R. J. Julian

Ascites in poultry

Research on ascites occurring in meat-type chickens reared at moderate and low altitude has shown that the pathogenesis is similar to that of the high altitude disease. Pulmonary hypertension (PH) caused by increased blood flow or increased resistance to flow in the lung results in right ventricular hypertrophy (RVH), valvular insufficiency, increased venous pressure and ascites. The structure of the avian heart, with its thin-walled right ventricle and muscular right atrioventricular valve, allows PH to induce heart failure quickly. The sudden increase in pulmonary hypertension syndrome (PHS) in meat-type chickens in the 1980s was associated with a rapid increase in growth rate and feed conversion. This was a result of a combination of genetic selection for fast-growing, heavy broilers with low feed conversion and a more dense, high caloric, pelleted food that supplied all the nutrients required for rapid growth and encouraged a high nutrient intake. PHS in meat-type chickens is usually primary pulmonary hypertension, that is, PH that occurs without evidence of prior heart or lung disease that could account for the increase in blood flow or resistance to flow that results in the increased pressure in the pulmonary arteries. The lungs of birds are firm and fixed in the thoracic cavity and they do not expand to draw air into the lung. The blood and air capillaries form a rigid network that allows only minimal expansion of the blood capillaries when more blood flow is required. Air is moved through the lung by abdominal movement which draws air in and out of the air sacs. The anatomy and physiology of the avian respiratory system are important in the susceptibility of meat-type chickens to PHS. The small stature of the modern meat-type chicken, the large, heavy breast mass, the pressure from abdominal contents on air sacs, and the small lung volume compared to body weight, may all be involved in the increased incidence of PHS. There is limited space for blood flow in the avian lung. Factors that increase blood flow or increase resistance to flow are additive. Increased blood viscosity caused by the polycythaemia of hypoxia, or increased erythrocyte rigidity of high Na (+), are more likely to produce PH in fast-growing than in slow-growing birds. Increased flow due to cold exposure is also additive. Ascites caused by PH is a production-related disease at low altitude. It can be prevented easily by restricting growth rate. It is possible that some meat-type chickens of the phenotype we have created have reached the limit of blood flow through their lungs and that future improvements in growth rate will only be possible if the lung and abdominal cavity capacities are enlarged.

The effect of cold and dietary energy on right ventricular hypertrophy, right ventricular failure and ascites in meat‐type chickens

Male progeny from two commercial sire strains, were fed on a high energy or low energy diet and kept at an environmental temperature of 23 C or 13 degrees C after day 22 to day 57. In the cold 42.4% of strain A and 29.6% of strain B died from right ventricular failure (RVF) and ascites secondary to pulmonary hypertension (PH) prior to day 57. Of the birds surviving to day 57, 9.4% (strain A) and 6.4% (strain B) had RVF and ascites. In the warm, 17.3% (A) and 7.4% (B) died from RVF and ascites before day 57 and 4.6% and 3.2%, respectively had ascites at day 57. Chickens on the high energy diet were significantly heavier at day 56 than those on the low energy diet, particularly those kept in the cold. However, chickens on the latter diet had better weight gain between days 42 and 56, again more marked in cold conditions. The higher metabolic rate elicited by cold would increase oxygen consumption and blood flow in these broilers which, because of their rapid growth, already had a high metabolic rate. The cause of PH was probably insufficient pulmonary vascular capillary capacity for the blood flow necessary to meet their metabolic oxygen requirement.

Lung Volume of Meat-Type Chickens

Lung volume (LV) in meat-type chickens was measured by water displacement and was computed as a percentage of body weight (BW). The percentage of LV/BW declined from 2.02 +/- 0.190% at day 1 to 1.38 +/- 0.163% at day 144. Pulmonary hypertension caused by insufficient lung capillary capacity or oxygen exchange area results in right ventricular failure and ascites in meat-type chickens. Insufficient LV in very fast-growing broilers may contribute to this problem. Selection procedures in meat-type chickens should include a method for estimating LV.

Individual and combined effects of t‐2 toxin and das in laying hens

1. The individual and combined effects of T-2 toxin and 4,15-diacetoxyscirpenol (DAS) on laying hens were investigated in an experiment consisting of a 2 x 2 completely randomised factorial design with dietary concentrations of 0 and 2 mg/kg T-2 toxin and 0 and 2 mg/kg DAS. 2. Individually, T-2 toxin and DAS induced oral lesions in half of the hens and decreased significantly egg production and food intake. 3. The effects of T-2 toxin and DAS were additive for reduced food consumption and incidence of oral lesions. However, a synergism for reduced egg production was observed during the last experimental period. 4. No effects on body weight were observed during this study. Mild changes in selected plasma enzymes activities and no change in liver malondialdehyde content were detected. 5. The combination of T-2 toxin and DAS was more toxic than the single mycotoxins, for some parameters, and therefore, may pose a greater economic threat to the poultry industry than either of the toxins individually.

Effect of Hypobaric Hypoxia on Slow- and Fast-Growing Chickens Fed Diets with High and Low Protein Levels

The occurrence of pulmonary hypertension syndrome in fast-growing broiler chickens and slow-growing leghorns was studied. In two similar trials, broiler chickens and white leghorns were placed either at low altitude (295 m) or in hypobaric chambers (simulated high altitude of 2054 m) and fed either a high- (22%) or low-protein (17%) ration. Right ventricular hypertrophy as measured by right-ventricle:total-ventricle (RV:TV) weight ratio was used as an indicator of pulmonary hypertension. The leghorns did not develop pulmonary hypertension as the result of polycythemia induced by simulated high altitude. Compared with low-altitude broilers and leghorns, broilers reared at high altitude responded with significantly higher hematological values and 56% ascites mortality because of right ventricular failure from pulmonary hypertension, as measured by an increased RV:TV ratio.

The use of selected plasma enzyme activities for the diagnosis of fatty liver-hemorrhagic syndrome in laying hens.

Profiles of plasma enzymes were compared in two strains of single comb white leghorn laying hens, a normal commercial strain and strain UCD-003, which is highly susceptible to fatty liver-hemorrhagic syndrome. Plasma activity of lactate dehydrogenase (LDH), glutamate dehydrogenase (GDH), aspartate aminotransferase (AST), alanine aminotransferase (ALT), and creatine kinase (CK) averaged 194 +/- 27, 4.0 +/- 2.8, 146 +/- 20, 1.0 +/- 1.0, and 1041 +/- 268 U/liter, respectively in normal birds. Activities of LDH, GDH, AST, and ALT, but not CK, were significantly higher in UCD-003 than in normal hens. A bimodal distribution of activities of all enzymes was found in the UCD-003 hens, with some birds showing activities comparable with those of the normal hens and others with values that were 2-10 times greater than those found in normal hens. These results are consistent with the extensive hepatic lesions observed in the UCD-003 strain of birds. Average gross hemorrhagic scores from visual inspection (scale of 0-3) were 0.28 +/- 0.45 in normal birds and 1.63 +/- 0.94 in the UCD-003 birds. Even though no clear relationship was found between plasma enzyme activities and the extent of liver hemorrhage in individual birds, the UCD-003 hens consistently had average values significantly higher for plasma enzymes that indicate liver damage. The results suggest that measurement of enzyme activities indicative of liver damage in birds, particularly AST, LDH, and GDH, is a valuable tool in the diagnosis of fatty liver-hemorrhagic syndrome in a flock of layers.

Cobalt-induced polycythaemia causing right ventricular hypertrophy and ascites in meat-type chickens.

Cobalt increases the red cell mass in both man and animals by increasing the production of erythropoietin. Since meat-type chickens can develop pulmonary hypertension from increased erythropoiesis and polycythaemia, two trials were conducted to investigate the role of cobalt on broiler chicken erythropoiesis and pulmonary hypertension. The results showed that feeding cobaltous chloride at 500 parts/10(6) to meat-type chickens from 1-day-old for 42 days significantly increased haemoglobin content and, to a lesser extent red blood cell count, and haematocrit. No effect was observed on mean corpuscular volume. Increased haemoglobin content was linearly correlated with pulmonary hypertension as measured by the right ventricle weight to total ventricle weight ratio (RV:TV). Levels of malondialdehyde in cardiac tissue were also correlated with the RV:TV ratio, suggesting that peroxidative damage may be related to ventricular hypertrophy. Chickens fed cobalt showed a significantly higher incidence of right ventricular hypertrophy and right ventricular failure and 18.3% developed ascites.

Effect of Hypoxia and Diet on Spontaneous Turkey Cardiomyopathy (Round-heart Disease)

The purpose of this study was to examine the effect of hypoxia-induced hypoxemia and rate of growth on spontaneous dilatory cardiomyopathy in turkey poults. Turkey poults grown in a hypobaric chamber at an atmospheric pressure of 592 mmHg (calculated partial pressure of oxygen: 124 mmHg; calculated altitude and O2 equivalents: 2054 m and 16.3%) on a rapid-growth diet developed a mainly right ventricular dilatory cardiomyopathy typical of the acute form of spontaneous turkey cardiomyopathy (STC). Poults grown in a hypobaric chamber on a slow-growth diet had a much lower incidence of STC. Control poults at atmospheric pressure, altitude 295 m (calculated atmospheric pressure: 735 mmHg; partial pressure of oxygen: 154 mmHg, 20.26% O2), on a rapid-growth diet had an incidence of STC similar to that of the slow-growth hypobaric group, while those on a slow-growth diet had a lower incidence.SUMMARY. The purpose of this studywas to examine the effect ofhypoxia-induced hypoxemia and rate of growth on spontaneous dilatory cardiomyopathy in turkey poults. Turkey poults grown in a hypobaric chamber at an atmospheric pressure of 592 mmHg (calculated partial pressure of oxygen: 124 mmHg; calculated altitude and 02 equivalents: 2054 m and 16.3%) on a rapid-growth diet developed a mainly right ventricular dilatory cardiomyopathy typical of the acute form of spontaneous turkey cardiomyopathy (STC). Poults grown in a hypobaric chamber on a slow-growth diet had a much lower incidence of STC. Control poults at atmospheric pressure, altitude 295 m (calculated atmospheric pressure: 735 mmHg; partial pressure of oxygen: 154 mmHg, 20.26% 02), on a rapid-growth diet had an incidence of STC similar to that of the slow-growth hypobaric group, while those on a slow-growth diet had a lower incidence.

Ascites in meat-type ducklings.

Hearts selected at random from the line at a duck processing factory gave a mean right ventricle to total ventricle (RV/TV) ratio of 0.188 (18.8% right ventricle). Ducks condemned because of ascites at the same factory fell into three groups: ducks with ascites secondary to right ventricular failure (RVF) with a RV/TV ratio of 0.336 (mean of 12 ducks), ducks with ascites secondary to hepatic amyloidosis with a RV/TV ratio of 0.202 (mean of 8) and ducks condemned as ascitic but in fact suffering from peritonitis with a RV/TV ratio of 0.202 (mean of 4). The results indicate that the most common cause of ascites in meat-type ducks at slaughter is RVF as it is in broiler chickens. The RV/TV ratio in normal ducks was less than 0.230; in ducks with ascites from RVF it was greater than 0.283.

Heritability of sudden death syndrome and its associated correlations to ascites and body weight in broilers

1. Genetic parameters for the sudden death syndrome (SDS) were estimated in meat-type chickens. Data were collected over 11 generations of selection for body weight within two distinct breeds (Cornish and White Rock). 2. The animal model was used exclusively with linear methods (LM) to estimate genetic parameters. Heritability (h 2) of SDS on the liability scale was 0·30 ± 0·002 and 0·25 ± 0·002 in the Cornish and White Rock breeds, respectively. 3. A positive genetic correlation (r g) with ascites (AS) was determined (∼0·3 ± 0·006). However, it was not possible to estimate the r g of SDS with body weight because of the low prevalence of the defect trait studied (1·8% in the Cornish and 1·5% in the White Rock). 4. Heritability of SDS calculated using male records only was 0·45 ± 0·009 and 0·35 ± 0·009, and r g with body weight was 0·30 ± 0·010 and 0·27 ± 0·009, in the Cornish and White Rock breeds, respectively. 5. In conclusion, the heart defect investigated was heritable with a positive genetic correlation with AS and body weight.