VENTILATION IN POULTRY HOUSE
High ambient temperature and humidity adversely affects poultry production. The poultry farmer can do much so as to positively influence bird performance during heat stress through a combination of proper feeding strategies.
Current requirements for ventilation in a poultry house are close to ideal, but not as close as possible. The finesses of optimal ventilation is in the key which is not to ventilate according to the weight of birds (amount of kilos) in the house, but ventilate according to metabolic weight and take the effects of wind chill into the equation.
Research has shown that there is a lot to gain with proper ventilation. The metabolic weight of small chicks is about double of the actual weight. When the chicks weigh in at around 1 kilogram (kg) the metabolic weight is equal to the real weight and above 1 kg the metabolic weight is a little lower. That means that minimum ventilation at the start of the round should be cranked up, while at the end of the round maximum ventilation can be somewhat reduced.
To make things even more complicated there is the effect of wind chill which according to Wageningen University the ideal temperature of the broiler is the absolute air temperature (as shown on a thermometer) + the relative humidity = 90. Above the value of 115 a broiler has serious heat stress, below 50 cold stress.
In practice that means that at 20○C and a humidity of 50% a broiler is cold. The other way around, at a comfortable 20○C at humidity of 90% the bird has serious trouble to loose body heat unless wind speed is added to the equation. An air current of 1m/sec at 35○C degrees and a humidity of 50% can chill up to 10 degrees.
Nutritional management of heat stress
Timing of feeding is an important factor in alleviating heat stress effects on feed intake and utilisation. Therefore, the major part of the diet should be made accessible to the birds at times of relatively low temperature (early morning and late evening) with the remaining part thereof to be made available all the time.
Broiler chickens appear to be more responsive to the timing of feeding than laying hens. In most cases, the proper timing of feeding could by itself alleviate many of the problems associated with heat stress in broilers, but have not been an adequate measure for layers. It is, therefore, suggested that other feed management factors should also be considered in this latter case for better laying performance. For example, feed should always be fresh and not be stored for longer than two months, especially in summer to reduce the possibility of mycotoxin build up.
Furthermore, feed should be properly processed (crumb, pellets, or mash), with extra feeders to be provided in order to encourage appetite on hot days. It might also be of benefit to dim the lights while feeding, in order to reduce activity and hence minimise heat load on the birds.
Raising the nutrient intake during heat stress, by changing the feed specification, may have a detrimental effect on survivability, but increasing the digestibility of nutrients and the use of specialist micro ingredients has been shown to have benefits. The principle nutrients to consider are:
Proteins and amino acids: nutrient digestibility should be increased rather than nutrient density, minimise excess protein and balance amino acids and minimise the crude protein level in the diet.
Vitamins and minerals: certain vitamins are known to have a positive effect on the birds’ response to heat stress including Vitamin E, D, A, C, B2 and nicotinic acid. Under no circumstances should vitamins be withdrawn from the diet.
Energy: the diet should be supplemented with fat rather than carbohydrate. Increasing the energy density of the diet will increase growth rate but will also increase heat output.
As temperature increases, the bird has to maintain the balance between heat production and heat loss, and so will reduce its feed intake. Trials indicate that feed intake is reduced by 5% for every 1○C rise in temperature between 32-38○C.
Reduced feed intake is the main cause of poor performance. As a general rule, for each 2.5°C (5°F) increase in house temperature above 29°C (85°F), the energy content of the feed should be reduced about 22kcal/kg (10 kcal/lb).
The feed energy content can be decreased because more of the energy requirement of the bird can be met by the increase in environmental temperature. As the total amount of energy in the feed is decreased, the proportion of the total feed energy provided by added fat should be increased. The addition of fat may, in certain instances can be as high as 4.5% of the ration. This may require the use of low-energy feed ingredients such as wheat offals and/or soy mill feed (soy hulls). A by-product of the digestion or metabolism of feed is the production of body heat (heat increment).
It is widely recognised that fat has the lowest heat increment of the energy nutrients — i.e., carbohydrate, protein, and fat. In comparison to proteins and carbohydrates, the digestion of fat results in less production of body heat per calorie of feed energy. The heat load of the bird can be reduced by replacing other dietary energy with dietary fat. Generally the energy content of the feed should be reduced gradually in increments of 22-33 kcal/kg (10-15 kcal/lb). Calorie reductions of this magnitude can be made at least twice each week.
When the nutrient density of the formula is increased to compensate for the reduction of feed intake, the protein content of the feed may, in some instances, be reduced by about 0.50% below the calculated value. If this is done, the intake of the needed amino acid can be optimised by providing increased quantities of synthetic amino acid such as methionine and lysine.
Adjusting the intake of protein is important because the body heat produced by protein digestion or metabolism is, as noted earlier, the greatest among the energy nutrients — i.e., carbohydrate, fat, and protein. Restrict the intake of feed about three hours before temperatures are expected to exceed 36°C (95°F) for more than three hours. Adjust the lighting schedule to encourage the consumption of feed in the night and early morning. A midnight feeding or an intermittent lighting programme can encourage feed consumption at night. Vitamin C in the ration (50-300 gm/tonne of feed) can protect birds from the effects of heat stress and enhance the survival of birds exposed to acute heat stress.
Water supply
Heat-stressed birds can dissipate over 80% of their heat production via evaporative cooling. The evaporative heat dissipation extent and calories dissipated per breath are correlated with water consumption level and balance. With reduced water temperature, water consumption would be encouraged, thereby increasing evaporative cooling and heat dissipated per breath. Studies have shown that increasing water consumption by 20% over the basal level can increase heat loss per breath by as much as 30%, with a resulting improvement in performance. The improved performance in this case could be attributed mainly to the increased feed intake to offset a portion of the hypothermic effect, and partly to the improved wellbeing of heat-stressed birds
Water consumption could also be increased by using water troughs in place of nipple or bell-type drinkers, at least during the hot season. With such a system birds would not only be allowed to get enough water, but would also have the chance to submerge their heads and combs in water and hence reduce the heat load by evaporation of water from these body parts.
