Avian Water Metabolism—A Review

SummaryWater represents about 70% of total body weight and is made up of intracellular and extracellular fluids and plasma. The metabolism and balance of body water is related to the maintenance of a dynamic equilibrium within and between these compartments.Water is obtained through drinking, is present in most feedstuffs and is also produced in the body as a by-product of some biochemical reactions. Drinking water represents some 70% of total water intake, while feed and metabolic water contribute about 10% and 20% respectively to this pool.Water is lost from the body via the faeces, as urine and through evaporative loss from the respiratory tract. Broiler chickens produce excreta containing 60–70% water while laying birds may excrete as much as 80% water in the faeces. As long as urine is hypotonic to extracellular fluid, water reabsorption will occur in the coprodeum and urodeum in the order of 25–30 ml/day for the adult fowl.Water is lost by evaporation from the moist surface of the respiratory tract to the inspired air which is saturated with water vapour at increased temperatures approximating that of the body. Evaporative rate is proportional to respiratory rate. As a means of water loss from the body, evaporation is correlated with environmental temperature; 50% of total heat loss may occur through evaporation at environmental temperatures around 35°C.That younger birds have a greater proportion of body water than mature birds may be related to increases in fat deposition with age and the fact that body fat and body water are negatively correlated. The rate of water turnover in the body is also greater in younger birds, as it is in the laying versus non-laying and the adult male bird.Body dehydration can occur as a result of either a reduced water intake or an increased water output from the body. Diarrhoea is the most common reason for excessive water loss.Restrictions in the quantity of water consumed by birds can drastically affect productive performance. With 48–72 hour periods of water deprivation, egg production may cease, while 20–50% restriction with broiler chickens severely influences feed intake: weight gain ratios. Turkey poults are most susceptible to dehydration resulting from drinking water deprivation while non-laying hens are least susceptible.Beneficial effects on production are proposed for the administration of hot or cold drinking water. Cold water may stimulate feed intake, thus helping to maintain egg production of laying birds housed under very high environmental temperatures. A saving in feed costs may result through the administration of heated drinking water, in situations of low environmental temperatures.