Balanced Loading of the Setter

5 July 2013, at 12:00a.m.

Balanced loading is key to preventing uneven temperatures inside the setter, which increases the risks of decreased hatchability and chick uniformity, writes Roger Banwell, Hatchery Development Manager at Petersime.

Sometimes, it is inevitable to load eggs from different flocks into one incubator. To avoid that this leads to uneven temperatures inside the setter and, consequently, decreased hatchability and chick uniformity, balanced loading is key.


In order to have optimum temperature, ventilation and humidity levels throughout the entire setter, hatchery staff should ideally be only loading the setters with fertile eggs from one single flock, that have been stored for the same period of time. These eggs will be about the same size, and will produce about the same amount of heat at about the same moment in time. In this case, the optimal incubation program can be used specifically for this batch of eggs.

However, in practice, setting only eggs from a single flock is not always possible to achieve. If not enough eggs from the same source are available to fill a machine, it is by no means an option to leave trolleys out and start an incubation cycle in a machine that is not fully loaded.

In such a case, it is inevitable to load eggs from different kinds of flock into one machine. However, if eggs from a highly fertile flock with little storage time are loaded on one side and eggs from a flock of low fertility with a lengthy period of storage on the other side, problems will occur. The first group of eggs will need less time to heat up and will produce heat faster, while the second group of eggs will heat up slower, start developing later and produce heat later. As a consequence, high temperature differences will occur. These differences will dangerously increase towards the end of the incubation cycle, as the eggs produce more heat and ventilation and cooling are increased. They will lead to a wide hatch window, possible heat damage and very poor chick uniformity.

In this article, Mr Banwell explains how you can load your machine with different flocks and at the same time avoid any losses in hatchability or chick uniformity. This can be done with the technique of balanced loading.

Advantages of Non-linear Weight Loss

In Petersime incubators, we apply the non-linear weight loss system. This allows for the environment to be extremely stable during embryonic development (days 0 to 9 for chickens): there is very limited intervention from ventilation, humidification and cooling. Balanced loading is not a key factor at this stage.

During the embryonic growth phase (days 9 to 18), heat production is such that a significant degree of cooling and ventilation is necessary, which will inevitably lead to some temperature differences. However, they will not be excessive; by applying non-linear weight loss, a natural build-up of humidity is enabled, so that no additional artificial humidity is necessary. This eliminates one major disruption in temperature uniformity as well as a possible contaminant to the bio-security of the setter.

When setting a mix of eggs, these reduced temperature differences can be used to our advantage by ensuring a balanced load.

Balanced Loading

Balanced loading means setting a mix of eggs while taking into account their level of heat production and the point in time at which this heat is produced along with the air distribution and the location of the cooling elements.

There are three factors to consider: flock age, flock fertility and storage times. Based on these three factors, there are four general rules of thumb:

  • An egg mass from a "prime" flock with high fertility (between 30 and 44 weeks of age) will produce more heat than an egg mass from a low fertility flock
  • Large eggs (from older flocks) produce more heat than small ones and have a poorer surface/volume ratio with regard to heat dissipation
  • Eggs that have been stored for a longer period of time will produce heat later than eggs that have been stored only shortly, and
  • Eggs from a younger flock will produce heat earlier.

Taking into account these rules of thumb, the following general loading scheme can be drawn:

  • Positions A: highest fertility, oldest (large egg) flock, shortest storage time
  • Positions B: lowest fertility, youngest (small egg) flock, longest storage time
  • Positions C: middle fertility, middle aged flock, middle storage time

Some further guidelines for balanced loading are:

  • Generally, it is not advised to exceed more than 10 weeks of difference in flock age, seven days of difference in storage times and 10 per cent difference in fertility.
  • The setter trolley on which the three OvoScan™ sensors are installed should be loaded with the eggs with medium heat production.
  • Always load the machine symmetrically so that the air resistance is the same on both sides of the pulsator.
  • Never start an incubation cycle when the machine is not fully loaded. If you do, any measures taken regarding balanced loading will be ineffective.

The above guidelines are a good way to get started when loading eggs from different flocks. But ultimately, experience will dictate the optimum flock mix, and only site-specific comparative trials will identify the overall absolute limitations.

July 2013