Genetics is the key to bone strength

Breed companies hold the key to resolving the growing concerns over bone breakages

in free range and barn laying units.

That’s the conclusion of new research into the issue that is threatening to cast a welfare shadow over the future of non-intensive systems.

The research, at the Roslin Institute in Scotland, also discovered that exercise and the feeding of limestone can strengthen bones. The new findings were revealed at a conference arranged by Defra to review its on-farm poultry welfare research programme.

Two other research projects, both based at Bristol University, threw new light on the extent of a problem now widely regarded as the most severe welfare issue for layers.

It remains unclear how and why the bones break and, ironically, the issue remains invisible to producers because birds affected appear to show no symptoms.

As highlighted in the Ranger in May scientists researching depopulation reported finding old breakages in over 50 per cent of birds. The latest research confirms those levels.

It is assumed that the development of the modern hybrid layer has resulted in bones which do not have the strength to meet the requirements of life in non-cage systems. Whether house design is an important factor is yet to be established. Ironically although the freedom of movement in non-cage systems does lead to stronger bones the activity also leads to more breakages.

The Scottish research team, working with breed company Lohmann Tierzucht, has developed two strains of layer one with high bone strength (H) and one with low (L). Using these birds their latest work involved feeding diets enriched with limestone and measuring the bone strength at the end of lay. They found that the H line had a bone strength as much as 60 per cent higher than the L. Birds able to exercise in an aviary had bones up to 35% stronger than those in cages.

They also discovered that limestone fed in particulate form, rather than powder, also increased bone quality. They concluded “genetic selection can be very effective in improving bone strength”. Allowing birds exercise and feeding limestone can add to breeding improvements.

Of the two Bristol projects one, which examined the effect of stocking density on the welfare of laying hens, has now been completed. It studied six flocks of birds kept in identical aviary systems at stocking rates of 7, 9 and 12 birds per square metre. It found no dramatic differences in bird condition caused by increased stocking rate.

But Prof Christine Nicol who led the research team reported: “The most striking finding in post-mortem analysis at the end of lay was the high prevalence of old fractures in birds from all six flocks.” Prof Nicol has suggested further research to establish the causes and timing of the breaks.

The second, on going, project is looking specifically at breakages. The team told the London conference: “Bone breakage in laying hens is a major welfare and economic problem for the poultry industry and recent evidence obtained from flocks housed in single tier aviaries suggests that the levels of damage being incurred are increasing.”

The research team is checking for the presence of old breaks in end-of-lay hens by monitoring birds at a commercial processing plant. One hundred birds from up to ten flocks will be monitored covering five types of housing system including enriched cages, aviaries and free range (mobile as well as static).

They will search for breaks in limbs and keel bones through the flesh of the birds and will check their findings by dissecting a sample of those tested. Bones will be tested for condition and breaking strength. The findings will be related to flock management and housing design.

They will use the same system to assess birds at 25, 50 and 72 weeks in six aviary and six free range flocks. At the same time bird activity will be recorded on video cameras. At the half way stage they have confirmed that breakages are “high” and that they did not occur during the rearing phase.

Will perches cause more breakages?

Could the use of perches cause more bone breakages in laying flocks? The question has been raised against the backdrop of growing concern over bone damage and the fear that the EU could insist on a full 15 cm of aerial perch for every hen.

Mark Williams, chief executive of the British Egg Industry Council, has written to Defra asking for flocks using perches to be included in the on-going research into the issue.

This could be achieved by looking at units in Scotland where SEERAD already insists that all flocks have aerial perches.

Mr Williams says in his letter that he is concerned that the high levels of bone breakages found by research could be worsened by aerial perching and that the industry could be forced into meeting requirements that could result in poorer bird welfare.