Chickens die from heatwave

THE prolonged heat wave felt throughout the country over the past two months has culminated in increased broiler chicken mortalities at most backyard-run projects in urban areas.

Most town and city dwellers have over the years ventured into broiler-rearing projects for income generating or as a way of supplementing their salaries.

However, improper housing of the birds has seen most of the farmers losing out in the event of unfavourable weather conditions especially cold and heat. Climatic factors may cause production losses in broiler production. Many of these losses are caused by heat waves, which increase broiler mortality and reduce their productive performance.

Mr William Marko, a broiler chicken farmer in New Luveve high density suburb in Bulawayo said he lost 10 birds on Christmas day due to the heat wave that spread across the southern parts of the country with temperatures soaring over 34 degrees.

"We lost a total of 10 chickens in one day. The heat wave on Christmas day was excessive. I am afraid if it continues like this, we will have a big problem. These chickens are delicate and they need specific climate environments," he said.

The expression of heat stress in poultry production can be described as "acute" or "chronic". Acute heat stress refers to short and sudden periods of extremely high temperature, whereas chronic heat stress refers to extended periods of elevated temperature. Chronic heat stress has detrimental effects on the performance of broiler birds reared in the open sided poultry houses; principally through reducing feed intake, growth rate, negatively affect feed efficiency and carcass quality as well as health.

Matabeleland North provincial veterinary officer, Dr Polex Moyo said it was difficult to maintain high production levels for poultry farmers due to the fatal heat wave forecast.

"The environment of broiler chickens needs to be controlled all the times. It is a huge task to keep the required temperatures inside a fowl run. Chickens need proper ventilation systems. These type (broiler) of chickens are delicate and need to be treated with care.

"Poultry farmers need to thoroughly put in place foul runs that are spacious and positioned in an environment friendly for the birds. However, the mortality of the chickens is not a big issue because in some instances the person responsible for the upkeep will not be fully equipped with knowledge of keeping the chickens," Dr Moyo said.

Attempts have been made at reducing heat stress mortality in broilers by acclimatisation. Raising house temperature prior to the onset of a heat wave has been shown to reduce mortality. This is partly due to the reduction in feed intake in response to the stress.

Besides energy, consideration must be given to the amino acid balance of the diet during heat stress. If the energy content of the diet is increased, all other nutrients must be increased proportionally. Minimising excess amino acids usually improves feed intake. During hot periods, lower protein diets supplemented with limiting amino acids is advised. Today's broilers are selected and managed with the aim of increasing meat yield and decreasing fat deposition.

Sensible heat loss refers to heat dissipated through heat transfer from the broiler to the surrounding air. If the air is cooler than the broiler's surface temperature, heat flows from the broiler to the surroundings. If the air is warmer than the broiler's surface temperature, broilers will not be able to dissipate heat and heat stress will occur.