Chicken reproduction, Egg Handling, Incubation and Hatching

Chicken Reproduction

Chickens have a relatively long reproductive cycle compared with other animals used for research, like mice, with female chicks taking up to 8 months from hatch to reach sexual maturity and 5 months for male birds.

From about 4 to 5 months of age, young cockerels (roosters) reach sexual maturity, producing sperm and showing secondary sexual behaviours like courting and crowing. Cockerels can remain fertile for several years on average 5-6 years, though the quantity and quality of sperm does decline as they age.

Young female chickens of modern layer breeds, such as commercial strains of Leghorns, reach sexual maturity at around 4 to 6 months of age, and begin laying eggs. Hens will reach peak egg production at around 6 to 8 months old, and most hens will have good egg production for about two years. During that time the most productive layer breeds can produce up to 300 eggs per year. However, age of sexual maturity and egg production does vary between breeds of chickens, and egg production will decline with age.

Importantly, a small number of birds can produce a large number of offspring over a short period. For example, a pen with two cockerels and five hens can produce over 1000 eggs per year.

Fertility assessments information at NARF can be added here.

Egg Handling, incubation and hatching

Egg handling

At the NARF eggs are collected on a daily basis. Once collected they are first washed (with what again), and then stored in a X at a temperature of 12 – 18°C (humidity?). All eggs are individually checked to identify any cracks or damage, before they are stored.

Eggs can be stored for up to 10 days within a temperature of 12 – 18°C, which prevents the embryo from developing. If the eggs are stored for longer than this, their fertility and the probability of them hatching begins to decline. Therefore, at the NARF we tend to not store eggs prior to incubation for longer than x days.

If you intend to store eggs you received from us before use, please notify the NARF so that this can be taken into account.

If a large number of fertile eggs are required for experimental purposes, eggs can be collected and stored, so that they can be set (begin incubation) at the same time. This ensures that the eggs hatch simultaneously, or if chick embryos are to be used, have the same stage of embryonic development. Alternatively, eggs can be set at different time points, to provide embryos at different stages of development.

This ability to store eggs after they are laid, allows for a smaller number of animals to be maintained to provide large cohorts of fertile eggs or chicks for experiments. The maximum number of fertile eggs or chicks that can be provided is dependent upon the size of the breeding flock and demand. Due to this can take x time to bring up new chicks to create addition breeding pens.

Incubation

Fertile chicken eggs will hatch at the end of the incubation period, which is about 21 days. Development of the chick starts only when incubation begins, so all chicks hatch within a day or two of each other, despite being laid over a longer period.

Prior to incubation, the eggs are allowed to get to room temperature (19 – 20°C), as rapid changes in temperature can be detrimental to eggs.

Eggs are placed into the incubator (what model?) with the pointed end down, as this allows the embryo to develop into the air cell. The incubation temperature is 37.5°C +/- and eggs are automatically turned every hour (?).

Eggs are ‘candled’ at day 10 of incubation, to check that development has occurred. This allows for infertile eggs or eggs with arrested development to be removed, saving resources as well as reducing risk of infection to other eggs.

Egg storage and incubation equipment is disinfected between batches of eggs to avoid cross contamination.

Hatching

Prior to hatch on day x, eggs are moved into labelled boxes, why? Cohorts of chicks that hatch simultaneously are weighed and individually tagged. Chicks are then screened to identify their sex, and in the case of genetically altered chicks, to identify whether the transgene(s) or edited gene(s) are present.

To avoid invasive procedures like blood sampling, samples for screening can be taken from the chorioallantoic membrane (CAM), which is a highly vascularised extra-embryonic membrane. For some of the fluorescent reporter lines maintained at the NARF, the CAM or embryonic stages can be assessed with flashlights that emit light in a bandwidth that allows us to visually identify the presence of the fluorescent transgene. This cannot be done with chicks, particularly flashlights that emit light within the UV range, as birds can see a broader range of the light spectrum than humans, including the UV spectrum. Therefore, this could like alter the visual environment of the birds, causing the distress.