Professor Nick Sparks - January 2014.
While eggs hatch successfully in the wild without human intervention, the farmer is part of the food chain and should minimise the risk of harmful micro-organisms (pathogens) and spoilage organisms contaminating the egg, the developing embryo, or the hatchling.
- Achieving an acceptable low level of microbial contamination when birds are given access to range requires a consistently high standard of husbandry.
- When handling hatching eggs it is worth remembering that, when a fertile egg emerges from the bird, it normally contains in the region of 60-120,000 cells – the early stages of embryo development. These cells are found on the upper surface of the yolk at the blastoderm (seen as a 1-2mm white spot).
- If the embryo is not to be damaged or killed the egg should be cooled immediately after lay to approximately 15°C and held at this temperature until the egg is incubated.
- Care of the hatching egg has two components:
- Preventing the contamination of the egg with harmful microbes
- Providing the embryo with environments that will not compromise its development during incubation, or kill it during storage.
Preventing the Contamination of the Egg with Harmful Microbes
- Minimise the number of ‘floor eggs’ by ‘training’ birds to use the nest boxes from point-of-lay (e.g. closing off dark areas of the house, placing nest boxes near to, or on, the floor).
- Making sure that the nest boxes are kept clean by for example, frequent re-littering of the nest box, particularly when the ground outside the house is wet or muddy.
- Collecting the eggs on sound, clean trays to minimise the number of cracked eggs.
- Collecting (on dedicated trays) dirty eggs after floor eggs to minimise the risk of cross contamination.
- Sanitising hands before handling nest clean eggs and after handling dirty eggs;
- Grade eggs carefully, rejecting second quality eggs (e.g. eggs with cracked shells, incomplete shells, wrinkled shells, very dirty shells or over or under-sized eggs).
- Wash dirty eggs correctly – water will carry bacteria through the shell so every effort must be made to stop water from passing across the shell.
Providing the embryo with environments that will not compromise its development during incubation, or kill it during storage
- It is critical that wash water is held at the correct temperature (normally approximately 42°C but follow instruction on the sanitising machine).
- Use water that is potable and has an iron level of <2ppm (levels greater than this can encourage the growth of bacteria in the egg if the water penetrates the shell).
- Ensure that an approved sanitiser is used and that it is ‘active’ (e.g. chlorine based sanitisers are prone to being inactivated by organic material).
- Do not wash eggs for longer than the period recommended.
- Do not wash excessively dirty eggs.
- Allow eggs to dry following washing.
If the eggs are to be fumigated follow the safety procedures carefully (obtaining expert advice if required) to ensure that the procedure is safe for the operator and the embryo.
Store Eggs Correctly
- Eggs should be stored at a temperature of ~15°C.
- Eggs should be stored for no longer than 7 days typically, or if stored for longer periods the eggs should be turned through 45° every 24 hours.
- Eggs should be stored in relatively humid conditions (~75% RH): humidity control is a balance between preventing excessive water loss from the egg and preventing the growth of fungi, water condensing onto the shells (so called ’sweating’), deterioration of cardboard containers, etc.
- Eggs to be stored pointed end down.
Producing Grade A hatching eggs from birds kept on range requires commitment and attention to detail. Following the guidelines above will help to ensure that the effort expended is rewarded by the minimum number of eggs rotting during incubation, and a high percentage of top quality chicks hatching.
This Technical Summary is funded by the Scottish Government