Chestbone abnormalities in laying hens are caused by a combination of factors. These abnormalities may take the form of deformities and/or fractures.

A deformation is defined as a distortion of the bone; the sternums of affected hens are bent sideways or indented at the front. Occasionally, a hen’s sternum is deformed in both directions.

When it comes to bone fractures, a distinction is made between traumatic and non-traumatic fractures. Unlike traumatic fractures, non-traumatic fractures are not caused by an external force (e.g. impact with a hard edge). In these fractures, the broken ends of the bone are often very close together and the periosteum remains intact. On X-rays, they appear as fine hairline cracks. These fractures usually occur in older hens as a result of bone fatigue or osteoporosis. In the case of traumatic fractures, the severity depends on the force involved. The more severe the collision within the housing system or the greater the force, the greater the extent of damage to the bone. The spectrum ranges from small broken bone ends to severe comminuted or splinter fractures. Over the course of the rearing period, a laying hen’s sternum may fracture several times. Both types of fracture described can occur in the same bird.

As very few poultry houses have X-ray machines that would be ideal for detecting bone fractures, the method of palpation is used instead. In this process, the examiner feels the breastbone of individual hens and detects any deviations from the ‘normal’ breastbone shape.

The changes identified in this way are assessed and recorded using an objective scale. Corresponding assessment scores can be found, for example, in the M-Tool. In a flock, at least 50 hens, selected from all areas of the house, should be palpated. Based on the affected animals within this sample, the proportion of likely affected animals in the entire flock can be estimated.

The examination can be carried out without significant additional effort during regular weighing and/or plumage assessment. This provides a comprehensive overview of the flock’s condition. With a little practice, the examiner can quickly and accurately assess the breastbone health of the hens.

As breastbone health is highly likely to deteriorate with age, it is advisable to carry out the assessment regularly throughout the laying period. The following times are particularly suitable for this:

- immediately after the hens are moved into the laying house

- when laying begins

- at peak laying

- at 45 weeks of age

- shortly before culling

The development of sternum changes within the flock makes it possible to identify critical times or phases during the rearing period. It can provide clues as to possible causes and, consequently, suggest appropriate preventive measures.

Ideally, the housing systems in rearing and laying houses should be very similar, so that the hens find it easier to find their bearings and move around the system after being moved to the laying house. In the rearing house, certain systems have proven effective in supporting the mobility of pullets: adjustable systems and the early provision of climbing aids promote the animals’ musculoskeletal and coordination development. As a result, they move more confidently and skilfully in laying houses with aviaries. Information from the rearing farm regarding housing and management during the rearing period is also important in order to minimise the stress associated with the move to the laying house by ensuring conditions are as similar as possible.

Different genetic backgrounds exhibit differences in physique and behaviour. For example, white laying lines are on average slightly lighter than brown ones and make greater use of higher levels. If white and brown laying hens are kept together, stressful situations may arise due to the differing characteristics and requirements of the respective laying lines. In the worst-case scenario, the flock becomes restless, the risk of accidents increases, and consequently the proportion of hens with breastbone injuries rises.

It therefore generally makes sense to house only birds of a uniform genetic origin, reared in the same rearing house, as a flock. This also simplifies the provision of performance-appropriate care for the hens in line with the requirements of the respective laying line.

Laying hens have high nutritional requirements. An adequate supply of calcium is particularly important for breastbone health, especially during periods of sustained high laying performance. Ideally, calcium should be provided in the form of coarse and fine particles in a ratio of 70% to 30%. In addition to a performance-appropriate proportion of calcium in the complete feed, it is advisable to provide supplementary feed lime, particularly in the afternoon and evening, as the hens’ requirement is then at its highest due to eggshell formation during the night.

The exact composition of the feed should be adjusted to the birds’ performance throughout the laying period (phase feeding). Those with the option to control multiple feed silos can vary the ration composition according to the time of day to further optimise the hens’ nutrient supply (split feeding). The provision of acid-resistant stones (‘gizzard stones’) to aid feed grinding in the gizzard, as well as unrestricted access to clean drinking water, should be standard practice. A feed scale is recommended for every laying hen house to record the daily feed intake per hen.

In addition to feed management, other measures have proven effective in preventing brooding leg damage: in the first few days after housing, the birds should be moved from the scratching area into the system in the evening, or areas beneath the aviary should be temporarily blocked off to ensure that all hens consume feed and water. Delaying the switching off of light sources (dimming) signals the end of the light period to the birds. This dimming phase should last at least 30 minutes to allow the birds to ‘calmly’ seek out their roosting places in the upper areas of the aviary with a low risk of injury.

At the time of transfer to the laying house, usually at 17 or 18 weeks of age, the hens are not yet fully grown and the skeleton, including the sternum, is not yet fully ossified. If the hens are stimulated to lay eggs at an early stage, this can have a negative effect on skeletal development and, consequently, lead to changes in the sternum. The start of laying should therefore not be forced before the end of the 21st week of life.

The hens’ general state of health may also be linked to sternum damage. Regular health monitoring must therefore not be neglected. This includes, amongst other things, checks for ectoparasite (mites) and/or endoparasite (worms) infestations, including their control, as well as the early detection of feather pecking. In addition to safeguarding animal health, which contributes to stable performance, regular checks also help the flock become accustomed to human contact. As a result, the birds perceive the presence of humans less as a threat and behave in a more relaxed manner, which also helps to reduce the risk of accidents within a flock.

Despite all preventive measures, it is unlikely that changes to the breastbone can be entirely prevented. However, livestock farmers have a wide range of options and levers at their disposal to promote breastbone health in hens and thus make an important contribution to animal welfare.