In the icy weather that we are currently having, the Accident and Emergency Departments in the hospitals are likely to be treating an increased number of people with broken bones. It is likely that there will be more elderly people with broken bones than young ones. Bones can become more fragile as we get older. We don’t bounce so well! Broken bones are also found in your laying hens especially when they get towards the end of their laying life. It is at this time that the risks of the bones becoming broken are increased, partially because we have to catch the hens. Clearly egg producers are well aware of the risks. However it could be useful to discuss whether it is possible to prevent or minimise breakages during the time when on the laying farm.
In discussing bone breakages in hens, we need to look at the heritability aspects; nutrition; management and also the welfare implications. We can get a lot of clues from what happens to humans, apart from the self imposed detrimental effects on bone strength of alcohol, soft drinks and smoking! Even without having had a Friday night ’booze up’, hens unfortunately have a problem of fragile bones.
Firstly, you will often see the word Osteoporosis in veterinary reports and articles on welfare. What does it mean? The literal translation is ’porous bones’.
Yes, the mineral density of the bones changes with age. They can become less dense and porous, lose their elasticity and become more prone to breakages. For example, in humans aged about 75 or more, females are twice as likely to get osteoporosis than males.
The bone mineral density is reduced but lifestyle changes can help to slow down the degradation. Exercise is of help in reducing the risks of broken bones. In addition, it helps to increase the calcium and vitamin D intake.
Once bones have been formed, they do not then remain in a sort of dormant state. A continuous process of resorbtion and regeneration goes on. The ability for this to happen depends on correct nutrition, coupled with correct hormone levels. These factors are especially important during the rearing phase of the pullets. The absorption of some nutrients from the gut can deteriorate, as our hens get older.
Nutrition
Hens need to lay eggs with a good shell quality. To do this there has to be the correct ratio between calcium and phosphorus in the feed. Both of these minerals are also important in the prevention of osteoporosis.
The long bones in hens have a central cavity that is special to hens. It is called the Medullary Bone. When your pullets arrive at the laying site, the Medullary bone is relatively undeveloped. The calcium content of the hens’ feed is increased as they are coming into lay and the increasing oestrogen in the blood encourages the formation of this storage area for calcium. When the hens have not been able to get enough calcium for tomorrows’ egg, calcium is released from the Medullary bone into the blood stream to top up what is needed for the eggshell that is being formed during the night. When there is too low a calcium intake from the feed, the long bones can become deprived of calcium and may become brittle. Should oystershell be fed therefore? No, because it has a high calcium content but little phosphorus. An imbalance of these minerals could cause damage to the kidneys as they struggle to excrete the excess calcium. In addition, hens can have a depraved appetite for oystershell and this could lead to the crop becoming full of it, rather than of the carefully balanced feed that the compounder has delivered to you. In practice on free range farms, it is very difficult to ensure that all hens have an equal opportunity to ingest oystershell, so I suggest that you leave it to the compounder to get the correct amount of calcium into the hens.
In practice it is advisable to adopt a phase feeding method of supplying the hens nutritional needs. The calcium content is usually increased during the laying period, partially because the hens’ gut becomes less efficient in absorbing it into the blood stream, as they get older. The phosphorus content tends to be reduced, so the ratio between the two becomes wider and shell quality is hopefully maintained by these actions. At the same time, osteoporosis is discouraged by these nutritional manipulations.
Calcium has to be absorbed from the feed and into the blood stream. Some hens are better at that than others so within a flock, there may be hens that are more at risk of broken bones than others. (In practice, only about half of the calcium in the feed ends up in the hens blood stream). There is a conflict in the hens’ nutrition in the early part of the laying period because for the development of the oviduct, a feed with a high amino acid (protein) content is required. This may induce looser faeces that may have an increased calcium loss in the hens, just when they are trying to finalise their bone and Medullary bone formations. In practice there is little that producers can do about this. However it is one of the many stressors with which the hens have to cope.
Vitamin D helps the body to store calcium and about 99% of the calcium in the body is stored in the bones. The feed contains the hens’ entire vitamin D requirement. However, allowing them onto the range area can increase the vitamin D metabolism. So although a deficient intake of this vitamin can be associated with osteoporosis in humans, it is unlikely to be as important in hens that are receiving a carefully formulated feed. The only detrimental effect in hens is where they are poorly feathered. The sunlight when on the range falls onto bare skin. The increased vitamin D that is metabolised in the hens from this can lead to a loss of shell colour.
We know that fluoride is added to our water supplies to increase the strength of teeth in children. I wonder if there is any evidence to show that the incidence of broken bones in hens is reduced in the areas where their water has had fluoride added?
Activity
It has been known for many years that hens in conventional cages, which are therefore relatively inactive, can develop bones that are more brittle than in active hens. During the pullet rearing phase also, highly active pullets may well have stronger bones than inactive ones. Perches in the rearing phase have a dual role therefore, i.e. they may help in increasing bone strength but also they help in making the hens more adventurous for the rest of their lives and more likely to locate the nest boxes. The development of enriched cages is an important improvement in the welfare of hens. This is because the provision of a bit more space, coupled with the installation of perches and a nesting area into the cages, has encouraged greater activity and a better bone strength. Free range and Barn egg production systems allow the hens to be active. In theory this is a good thing because the stronger bones should be less breakable. Likewise, humans who are active, go jogging, go to the gym and climb the stairs instead of using the lift, have stronger bones than ’couch potatoes’. However, there are other factors that offset the advantage of stronger bones in free range systems such as:
a) Sudden frights. The stress of suddenly ending up in a smother, having probably hit something whilst doing so, certainly can increase bone breakages.
b) Hitting equipment. Maybe the risks of wing damage are higher in multi-tiered systems than in more conventional free range systems? In addition, research shows that in free range systems, the keel bone can become cracked by impacts with something hard such as the equipment in the house. Certainly there is a risk when hens are required to fly from one tier down to the next and then down to the floor. Manufacturers are aware of this risk and most try to decrease this risk by innovative designs. For more conventional free range systems, where the hens move from the litter area onto a flat slatted area, the risks of broken wings should be decreased provided that there is a logical layout of the equipment. Access from the litter to the centrally placed nests can be almost risk free, especially where the base of the chain feeder is almost touching the slats. It is surprising therefore that some feel that it is desirable to make this area more cluttered by the introduction of more perches. Surely this will increase the risks of wing or keel bone damage? Many hens have satisfactorily settled down for the night on the slatted area for several years now without showing any signs that they think that this is a welfare insult. Why impose a human aspiration onto contented hens? Why make it much more difficult to inspect the hens to ensure that their welfare is optimal? An increased number of perches may well do that.
c) It is easier to catch hens that are in either conventional or enriched cages than in a free range house. Careful advanced planning is necessary, such as the ability to have very dim or blue lights. Whereas, most caged units have control of the light intensity in the house, in some free range houses, this is not really possible. How to minimise the risks of damaged bones at the depopulation of the house deserves an in depth article in The Ranger.
Heritability
The Breeding Companies have to select for so many traits. Bone strength is one of the important ones and it is one that can effectively be passed on to succeeding generations. They are aware of the need for good bone strength but at the same time they must select for a high level of egg production. Therefore they have to produce a hen with a suitable frame size, which allows the calcium to be withdrawn from the bones for egg production when necessary. It is a highly complicated thing to ensure that the laying hens that are in use on farms have the optimal balance of all of the many traits that have to be incorporated into the selection process.
It is the hens’ genes that determine the potential size and strength of the skeleton. Whether this is achieved or not depends predominantly on the management during the rearing stage. The bone building cells (osteoblasts) are highly active, especially during the middle part of the rearing phase. The quality of the feed and the environment at this time are highly influential on the final result. So the correct genetic make up and good nutrition coupled with an active life in the rearing house play an important part in the quality of the pullets that you receive.
I suspect that in time there will be a gradual decline in the number of hens with bone breakages that are associated with the genetics of the bird.
Welfare
Not surprisingly, free range egg producers care about the welfare of their hens. It is in no ones interest to have a flock that are damaged, whether intentionally (no one with the necessary empathy with hens does that) or unintentionally. A flock that has suffered a welfare insult is unlikely to be profitable. The increased emphasis on training those responsible for the husbandry and those with specialist tasks such as catching and transporting the pullets and hens is obviously a positive step. Any of us who have handled the end of lay hens do not forget the shock of feeling a bone break. It is not something that one forgets and we all do our damnedest to ensure that it happens as infrequently as is possible. Therefore training, an awareness of the risks and care are the key words here. These assets are now reinforced by the legal obligation to safeguard the welfare of the hens. In the old days it was not unusual for hens to be carried by one leg but this practice is now correctly outlawed. A big change for the better has happened since the re-emergence of the free range system of egg production. This is a good thing because, in terms of the risks of poorer welfare because of broken or cracked bones, the increase in the free range egg industry has not been a positive step.
The implication of what I have been saying is that hens and female humans are remarkably similar. Certainly, there are some common factors in the digestive system of humans and hens and the quality of the bones. However, I fall short of saying that our female loved ones are just overgrown hens! I wonder which of the two go broody the most frequently? However, we males do not object to being ’clucked over’!
So "break a leg" – no not literally!!
