TECHNICAL ARTICLES Broilers/Layers/Breeders

Broiler Uniformity

The objective of the broiler farmer is to produce a well grown, uniform flock of broilers, at the least possible cost. In this equation flock uniformity plays an important role in maximising the returns. Too often the farmer complains that 80% of his flock is at 1.8kg while 20% is just 1.4kg. On a flock of 1 000 birds this farmer has lost 80kg of liveweight.

What is a uniform flock?

In a normal flock approximately 75% of the males and 78% of the females should be with l0% of the average weight for each sex for the flock to have satisfactory uniformity. As the male weight is higher, the variability of weights among males is higher. But many flocks do not attain this degree of uniformity, while others are better.

  • What factors are responsible for lack of uniformity?
  • When exactly does it start?
  • How can it be prevented?

Ten Factors Causing Lack of Uniformity

1. Male and female differences
2. Uniformity of chick weights on receipt
3. Early dehydration
4. Improper brooding temperature
5. Lack of ventilation
6. Selective feeding
7. Overcrowding
8. Insufficient feeder and water space
9. Feed quality
10. Disease

The majority of these factors are within the farmer’s control.

When does it start?

Lack of uniformity starts within a few hours of the chicks being put into the brooding area. The modern broiler reaches a weight of approximately 2.0 kg in 6 weeks. To achieve this the initial chick weight should triple or better during the first week of brooding. At this rate of growth, a uniformity problem can get rapidly worse and must be attended to as soon as it is recognised.

Achieving Uniform Flocks

A brief consideration of the factors causing lack of uniformity will help the farmer to identify his problems and take action to improve his flock uniformity.

1. Male and female differences

Nature has made male broilers capable of achieving 150 to 200 grams more liveweight than females by 6-7 weeks of age. Nature also ensures a roughly 50/50 ratio between males and females.

Farmers sometimes complain that they have received more females and fewer males. It must be understood that no hatcheries sex their broiler hatches unless specifically asked to do so. In the fast growing hybrid broiler it is sometimes difficult to distinguish the males from the females, as the early comb growth is very slow.

The natural lack of uniformity of 5-8% can be reduced in slow feathering broiler breeds by feather sexing and separate sex rearing on receipt of the chicks at the farm. This is particularly advantageous in large flocks reared at high stocking densities, where the separately reared males can be harvested at five weeks, giving more space for the females during the sixth week.

2. Uniformity of chick weights on receipt

Where large flocks of broilers are ordered it is not always possible for hatcheries to supply them from eggs of the same flock. Differences in egg weights will result in differences in chick weights. Separate brooding of different chick sizes received from the hatchery is the first step in achieving flock uniformity.

3. Early dehydration

Where chicks are received after a long transit period, particularly in hot climates , they are easily dehydrated. Over 70% of the chick weight is water and dehydration can reduce their weight significantly. The chicks must receive water (preferably with vitamins added) immediately on arrival. It is important that all chicks drink immediately. The chicks that receive water after a delay will suffer an early setback and lack of uniformity will be observed in a couple of days. In order to ensure that all chicks receive water immediately four practices are recommended.

  • Dip the beaks of weak chicks in water before placing into the brooding area.
  • Activate nipple drinkers with a broom where applicable.
  • Make sure water is available ie. the right height for the chicks. Remember a day old chick in winter is more likely to want warmth than cold water. If water is not very visible chicks will not drink.
  • Allow water to reach brooder temperature before arrival of the chicks.

4. Improper brooding temperature.

Correct brooding temperature at litter level is vital to get the chicks off to the best possible start. Brooders should be started 24 hours before the chicks arrive. The temperature should be 30°C to start with, reducing by approximately 1°C every 2 days. The temperature must be evenly distributed over the chicks. If this is not achieved some chicks (usually the marginally smaller ones) are chilled, start huddling and lose weight resulting in an early lack of uniformity. Floor temperature is critical during the initial brooding phase.

This temperature should be as close to the air temperature as possible and thermometers should be recording temperature at chick level. Floor temperatures which are too low will result in poor chick activity and contribute to poor uniformity. As well as absorbing moisture, the litter material also acts as an insulator. It is important that litter material is at least 150mm deep in the brooding area.

5. Lack of ventilation

When chicks are brooded together, the carbon dioxide and ammonia released has to escape and fresh air must be brought in. This may be achieved by opening the upper part of the curtains to allow proper ventilation. Early exposure to ammonia can seriously damage the respiratory system causing secondary infections later. Some chicks are more affected than others resulting in lack of uniformity. A good amount of fresh air bringing enough oxygen for growth is essential.

6. Selective feeding

By instinct chicks pick up larger and more palatable particles of feed. The practice of starting chicks on mash must be carefully evaluated as this may lead to selective feeding. Consequently, the chicks get an unbalanced diet resulting in poor uniformity. Chicks should be started on broiler starter crumbles.


Farmers are often tempted to increase the number of birds reared in a given size of house. Overcrowding is a short-sighted policy, as it not only creates competition for floor space but for feeder and water space as well. It also reduces the amount of fresh air available in the shed. Any competition for space will affect flock uniformity. The weaker birds will suffer and the farmer will lose money. Overcrowding will also cause stress to the birds,and E.Coli organisms which are commensal organisms of the intestine will flare up, leading to complex diseases, which also affect flock uniformity.

Ensure that broilers are not overcrowded in the brooding period. As a starting point, 40 chicks per square meter is sufficient up to about 5 days. Thereafter increase the area regularly giving the whole house not later than 21 days in winter and 14 days in summer.

8. Insufficient feeder and water space

Traditionally farmers have been providing two tube feeders per 100 birds. This may have been satisfactory for the relatively slow growing broiler 10 years ago. However todays broiler needs to have full access to feed at all times. All birds should be able to eat from the feeders at the same time. Experience has shown that with a minimum of three feeders per 100 birds the results in terms of body weight and uniformity are outstanding. The increased initial investment can be recovered in a few flocks. Water is the most important nutrient particularly in hot climates.

Any competition for water space will result in the weaker birds getting dehydrated and poor of uniformity ensues. Ensure that at all times all birds have access to cool and clean drinking water. Bell drinkers should be supplied at 1/100 birds (minimum) or 12 birds per nipple post brooding. Access to feed and water at an early stage is vital. Ensure a minimum of one chick fount per 100 chicks or 30 chicks per nipple, as well as one scratch pan per 100 chicks.Where nipples are used from the start, make sure that the pressures are low enough for the chicks to activate the nipple. The use of paper to feed onto is encouraged and a rule of thumb approximately 30% of the initial brooding floor area should be occupied by feed.

9. Feed quality

A farmer might have the best-feed formulation in the world. This is of no use unless he is able to procure quality ingredients, grind them to the correct size and mix them just right. Feed manufacturing is an art and a science, and is best done by experts. Poor feed quality arising from any of the above factors will result in an unbalanced diet, selectively feeding and perhaps disease. These are factors that can seriously affect uniformity and growth.


Any disease can ruin the uniformity of the flock. While the chicks may leave the hatchery healthy, disease particularly respiratory infection can strike right from the transportation period onwards. Multiple age group rearing in the same farm multiplies the chance of disease. It must be understood that while a disease may be obvious in 20% of the flock, most of the other birds are fighting the infection in subclinical form. Disease affects different birds to different degrees, feed and water consumption drop, weight gain stops or even reduces and the flock is generally rendered unprofitable.

Prevention of the disease is better than cure and all-in-all-out rearing, biosecurity and proper nutrition and vaccination programme can prevent most diseases. A liveability of 98% must be aimed for and anything lower means one needs to check the efficiency of the disease prevention programme.


Keith J. Rosario – Poultry International August 1999.

Date published: 2003-10-20

Tim Nixon

Poultry International