High stocking density may be associated with a surge in air- borne patho- gens, which cause disease problems and poor production performance of overcrowded chickens.

protein, fat, and carbohydrates and hence affects the use of these nutrients for growth and other biological functions.

Skin and feather cover Increased stocking density has, in many cases, resulted in in- creases in dermatitis, skin lesions and scratches. Feathering also begins to deteriorate at a density of 30 kg/m², probably due to increased feather pecking and the degree of litter cak- ing, which reduces the chance for dust bathing behavior and hence prevents birds from keeping their feathers clean and free of parasites. This may be part of the reason for the in- creased number of scratches observed in birds housed at higher stocking densities. Stocking density, the strain of birds, and the degree of feathering could all be considered as po- tential risk factors for abdominal scratches in broiler chickens. A significant increase in the incidence of breast blisters in fe- males, with a similar trend for males, has been demonstrated in birds reared at high stocking densities.

Diseases The increased stocking density may lead to increased levels of airborne dust and hence more respiratory diseases and can lead to the incidence of other disease problems such as as- cites and contact dermatitis. It was also found that high stock- ing density resulted in adrenal hypertrophy, suggesting that birds at high stocking densities may be im muno com prom-

36 ▶ ALL ABOUT FEED | Volume 28, No. 8, 2020

ised. This is probably the cause of the reduced immune re- sponses observed at high stocking densities. Birds housed at lower stocking densities (10 or 14 birds/m²) had a greater an- tibody response to Newcastle disease than birds housed at 18 birds/m².

Economics Increasing stocking densities in broiler production is usually done to maximise economic returns from a production unit, but this objective may not always be achieved. There is an optimum stocking density that will maximise economic re- turns, but this varies, depending on the environmental con- ditions and management of the birds. Birds raised at high stocking densities must receive adequate feeder and drinker space. Proper ventilation and cooling systems should also be provided to reduce temperature, CO2

, and ammonia levels

which affect growth and health performance. In this case, the stocking density can be increased from 10-12 birds/m² to 15-17 birds/m², thus increasing the total capacity of the farm by about 30% with no detrimental effects on performance. From an economic standpoint, the increased farm capacity with feeder/water space, ventilation, and cooling systems would cost only 40% of the funds needed to establish a new poultry house.

References are available from the author on request.

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