Richard Jackson MRCVS
Just as interest in keeping backyard chickens has risen dramatically over the past few years so too has the number of owners buying their own incubators. Chicken Vet often gets contacted by poultry breeders who are concerned about poor hatchability.
Poultry keepers are start to plan their breeding programs for the year ahead well in advance. Whilst looking forward to the breeding season, it is also important to look back at the previous year’s hatchability, as many problems can be tackled before breeding birds are penned up for breeding.
Before discussing fertility issues it is necessary to decide if there is a problem or not. Unfortunately putting a figure on hatchability isn’t straightforward as hatchability will naturally vary between breeds (with heavier breeds in general having lower hatching rates) and it will also vary depending on how closely related the parent birds are (inbreeding is a particular problem in very rare breeds). Breeder age and health are also important factors. Ideally owners should be getting a hatching rate of at least 80%. However it is not unusual for breeders to have hatching rates of around 50% or less.
The first thing to do with poor hatchability is to keep good records. Records should include the hatchability from each breeder pen, the length of time the eggs were stored between being laid and incubated, the results of candling (if done), the numbers of chicks dying in the first week and information regarding whether or not the chicks are hatching early or late. Equally it is important that un-hatched eggs are opened to determine whether the eggs were infertile or if the embryo/chick died during incubation. This can be a smelly and unpleasant job and certainly should be done either outside or in a fume cupboard. It is important where possible to have an approximate idea of how far along in the incubation process a dead chick got before dying (see below).
The first step in ensuring good hatchability is to start with the parent birds. When selecting, owners usually go by the breed standards to determine which birds actually meet them. However it is equally important that owners take into account the general health of the birds when making their selection. Breeder birds with suboptimal health are likely to have poorer fertility and in certain cases, such as with Mycoplasma, pass the disease onto the chicks vertically. When selecting breeding stock always exclude obese birds as obese cockerels will find it difficult to mate with a hen successfully and overweight hens are more likely to become egg bound and may also prolapse.
Once breeding stock are selected, it is important to feed them a breeder diet to ensure the hatching eggs contain good levels of nutrients for the developing embryo. Always check and trim a cockerel’s spurs where necessary.
If owners have a large number of infertile eggs with no signs of embryonic development then it is likely that the cockerel is at fault and the problem is likely to be restricted to one pen of birds. The usual underlying issue is with the cockerel’s ability to mate with the hen. This can be due to the rooster being:
- Lame; as lame roosters will find mounting a hen mate painful and therefore they should be treated for the lameness and not expected to mate until they have fully recovered.
- Overweight; which again makes mating more challenging especially in heavy breeds such as Orpingtons. If owners breed heavy breeds it is important to give them plenty of space to exercise and avoid over feeding them. Remember we want them fit not fat.
- From a short legged breed such as Indian game, which have been selected to have short legs making it difficult to mate successfully. This issue is difficult to resolve. Some breeders have resorted to artificial insemination.
- Bored with the hens. Yes, if the same rooster is kept with the same group of hens he is expected to breed with then he can become bored and reduce the frequency of mating. Ideally the cockerels shouldn’t be kept with the hens he’s expected to breed with until the mating season and ideally the cockerels should be rotated between groups of hens during this time every few weeks if possible. Try not to put a rooster with too many hens (no more than 10).
Another potential source of infertile eggs is due to poor nutrition. Dietary imbalances can cause embryo death and infertility. Always ensure that breeding stock are fed a breeder diet which most feed mills can supply.
If owners are faced with infertile eggs and there is no obvious underlying cause, resting the cockerel for 3 weeks may help then put him back in with the hens and to him again. If there is no improvement in the situation replacing the rooster will be the only option.
The next common cause of poor hatching rates is chicks which fail to hatch. The most obvious sources are incubation conditions and hygiene.
The egg is protected by a waxy cuticle and a shell to keep bacteria out. Wiping or washing the eggs removes this cuticle therefore removing the barrier and therefore lets the bacteria in, subsequently killing the chick or infecting it. Similarly eggs with cracks or damaged shells let in bacteria quicker allowing for infection and embryonic death. We recommend that only clean undamaged eggs are selected for incubation and that they are neither wiped nor washed. If an egg is dirty enough to need washing then it is too dirty to incubate!
Hygiene in the incubator is paramount. Whilst most incubators are cleaned thoroughly some people find it near impossible to clean the fans which can harbour dust and bacteria. It is therefore useful to use an air compressor or hairdryer to blast the dust out of the fan. It may also be worth telling owners to contact their incubator manufacturer about the safest method for cleaning their particular incubator. Ideally though, eggs should be hatched in a hatcher only and not an incubator as hatchers are much more easily cleaned. Always use an approved disinfectant such as Interkokask.
Furthermore if owners have poor hygiene then they can expect to find a number of day olds dying in the 1st week of life due to yolk sac infection.
The environment in which the eggs are kept is an important consideration. During storage eggs should be kept at 75% humidity. The temperature should vary with eggs age. In the first week the temperature should be 20°C, the second week 15°C and the third week at 12°C. After three weeks in storage hatching eggs should be discarded.
The eggs should be incubated at 60% humidity and 38.4°C in still air incubators and 37.5 – 37.8°C in forced air incubators. The hatcher should be 36.9- 37.5°C and 60% humidity. These figures are official guides, however it is worth getting owners to consult their incubator manual as each brand and model will have slightly different optimal settings. If an incubator is set too hot then owners will often have a number of chicks hatching a day earlier than expected. A colder than normal incubator temperature can increase incubation time. Incorrect humidity can result in an increase in the number of dead in the shell chicks. Ensure owners monitor both the temperature and the humidity daily throughout incubation.
Candling of eggs from 5 days and removing non-viable eggs at the earliest opportunity to prevent the spread of disease will also assist in keeping hatch rates up.