Candling is a means of identifying infertile and early dead embryos. Trays of eggs are passed over a strong light source which clearly shows infertile and early dead embryos. Candling is not routinely done in every hatchery, because it requires extra equipment and labour. However we recommend to candle a sample of each flock weekly to monitor the status of the breeders. If candling percentage exceeds 10 %, then all eggs should be candled, the clear eggs removed and hatcher trays refilled to 95–100 %. This will improve the technical results.
Candling is usually done between day 9 and 10 or included in the transfer routine. If done at transfer often an automatic candling machine with egg remover is used to keep pace. These machines are quite expensive and do not pay off for small hatcheries. Used in many hatcheries is a candling table, which illuminates an entire setter tray from beneath. Ideal for candling samples is a spot candler. It is by far the cheapest and most accurate method, but requires some training and is more time consuming when doing big numbers.
If candling is combined with the breakout of clear eggs, it is the best method to identify fertility (see chapter “Breakout analysis” for more details). Eggs set upside down, cracked eggs and other second grade eggs can be also noted at this stage. Such a candling breakout analysis can be an important part of the quality control program of a hatchery.
The setter trays are designed to maximise the amount of eggs that can be set in an incubator and to allow an easy turning of the eggs. However they are not suitable for hatching, because of the simple reason that the chicks would fall down from the trays. Therefore the eggs are removed from the setter after 18–18.5 days, transferred from setter trays to hatcher baskets and put in separate hatcher cabinets. In this way the transfer helps to keep the large quantity of fluff generated during hatching away from the clean areas of the hatchery.
When different batches of eggs are set in one incubator, one should separate them during transfer into different hatchers (if machine capacities allow). This will harmonise the hatching process, reduce the spread of hatch and improve chick quality. However a completely filled hatcher with different batches of eggs is preferred to one only partly filled.
Very important during transfer is to assure a smooth process. The Staff should understand that the growing chick has used calcium from the shell for growth and shells are very fragile at this stage. Do not expect any chick from an egg that got cracked.
The temperature in the transfer room should be at least 25 °C / 77 °F and no trolley should be outside of an incubator for more than 30 minutes. If the transfer is well organised, each trolley (approx. 5000 eggs) can be done in less than ten minutes. This avoids an excessive, uneven cooling of the eggs, which would increase the spread of hatch. Of course transfer should only be done into clean, warm and dry hatcher baskets and hatcher cabinets.
Do the basics right
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