POULTRY PRODUCTION MANUAL
Chapter 3 - Avian anatomy and physiology
EXCRETORY SYSTEM
The main organ of the excretory system is the kidney. The functional units of kidneys are nephrons. The functions of the excretory system are to excrete water and metabolic wastes and to regulate the acid-base balance of the bird’s body.
The two kidneys of the domestic fowl each generally with three lobes are found immediately behind the lungs on each side of the vertebral column and closely associated with it (see Figure 3.19 below). They are brownish in color and their consistency is such that they are easily damaged during their removal. The kidneys are normally left in when a broiler carcass is processed.
Figure 3.19 - Photograph of the inside of the back of a chicken indicating the location of the kidneys of a chicken
Each kidney is divided into three distinct lobes. Chickens do not have a bladder. Urine passes from the kidney, through the ureters, which then empty into the cloaca. Chicken urine consists of yellowish fluid with a white pasty substance largely made of uric acid. Uric acid is the main product of nitrogen metabolism in birds and is not water soluble; this is why solids make up part of the urine.
The straight and narrow ureter is a tube that leaves the medial border of each kidney and opens into the cloaca adjacent to the deferent duct of the male or the oviduct of the female.
The primary component of poultry waste is uric acid, the major end product of protein utilization. Uric acid is a white, pasty substance. Poultry waste is comprised of urine and feces (see Figure 3.4 in the digestive system section, and shown below); these are not separate.
Figure 3.4 - Normal chicken manure showing the white uric acid crystals on the fecal material
As indicated in the discussion on the Circulatory system, birds have retained the more ‘primitive’ renal portal system, a feature not found in mammals. The renal portal system allows blood from the back portion of the body to flow to the kidneys via the iliac veins. There is a valve that allows blood to either pass on to the kidneys where nitrogenous wastes are removed, or return directly to the heart via the renal veins. Because of this renal portal system, drugs injected into the leg muscles may be toxic to the kidneys; usually it is better to inject into the large muscles of the chest.
Gout is a metabolic disorder associated with the kidneys. In gout the kidney function is slowed down to a point were uric acid accumulates in blood and body fluids. It can also leads to accumulation of white uric acid crystals in soft tissues of various organs. There are two types of gout – visceral and articular.
Visceral gout is a condition in which uric acid crystals are seen in soft tissues. The visceral form of gout is commonly found in broilers resulting in economic losses due to mortality and morbidity. The kidney damage can arise from infection with certain strains of Infectious Bronchitis, Avian Nephritis virus, exposure to some mycotoxins, or inadequate water intake. Residual toxic effects due to some of the disinfectants have also been reported.
Articular gout is a condition in which urate crystal deposits are seen in joints. This condition is rarely seen in broilers. Main causes are genetics and high protein diets.
