When chicks can't stand the heat

By Ron Meijerhof, Senior Technical Specialist, Hybro B.V. - Modern, fast growing, high yield broiler lines produce a lot of heat during incubation.
calendar icon 8 January 2007
clock icon 5 minute read

If we measure the embryo (egg shell) temperature at the end of incubation with an infra-red ear thermometer, we often observe values of 103-104°F, when we are actually looking for 100-100.5°F as optimum.

The typical effects of these high embryo temperatures are easily observed at hatch and during take off, including:

Increased levels of dead in shells, late deaths

High temperatures at the end of incubation are a risk to the survival of the embryo, resulting in an increase in the number of late deads and embryos that are too weak to hatch. When late mortality (> 15 days) is over 3-4 per cent, high embryo temperature is often the cause.

Weak chicks, difficulty standing

Chicks that do survive high temperatures are weak because they almost died. Especially during take off, when the chicks are transported - eg. on a moving belt, weak chicks sit or even lie down, and when tipped over onto their side or back, will take a long time to get up again. This is bad sign, as good quality chicks tend to stand and try to balance on the moving floor.

Small, pale, underdeveloped chicks

At high temperature, embryos utilise less yolk for development and stay smaller. As the pigment for the feathers is stored in the yolk, this means that the feathers stay more pale.

Poor yolk uptake, unhealed navels

Reduced yolk utilisation leaves a bigger yolk in the chick. This means that the small, less developed embryo has to close the navel over a large yolk residue, causing more navel problems. Overly high temperatures cause black navels (button navels), while too low a temperature is usually associated with string navels.

Blood in and on the shells, navel/yolk sac mortality

Due to difficulties in closing the navel properly, the chick’s navel is still unhealed on hatching. This bleeding navel shows as blood in and on the shells, and allows bacteria to penetrate the body cavity after hatching, causing navel/yolk sac mortality.

Full bellies, hard yolk sacs

Large yolk residues can be measured by opening the chick, or by gently squeezing the chick’s belly. A plump, full belly indicates a large yolk residue and is associated with high embryo temperatures at the end of incubation.

Malposition “head over wing”, skew heads, cross beaks

The normal position of an embryo in the shell just before hatch is with its head under the right wing. In this position, the head is protected from the shell by the wing and the bird uses the wing to move through the shell. At high temperatures, the embryo’s head remains on the wing and a high number with this malposition will be observed when breaking out.

When the head is not protected by the wing, its right side is pushed against the shell. As the hatchling’s bones are very soft, the skull will form in the shape of the shell and the head will be skew, with its left side rounder then the right. This can be observed during a break out, but also just after hatch, as not all chicks in this malposition will be unable to hatch.

When the pressure is too severe, the upper beak will also be pushed away by the shell, resulting in a cross beak.

The embryo uses its wing to move through the shell, in order to pip it open. When the head is blocking the wing, the chick can’t move and is stuck in one position. As it is then unable to open the shell properly, it has to pip a hole and force the shell to break from that single hole. This results in an increased number of pips, and not every chick will make it.

Red spots on beak, dirty nostrils, red hocks

If the embryo can’t move easily, it breaks the shell by forcing it with its beak. This will irritate the beak, creating a little red spot on the top, just there where the comb starts. The nostrils will also become dirty due to the difficult hatching process. As the chick uses it legs to free itself from the shell, and because the weakened, overheated chick will sit down more, the hocks will be irritated and red.

Recognising these symptoms as indicative of overly high embryo temperature at the end of incubation is a very good start to solving the problem.

December 2006

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