phase of development may impact on the ability of the bird to regulate its basal metabolic rate through endocrine signals controlled by thyroid activity. The extent of ventilation in the lung influences the ability of the bird to oxygenate haemoglobin. Ventilation/ perfusion mismatches may occur prior to or post-hatching. This factor has been studied extensively using the pulmonary artery/bronchus clamp model. At high altitude, a decreased ventilation/perfusion ratio may occur following the effective increase in physiological dead space due to the lowered oxygen tension at the level of the parabronchi. This explains the mechanism by which ascites is triggered by hypoxia in this particular situation. The effects of ascites are ameliorated by the use of beta agonists and dietary arginine, which act by increasing ventilation and blood flow in the lungs and thus correcting a ventilation/perfusion mismatch. Transient bacterial and viral infections may also influence the induction of pulmonary hypertension. The increases in blood viscosity associated with ascites are most probably a consequence of the condition rather than a cause. A bird may alleviate the effects of pulmonary hypertension by decreasing blood viscosity through inhibition of platelet function, increased erythrocyte deformability and the production of coronary relaxants. Evidence is accumulating that primary cardiac pathology may be associated with a number of ascites cases. Broilers that subsequently develop ascites, exhibit lower heart rates than their normal flock mates. Furthermore, during ascites, hypoxic broilers exhibit bradycardia as opposed to the expected tachycardia. In these cases, a tachycardia induced by feed restriction may protect the bird by raising its cardiac output. Right atrio-ventricular regurgitant flow velocities in chickens are relatively slow compared with similar regurgitant flows induced by pulmonary hypertension in other species. The conduction system in the avian heart is specialized and contains a recurrent bundle branch that innervates the right atrio-ventricular valve, thus initiating active valve closure before right ventricular systole. This predisposes the heart to right ventricular volume overload through a valvular incompetance following a failure of valvular innervation. The resultant elevated diastolic wall stress can trigger the production of angiotensin II and its converting enzyme, which mediate ventricular hypertrophy. Subclinical myocardial damage, irrespective of its cause, can be detected by the presence of troponin T in the blood. Reactive oxygen species may damage cell membranes compromising cellular function in a number of body systems. A positive correlation exists between oxidized glutathione concentrations and right ventricular weight ratio. This indicates a failure to cope with oxidative stress at the level of the respiratory membrane. It is not known if it is possible to modulate levels of antioxidants at this location and hence protect the bird. The final description of the ascites aetiology may lie in the concept of a circuit of events between the cardiac, pulmonary and vascular systems that satisfy the metabolic requirements of the bird. A deficit in one of these systems, at a level that prevents adequate compensation from other components, triggers the pathological cascade that results in the end point of clinical ascites.

Partial pressure of carbon dioxide in the venous blood of young birds as a predictor of ascites susceptibility in broiler chickens

In order to investigate the relationship between carbon dioxide tensions in the venous blood of young chickens and ascites susceptibility, one hundred day-old chickens from two pure broiler breeder lines differing in susceptibility to ascites syndrome were obtained and reared at low environmental temperature. Weekly, blood samples were taken for the determination of blood gas parameters and plasma thyroid hormone levels. Dead birds were examined for lesions of ascites daily and all survived birds were autopsied at the end of the trials. In cold conditioning, the cumulative incidence of right ventricular hypertrophy (RVH) and ascites was 78% (39/50) in fast-growing (line A) and 50% (25/50) in slow-growing (line B) chickens, confirming that line A chickens had higher susceptibility to ascites than line B chickens. At 12 days of age, the mean pCO(2) tension was significantly (P < 0.01) higher in the venous blood of line A than line B chickens. During the experiment, the majority of line A and line B chickens showing RVH and ascites exhibited pCO(2) tensions equal to, or exceeding 50 mmHg at 12 days of age. Additionally, fast-growing chickens showed significantly lower plasma T3 and T4 concentrations than slow-growing chickens. In conclusion, our data indicate that carbon dioxide pressure in the venous blood of early postnatal broiler chickens could be used as a valuable predictor in the selection of birds susceptible to pulmonary hypertension and ascites. The function of thyroid hormones should also be taken into consideration in further selection procedures for meat-type chickens.

Comparative study of myocardial high energy phosphate substrate content in slow and fast growing chicken and in chickens with heart failure and ascites

In order to explain the biochemical mechanisms associated with deteriorating heart function in broiler chickens, this study compared myocardial high energy phosphate substrates in leghorns, feed restricted (Broilers-Res) broilers, ad libitum fed broilers (Broilers-AL), and in broilers that developed heart failure and ascites. The profile of adenine nucleotide content in the heart tissue did not differ between leghorns and Broilers-Res, but there were significant differences among Broilers-Res, Broilers-AL, and broilers with ascites. During intensive growth periods, leghorns and Broilers-Res showed increasing trends in heart ATP levels, whereas in fast growing broilers the heart ATP declined (p<0.021). ATP:ADP and ATP:CrP ratios increased with age in both leghorn and Broilers-Res, declined in fast growing broilers, and were the lowest in broilers that developed heart failure. The changes in heart high energy phosphate profile in broilers suggest that the energy demand of the heart during a rapid growth phase may exceed the bird's metabolic capacity to supply adequate levels of high energy phosphate substrate. The insufficiency of energy substrate likely contributes to the declining heart rate. In some individuals this may lead to impaired heart pump function, and in more severe cases may progress to heart pump failure.

Increased calcium deposits and decreased Ca2+-ATPase in right ventricular myocardium of ascitic broiler chickens

Right ventricular hypertrophy and failure is an important step in the development of ascites syndrome (AS) in broiler chickens. Cytoplasmic calcium concentration is a major regulator of cardiac contractile function and various physiological processes in cardiac muscle cells. The purpose of this study was to measure the right ventricular pressure and investigate the precise ultrastructural location of Ca(2+) and Ca(2+)-ATPase in the right ventricular myocardium of chickens with AS induced by low ambient temperature. The results showed that the right ventricular diastolic pressure of ascitic broilers was significantly higher than that of control broilers (P < 0.01), and the maximum change ratio of right intraventricular pressure (RV +/- dp/dt(max)) of ascitic broilers was significantly lower than that of the controls (P < 0.01). Extensively increased calcium deposits were observed in the right ventricular myocardium of ascitic broilers, whereas in the age-matched control broilers, calcium deposits were much less. The Ca(2+)-ATPase reactive products were obviously found on the sarcoplasmic reticulum and mitochondrial membrane of the control right ventricular myocardium, but rarely observed in the ascitic broilers. The data suggest that in ascitic broilers there is the right ventricular diastolic dysfunction, in which the overload of intracellular calcium and the decreased Ca(2+)-ATPase activity might be the important factors.

Pathophysiology of heart failure in broiler chickens: structural, biochemical, and molecular characteristics

Modern strains of fast-growing meat type poultry are highly susceptible to heart failure. Heart-related mortalities are observed predominantly in fast-growing broiler chickens, with ascites and sudden death syndrome being the most common heart-related conditions in modern broiler flocks. This paper examines the role of structural, molecular, and biochemical factors pertinent to the pathophysiology of heart failure in fast-growing broilers. Evidence explaining the pathogenesis of acute and chronic heart failure, in the context of the underlying molecular and biochemical changes in the cardiomyocytes, contractile apparatus, and extracellular matrix in the ventricular myocardium are critically evaluated and discussed with reference to the clinical signs associated with deterioration of heart pump function. The secondary pathophysiological effects on the cardiovascular system, resulting from hemodynamic changes associated with the failing heart pump, are also reviewed and critically discussed.

Genetic mapping of quantitative trait loci affecting susceptibility in chicken to develop pulmonary hypertension syndrome

Pulmonary hypertension syndrome (PHS), also referred to as ascites syndrome, is a growth-related disorder of chickens frequently observed in fast-growing broilers with insufficient pulmonary vascular capacity at low temperature and/or at high altitude. A cross between two genetically different broiler dam lines that originated from the White Plymouth Rock breed was used to produce a three-generation population. This population was used for the detection and localization of quantitative trait loci (QTL) affecting PHS-related traits. Ten full-sib families consisting of 456 G2 birds were typed with 420 microsatellite markers covering 24 autosomal chromosomes. Phenotypic observations were collected on 4202 G3 birds and a full-sib across family regression interval mapping approach was used to identify QTL. There was statistical evidence for QTL on chicken chromosome 2 (GGA2), GGA4 and GGA6. Suggestive QTL were found on chromosomes 5, 8, 10, 27 and 28. The most significant QTL were located on GGA2 for right and total ventricular weight as percentage of body weight (%RV and %TV respectively). A related trait, the ratio of right ventricular weight as percentage to total ventricular weight (RATIO), reached the suggestive threshold on this chromosome. All three QTL effects identified on GGA2 had their maximum test statistic in the region flanked by markers MCW0185 and MCW0245 (335-421 cM).

Anatomical parameters of cardiopulmonary system in three different lines of chickens: further evidence for involvement in ascites syndrome

The present study was designed to compare the anatomical parameters of the cardiopulmonary system in three different lines of chickens with different susceptibility to ascites syndrome. Eggs from three different genetic lines-commercial broiler and layer lines and one native to Iran--were incubated and hatched, and 1-day-old chicks used. The relative heart and lung weights, the volumes of the heart, lung and thorax cavity, the incidence of ascites, and the related physiological parameters in these chickens were followed. Lung weight as a percentage of body weight, the relative lung and heart volume, and the volumes of the thorax cavity, before and after removing heart and lung tissues, were lower in fast-growing broiler chickens compared with the layer and native chickens. Additionally, most of these parameters (e.g. relative lung weight, lung volume and thorax cavity) were significantly decreased with age in broiler chickens but were increased in layer and native chickens, which was concomitant with the incidence of ascites in broiler chickens. Our data indicate that all cardiopulmonary parameters investigated are extremely unfavourable to broiler chickens and suggest a reduction in gas exchange area in broilers, and therefore higher susceptibility to pulmonary hypertension and ascites.

Production and growth related disorders and other metabolic diseases of poultry – A review

In humans, metabolic complaints may be associated with a failure in one of the body hormone or enzyme systems, a storage disease related to lack of metabolism of secretory products because of the lack of production of a specific enzyme, or the breakdown or reduced activity of some metabolic function. Some of these disorders also occur in poultry, as do other important conditions such as those associated with increased metabolism, rapid growth or high egg production that result in the failure of a body system because of the increased work-load on an organ or system. These make up the largest group of poultry diseases classified as metabolic disorders and cause more economic loss than infectious agents. Poultry metabolic diseases occur primarily in two body systems: (1) cardiovascular ailments, which in broiler chickens and turkeys are responsible for a major portion of the flock mortality; (2) musculoskeletal disorders, which account for less mortality, but in broilers and turkeys slow down growth (thereby reducing profit), and cause lameness, which remains a major welfare concern. In addition, conditions such as osteoporosis and hypocalcaemia in table-egg chickens reduce egg production and can kill.

Effect of chronic hypoxia during embryonic development on physiological functioning and on hatching and post-hatching parameters related to ascites syndrome in broiler chickens

The present study was designed to investigate the effect of different atmospheric pressure on the endogenous functions of broiler chickens during embryonic, hatching and growing periods related to ascites. Eggs from a commercial broiler line were incubated in two similar commercial incubators at high and low altitudes. The effect on embryonic development and physiological functions including hatching parameters, incidence of ascites and growth performance were examined. Embryos incubated at high altitude had higher plasma tri-iodothyronine, thyroxine, corticosteroid and lactic acid levels, and hatched earlier than those incubated at low altitude. Embryonic mortality was higher at high altitude. Chickens that had been incubated at high altitude showed less right ventricular hypertrophy and ascites mortality than those incubated at low altitude. It was concluded that different atmospheric pressure during incubation interacts with the endocrine functions of the embryo and hence affects hatching parameters, thereby influencing ascites susceptibility.

Hyper- or hypothyroidism: its association with the development of ascites syndrome in fast-growing chickens

The ascites syndrome in broiler chickens is attributed to the progress in genetic selection for rapid growth, coupled with the metabolic burden imposed by exposure to a relatively low-ambient temperature (T(a)). The syndrome is mainly characterized by hematocrit elevation, decline in blood oxygen saturation, accumulation of fluid in the abdominal cavity, and finally, death. Ascitic chickens have demonstrated hypothyroidism coupled with a marked stress response (high corticosterone concentration) and reduction in the hemoglobin content. The objective of the present study was to examine the role of thyroid and corticosterone hormones in the development of the syndrome. Ascites was induced by exposure to a gradually declining T(a) and supplementation of a pellet-form diet. Exogenous thyroxin (T(4)) and propylthiouracil (PTU) (in Experiments 1 and 2, respectively) were supplemented in drinking water to induce hyper- or hypothyroidism, respectively. Ascites syndrome was developed in 21.5% and 23% of the birds exposed to ascites-induced conditions (Exps. 1 and 2, respectively). Excess T(4) (Exp. 1) significantly reduced the percentage of ascites (down to 7%), whereas PTU (Exp. 2) significantly increased the appearance of the syndrome (35%). In the T(4)-treated chickens, although the T(4) concentration reached pharmacological levels, the triiodothyronine (T(3)) concentration remained within physiological levels, whereas T(3) in the ascitic birds exhibited a reduction pattern similar to that observed in the ascitic non-supplemented ones. In the PTU-treated chickens, however, both ascitic and non-ascitic birds demonstrated significant reductions in both T(4) and T(3) concentrations. In both experiments, ascitic chickens exhibited a considerable stress response, characterized by a significant and persisted elevation in plasma corticosterone concentration, which was in accordance with a similar elevation of hematocrit, and the PTU-treated non-ascitic birds exhibited a similar stress response. At 5 weeks of age, ascitic birds and the PTU-treated non-ascitic ones exhibited significant reductions in the hemoglobin content of their red blood cells. It may be concluded that deficiency in the thyroid hormones and elevated corticosterone may play a key deleterious role in the development of the ascites syndrome.

The effects of toasting canola meal on body weight, feed conversion efficiency, and mortality in broiler chickens

It is hypothesized that the moisture incorporated into canola meal (CM) during desolventization, as sparge steam, promotes toasting. Elimination of toasting of CM would result in higher digestible amino acid content, but it is not known if it is required to reduce anti-nutritional factors. Therefore, the objectives of this study were to determine if suspending the use of sparge steam would prevent toasting and to study the effects of toasting on broiler chicken performance. Conventional toasted CM (TCM) and a hexane laden, nontoasted CM (NTCM) were collected from a commercial crushing plant. NTCM was desolventized in a research desolventizer/toaster without the use of sparge steam, producing a yellow-colored meal. The meals were fed to broiler chickens from 0 to 39 d and replaced 0, 20, 40, 60, 80, and 100% of the soybean meal (SBM) in wheat-based diets. Elimination of toasting increased broiler weight from 0.606 and 2.148 to 0.618 and 2.181 kg at 19 and 39 d of age, respectively. The feed ratio (0 to 19 d) increased from 0.637 to 0.642, but toasting did not affect mortality. Total mortality and chronic heart failure between 19 and 39 d increased with level of CM addition from 5.2 to 13.9% and 1.9 to 9.6%, respectively. Chronic heart failure in males, but not females, was increased from 3.3 to 17.4% with increasing CM level. In conclusion, desolventization without sparge steam produced a nontoasted meal and improved broiler growth and feed efficiency in comparison to TCM. Therefore, NTCM could be fed to broiler chickens.

The effects of dietary L-carnitine supplementation on the performance, organ weights and circulating hormone and metabolite concentrations of broiler chickens reared under a normal or low temperature schedule

1. The present study examined the effects of the addition of 100 mg/kg L-carnitine to the basal starter (containing 17.8 mg/kg L-carnitine) and finisher (containing 22.9 mg/kg L-carnitine) diets on performance, organ weights and plasma hormone and metabolite concentrations of male and female broiler chickens. The broiler chickens were reared either in a room with a normal temperature (NT) program or with a low temperature (LT) program (rapid decrease from 28 degrees C to 20 degrees C at 14 d of age). 2. Broiler chickens reared under the LT schedule consumed more food and attained a greater body weight at 42 d of age than their counterparts reared under NT schedule, without any difference in food efficiency or abdominal fat content. Dietary L-carnitine supplementation had no significant effects on any of these production parameters, except for a reduction in the abdominal fat content of female NT chickens. However, the LT schedule and dietary L-carnitine supplementation greatly increased absolute and proportional heart weights. The elevated heart weights were not due to right ventricle hypertrophy. 3. Both the LT program and L-carnitine supplementation increased circulating plasma triiodothyronine concentrations. There were also some transient effects of both experimental variables on plasma growth hormone, glucose and triglyceride concentrations. 4. L-carnitine did not improve broiler performance. However, this result does not mean that L-carnitine supplementation cannot have beneficial effects in other circumstances. In view of the elevated proportional heart weights, it can also be argued that L-carnitine is a potential agent for reducing the incidence of metabolic diseases in broiler chickens.

Metabolic disturbances in male broilers of different strains. 2. Relationship between the thyroid and somatotropic axes with growth rate and mortality

Seven male broiler strains (Arbor Acres, Avian Farms, Cobb-500, Hubbard-Peterson, ISA, Naked Neck, and Ross) were compared for their growth rate, feed efficiency, and mortality due to sudden death and ascites. In addition, weekly plasma levels of thyroid hormones [3,3',5-triiodothyronine (T3) thyroxine (T4), T3: T4 ratio, growth hormone (GH), and insulin-like growth factor-I (IGF-I)] were determined. The highly productive, commercial strains were very similar in their endocrine profiles but differed markedly from the Naked Neck chickens. Naked Neck chickens were characterized by higher plasma T3 and lower T4 levels at similar ages as well as when compared on the same body weight basis. The present findings support the hypothesis that the slightly hypothyroid state of high productive broilers renders them more sensitive to metabolic disorders. Naked Neck chickens also had higher plasma GH levels than those of their age-matched commercial broilers. The coefficient of variation for GH was highest for Naked Neck chickens, which is indicative for an amplified GH burst amplitude. It may be stated that changes in plasma thyroid hormone concentration in indirect response to selection for low feed conversion and fast growth may be causatively linked to susceptibility for metabolic disturbances such as sudden death syndrome and ascites.

Performance and physiological variables in broiler chicken lines differing in susceptibility to the ascites syndrome: 1. Changes in blood gases as a function of ambient temperature

1. Male broilers of 5 genetic stocks (A, B, C, D, E) selected in different ways for fast growth and low food conversion ratio (FCR) and differing in ascites sensitivity were subjected to 2 different ambient temperature step down regimens: high temperature (HT: 33 to 20 degrees C over 33 d) and low temperature (LT: 30 to 15 degrees C over 17 d). 2. Ascites incidence was recorded daily. Food intake and body weight gain were measured weekly and FCR was calculated. Heat production (Hp) was calculated using the comparative slaughter method. At 28 d venous samples were taken for blood gas analysis and haematocrit and relative heart, lung and liver weights were recorded. 3. Populations A and C showed the highest growth rates combined with a low FCR and a higher ascites incidence. A low FCR in these stocks was attributable to low values for Hp. These stocks also had low PO2 and high pCO2 in venous blood at low ambient temperature compared with other stocks. Stock B, which exhibited the slowest growth rate and the highest FCR, was not susceptible to ascites and showed higher Hp and PO2 and pCO2 at low ambient temperature. Populations D and E were intermediate for almost all variables. Heart and lung weights were both increased at LT, while liver weight did not differ between temperature regimes. 4. Our results show that a high haematocrit is not necessarily linked with an increased susceptibility to ascites.

Performance and physiological variables in broiler chicken lines differing in susceptibility to the ascites syndrome: 2. Effect of ambient temperature on partial efficiencies of protein and fat retention and plasma hormone concentrations

1. Male broilers of 5 genetic stocks (A, B, C, D and E), selected in different ways for fast growth and low food conversion rate (FCR) and differing in sensitivity to ascites, were subjected to 2 different ambient temperature (Ta) step-down programmes: normal (HT) and low (LT) Ta. 2. Ascites incidence was followed daily. Growth and food intake were measured weekly. Heat production (Hp), oxygen consumption (Oxc) and energy- metabolism parameters were calculated according to the comparative slaughter method. At week 4 blood samples were taken for the analysis of plasma T4, T3, growth hormone (GH) and insulin-like growth factor-I (IGF-1) concentrations. 3. Within-line changes of GH and IGF-1 point to the relative independence of both hormone concentrations. 4. Partial protein efficiency was higher in lines with lower GH, especially at LT. 5. The increase in plasma T3 concentration at LT was accompanied by a decrease in relative fat deposition from the increased energy expenditure. 6. The combination of fast growth and low FCR, linked to a low plasma T4 concentration at LT is indicative of a thyroid insufficiency which is related to an increased occurrence of ascites in these lines.

Evidence of mitochondrial dysfunction in broilers with pulmonary hypertension syndrome (Ascites): effect of t-butyl hydroperoxide on hepatic mitochondrial function, glutathione, and related thiols

The purpose of this study was to assess mitochondrial function and glutathione (a mitochondrial antioxidant) in response to oxidative stress in mitochondria in vitro obtained from broilers with and without pulmonary hypertension syndrome (PHS). Liver mitochondria from Control and PHS broilers were incubated with 0, 1, and 5-mM tertiary-butyl hydroperoxide (tBH). Indices of mitochondrial function [the respiratory control ratio (RCR) and the adenosine diphosphate to oxygen ratio (ADP:O)], and levels of mitochondrial and extra-mitochondrial reduced (GSH) and oxidized (GSSG) glutathione, cysteine, cystine, glutamate and cysteinyl-glycine were determined following tBH treatment. Lower RCR and ADP:O values were observed in PHS mitochondria than in controls. Whereas control mitochondria remained coupled (RCR > 2.0), only 3 PHS preparations remained coupled after 60 min of incubation with 5 mM tBH, indicating a greater susceptibility to oxidative stress in PHS mitochondria. The lower RCR in PHS mitochondria was due to increased oxygen consumption during State IV respiration. Oxidative stress following tBH treatment (decreased GSH and increased GSSG) was observed, but there were no differences in GSH or GSSG between control and PHS mitochondria. The PHS mitochondria did exhibit elevated mitochondrial and extramitochondrial cystine than controls, however. The results indicate that PHS mitochondria do not lack antioxidant protection from GSH, but lower RCR and ADP:O ratios in PHS mitochondria indicate a dysfunction that may contribute to the pathophysiology of this metabolic disease in broilers.

Susceptibility of broiler chickens to hemorrhages in muscles: the effect of stock and rearing temperature regimen

In this study, the effect of genetic constitution (stock) and rearing temperature on the occurrence of hemorrhages in thighs and breasts of water bath stunned broilers was investigated. Particular attention was given to the relation between the susceptibility for hemorrhages, body composition, and adaptations in blood variables induced by low rearing temperatures. A factorial experiment was performed with five parental stocks, differing with respect to growth rate, feed conversion, and body composition, and two temperature regimens (thermoneutral and below the zone of thermoneutrality). Hemorrhage scores in thighs were dependent on rearing temperature, not on stock, and were highest in broilers reared at low temperatures. In all stocks, high scores in the thighs were accompanied by an increased carbon dioxide pressure and bicarbonate and triiodothyronine concentration of the venous blood, and by an increased relative heart weight, hematocrit, and blood loss at slaughter. Hemorrhage scores in breasts were dependent on stock, confounded with day of scoring. An effect of rearing temperature was present only for the leanest, slow-growing stock having the lowest feed conversion ratio at thermoneutral rearing conditions. Scores in breasts were related neither to body composition nor to metabolic and hemodynamic adaptations to low rearing temperatures. It is concluded that high hemorrhage scores in thighs are related to hemodynamic and metabolic adaptations to an increased need for energy and oxygen caused by low rearing temperatures. Hemorrhage scores are not related to stock-dependent differences.

Intermittent lighting reduces the incidence of ascites in broilers: an interaction with protein content of feed on performance and the endocrine system

An experiment with 840 day-old male broiler chicks (Ross) was initiated to investigate the effect of intermittent lighting schedules, combined with two isocaloric feeds differing in protein content, on ascites mortality. At 9 d of age, chicks were randomly distributed over two rooms: one room with a 23 h light(L):1 h dark (D) lighting schedule (CL), and another room with an intermittent lighting schedule (IL, 1L:3D). In each room, two isocaloric feeds differing in CP content, supplemented or not supplemented with 1.5 ppm triiodothyronine (T3), were provided. The experiment was repeated under identical conditions except that lighting schedules were changed between rooms. From Day 14 onwards, biweekly growth and feed intake were determined and feed conversion (FCR) was calculated. Daily mortality was recorded and necropsies were performed. Weekly blood samples were taken from 10 randomly chosen birds per experimental group for measurements of growth hormone (GH), thyroid hormones [thyroxine (T4) and triiodothyronine (T3)], and hematocrit values. Birds reared in IL manifested a more concave growth trajectory than those in CL, which was associated with a lower FCR and higher plasma GH levels during the finisher period. Mortality due to ascites was markedly increased by dietary T3 supplementation. In hyperthyroid chickens, ascites mortality was lower in IL than in CL and lower in birds fed normal protein than in those fed subnormal protein levels. Dietary T3 decreased plasma GH and T4 levels, whereas T3 levels were increased. It is concluded that IL or a higher protein content of the feed reduces the incidence of T3-induced ascites mortality. Possible causal mechanisms are discussed.

Increased sensitivity to triiodothyronine (T3) of broiler lines with a high susceptibility for ascites

1. In the studies reported here, broiler lines divergently selected for susceptibility to ascites under low temperature conditions were tested for their sensitivity to 3,3',5-triiodothyronine (T3) with respect to growth rate, rate of mortality, plasma concentrations of T3, right ventricular hypertrophy (RVH) and incidence of ascites. 2. Mean body weight of the ascites-susceptible line (BC-line) was higher than that of the ascites-resistant line (A-line). Adding 0.5 mg T3/kg of the diet depressed growth rate to the same extent in both lines. The effect of T3 on growth was more pronounced for males than for females. 3. T3-supplementation increased the relative weight of the heart and the incidence of RVH to the same extent in both lines. More of the T3-treated BC-line chickens had fluid accumulation in the abdominal cavity than the T3-treated A-line chickens. 4. Dietary T3-treatment depressed the plasma concentration of growth hormone (GH) profoundly and insulin-like growth factor (IGF-I) slightly but to the same extent in both lines. The coefficient of variation of GH concentrations indicate that T3 treatment mainly decreased GH-pulsatility in young growing broilers. 5. Higher doses of dietary T3 (1 and 2 mg/kg) increased mortality in a dose-dependent manner. With 2 mg T3/kg, mortality in the BC-line was almost double that in the A-line. 6. These studies indicate that the development of ascites could be linked with thyroid function. Moreover, dietary T3 supplementation could be used to help identify ascites-inducing factors or genetic lines with differential sensitivity for ascites.

Comparison of energy metabolism during the growing period in quail lines selected for body weight

1. The present study was conducted to compare body weight, daily weight gain, relative growth rate, food intake, food conversion efficiency, abdominal fat weight, thyroid weight, plasma T4 concentration, body temperature, oxygen consumption, carbon dioxide production and heat production among three Japanese-quail lines selected for body weight: a random bred line (RR) and lines for large (LL) or small (SS) body weight. 2. T4 concentration increased in the order SS, RR, LL in both sexes and did not vary significantly between sexes; the SS line had a significantly higher value than that of the LL line. 3. The body temperatures of SS, RR and LL lines were 42.45, 42.03 and 41.25 degrees C in males, and 42.7, 42.03 and 41.63 degrees C in females. 4. The oxygen consumptions of SS, RR and LL lines were 63.4, 46.0 and 43.8 ml/kgW0.75 min. in males, and 61.4, 44.8 and 37.2 in females. The value for SS was significantly higher than those of RR and LL lines in both sexes (P < 0.01). The carbon dioxide productions of SS, RR and LL lines were 31.8, 33.8 and 27.3 ml/kgW0.75 min. in males, and 31.2, 31.9 and 27.3 in females. In both sexes, that of the LL line was significantly lower than those of the SS and RR lines (P < 0.01). 6. The heat productions of SS, RR and LL lines were 1.178, 0.994 and 0.842 kJ/kgW0.75 min. in males, and 1.142, 0.879 and 0.736 in females. In both sexes, the heat production of the SS line was higher than those of the RR and LL lines (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)