Western
Meeting of Poultry
Clinicians and Pathologists
|
Clinicians and Pathologists
|
|
Ascites Update R.J. Julian Ontario Veterinary College
Pulmonary hypertension (PH) is increased pressure in the pulmonary arteries and other vessels in the lung. PH increases the workload on the right ventricle (RV) resulting in right ventricular hypertrophy (RVH). RVH is followed by valvular insufficiency. The most frequent cause of ascites in meat-type chickens in increased blood pressure in the liver and portal system as a result of valvular insufficiency and right ventricular failure (RVF). The marked increase in ascites in broilers at low altitude is caused by pulmonary hypertension syndrome (PHS). PH occurs because there is not enough space for blood-flow through the lung to supply the oxygen that fast-growing meat-type chickens require for metabolism and growth, so the FV has to apply more pressure to pump blood through lung-PHS can be caused by increased blood-flow or increased resistance to blood-flow in the lung. Things that increase blood-flow or increase resistance to flow are additive. Ascites caused by PH is a metabolic or production –related disease. It occurs as the result of the continuing increase in growth rate on a small body frame that has too little lung and air sac volume for its metabolic needs. Anything we can do to slow blood-flow (lower oxygen requirement) or make blood-flow easier will reduce ascites. Cold and moderate heat both increases the oxygen requirement and the incidence of PHS. We know that slowing growth rate will reduce the incidence of PHS at both high and low altitude. Severe feed restriction such as skip-a-day feeding will stop deaths from PHS, but other feed restriction will reduce ascites as well (Julian, Avian Path., 22: 419-453, 1993). Scolsberg et al. (Avian Dis 35:681-684, 1991) reported reduced ascites with restriction to 20 g feed/bird/day between days 6 and 11 with improved feed conversion. Suarez and Rubio (Vet Mex 20:193-195, 1989) observed a marked reduction of ascites at high altitude by restricting access to feed to 11, 9, or 7 hours from days 14 to 42 (broilers grown to day 53). Body weight was reduced, but feed conversion improved at 9 and 7 hours. Dietary animal fat and by-product (particularly chicken by-product) increase the oxygen requirement. Urease inhibitor in the feed (Poul Sci 73 (Supp 1) Abst Nos 8, 9, 10, 11, 1993) may reduce ascites by lowering metabolic oxygen requirement. RBC has to fold or roll up to go through the capillaries of the lung. The RBC of broilers is more rigid than those of Leghorns. Lack of oxygen increases this rigidity. Increased rigidity increases the resistance to blood-flow. High dietary salt also increases RBC rigidity. High dietary salt also causes mild lung edema that interferes with oxygen exchange and increases resistance to blood-flow and salt increases metabolic oxygen requirement and blood volume, which increase blood-flow (Mirsalimi et al., AJVR, 53: 2359-2363, 1992; Avian Path, 22: 419-454, 1993). Vitamin C may make blood-flow easier by making RBC more deformable. Hypoxemia causes the body to produce more red blood cells (RBC). This makes the blood more viscid which increases the resistance to flow. A survey of broiler barns in Ontario in the winter showed that the oxygen level is not low, however the oxygen level in the blood of fast-growing broilers is low whereas slow-growing broilers from the same flock are normal (Julian, Av Dis 36: 730-736, 1992). Fast-growing broilers may have low blood oxygen because of abdominal mass restricting air sacs and breast muscle mass restricting breathing. An excess of nutrients with a negative charge could cause acidosis and reduce the ability of the hemoglobin to pick up oxygen. Low blood oxygen would stimulate RBC production and makes the blood more viscid. There is no evidence yet that lack of oxygen in the incubator and hatcher causes ascites in broilers at low altitude.
|
|
To send us your comments or questions regarding this web site, click here. |