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Holostic Approach Needed to Prevent Osteoporosis and Bone Fractures in Laying Hens

by 5m Editor
23 February 2011, at 12:00am

The Farm Animal Welfare Council has reported on its review on osteoporosis and bone fractures in laying hens, which are judged to be serious welfare issues in terms of pain and limiting the bird's mobility to reach feed and water. Breeders, nutritionists, housing/equipment designers, farm managers and legislators need to work together to eliminate these conditions, it concludes.


The aim of its Opinion on Osteoporosis and Bone Fractures in Laying Hens is to review the implications of osteoporosis and bone fractures for the welfare of laying hens, particularly in light of the forthcoming ban on conventional cages in Great Britain, says the Farm Animal Welfare Council (FAWC). The report was published in December 2010. Its main recommendation was that the egg industry (including retailers) should aim to eliminate bone fractures in live birds altogether, using a combination of genetics, house design and nutrition.

Extent and Nature of the Topic

Skeletal health is an important aspect of the welfare of laying hens, FAWC point out. Fractures are common but are mostly detected, if at all, after slaughter. They are referred to as either 'old' fractures, i.e. those which occurred during the laying period, or 'new' fractures, i.e. those which occurred during depopulation, transport or slaughter. Factors that influence the incidence of fractures are the weakness of bones, the design of housing systems and handling at depopulation.

Bone weakness in laying hens mainly results from osteoporosis, which is a pathological condition associated with progressive loss of structural bone throughout lay. This makes the bones fragile, susceptible to fracture and in severe cases, it can lead to collapse of spinal bone and paralysis.

The keel bone (or sternum) is initially made of cartilage but ossifies at about 35 weeks of age, explains FAWC. Before ossification, it may become twisted or otherwise deformed. It may be damaged or broken by collision, for example when the hen jumps onto a perch and lands awkwardly. Loss of bone from the skeleton is increased by mobilisation of calcium for egg shell formation and is decreased by load-bearing and biomechanical forces. The hen therefore benefits from walking, hopping, wing flapping and other exercise.

The incidence of weakened bones and fractures is affected by genetics and strain, nutrition, housing system and methods of depopulation and is exacerbated by the high egg output and persistency of lay of modern hybrid strains.

Finally, FAWC adds that hens are subjected to pain as a result of bone fractures.

Welfare Aspects


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There is evidence the prevalence of bone fractures in laying hens is not declining and may actually be rising."

Osteoporosis and bone fractures were recognised as welfare concerns soon after cages were introduced over 50 years ago, but it was some time before it was established that osteoporosis was related to the restriction of movement and lack of exercise. Osteoporosis is further exacerbated by the great egg output of modern hybrids.

Sexual maturation in the pullet is associated with the development of medullary bone and the cessation of re-modelling of structural (i.e. cortical and cancellous) bone. Medullary bone is a calcium store for egg shell formation – each bird requires about 2.3 g calcium each day for egg production –– and is formed at the expense of structural bone. The hen cannot re-model cortical structural bone during lay, which therefore leads to a low density of structural bone, osteoporosis and a propensity to fracture.

Bone fracture is acutely and chronically painful in humans, says FAWC, and the same will hold true for chickens. The effects are worse and healing takes longer if the fracture site is mobile during repair, and a hen must move to reach food, water and a nest box.

According to FAWC, the incidence of bone fractures is greatly increased by trauma, caused by collisions with ‘furniture’ in buildings or by poor handling, particularly at depopulation.

In terms of eliminating or minimising suffering arising from osteoporosis and bone fracture, the design of husbandry systems affects both whether birds perform sufficient activity for adequate bone strength and the risk of traumatic injuries. Genetics and nutrition can also reduce the extent and impact of osteoporosis. Until these improvements can be realised, the decisions of managers and workers determining husbandry and handling practices, especially at depopulation, are particularly important to reduce the frequency of bone fractures.

Extent of Problem

About 30 million laying hens per year are kept in the UK in a variety of husbandry systems, according to FAWC. In terms of egg output, the most common system in 2009 was the conventional cage (46 per cent), followed by free-range (37 per cent) and enriched cages (nine per cent) with barn and organic free range systems accounting for about four per cent each.

It is estimated that about 30 per cent of the total mortality of hens in cages (around four per cent) is linked to osteoporosis, but that the proportion is much lower in hens in non-cage systems, which have a higher total mortality of about eight per cent. Thus the number of hens whose death is linked to osteoporosis is about one quarter of a million per year in the UK. This estimate excludes mortality during depopulation and transport to the slaughterhouse.

The extent of mortality alone indicates significantly poor welfare for many laying hens. There are no reliable estimates of the morbidity due to osteoporosis and/or bone fractures for the industry as a whole.


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"The incidence of bone fractures of laying hens, both during and at the end of lay, is too high in all systems of husbandry."

Legal Context

The following existing regulations were considered pertinent to the report: The Animal Welfare Act 2006 (and the Animal Health and Welfare (Scotland) Act 2006); The Welfare of Farmed Animals (England) Regulations 2007 (and similar regulations in Scotland and Wales); and The Welfare of Animals (Transport) (England) Order 2006 (and similar regulations in Scotland and Wales).

As from 1 January 2012, laying hens may not be kept in conventional cages in the European Union, and thereafter only enriched cages or non-cage systems will be permitted. There are also detailed EU requirements for marketing poultry meat. Commission Regulation (EC) No. 543/2008 requires that meat from birds in which the tip of the sternum is rigid (ossified) must be marketed as from a cock, hen, casserole or boiling fowl. This includes end-of-lay hens.

Critical Issues

FAWC highlighted that there is evidence the prevalence of bone fractures in laying hens is not declining and may actually be rising. More needs to be done to reduce this significant cause of poor welfare, it says. This need is acute in view of the forthcoming ban on conventional cages, which will reduce some causes of bone fracture (particularly osteoporosis) but increase others (particularly collisions in some housing designs).

Selection for high egg production, combined with rearing methods including control of light periods, has produced hens that are vulnerable to bone fractures. FAWC questions whether it is possible to maintain egg output of around 300 eggs in the laying cycle while attaining bone strength sufficient to reduce this vulnerability.

Conclusions

A direct result of selection and management of laying hens for egg production and intensive rearing is a steady fall in the real price of eggs, but laying hens suffer because of bone fractures, according to FAWC.

The incidence of bone fractures of laying hens, both during and at the end of lay, is too high in all systems of husbandry, says the Council. Breeding selection and production system management can reduce this problem considerably and perhaps eliminate it, which is the ideal.

The design and management of systems of egg production needs to be regulated to minimise the risk of bone fractures, both in terms of improved design and hen handling at depopulation. Although raised perches in non-cage systems sometimes increase the prevalence of fractures, particularly of the keel bone, there are other benefits for welfare, says FAWC, so their design and layout of perches needs to be improved to prevent bone fracture.

Regarding nutrition, FAWC says that is difficult to feed calcium in large particles to laying hens and so new methods are needed to benefit bone strength.

While it is not feasible at present to identify all hens on farm with fractures, FAWC says that if hens with fractured bones are detected, they should be treated or culled. The Council concludes that practical techniques and criteria for intervention for use on farm should be developed for public or private surveillance (and should be adopted by assurance schemes among others). Detection of bone fractures at the abattoir is feasible, using palpation for some breaks and automatic methods for others, and could be used to quantify the extent of the problem in particular flocks and to identify and reduce the causes. It would also allow carcasses with newly broken bones to be identified, reducing the number of bone fragments and increasing the value of the meat.

Looking to the future, the modification of restrictions on describing meat from end-of-lay hens as chicken would increase its value and encourage better care of end-of-lay hens prior to and during killing, says FAWC. Killing end-of-lay hens in their housing would avoid the problems of bone fractures during depopulation.

Finally, FAWC concludes that the economics of implementing all the measures to reduce or prevent fractures – breeding, feeding and handling – will need careful evaluation but should not be sole factor in determining outcomes.

Further Reading

- You can view the full report from the FAWC, including the evidence it reviewed and its recommendations, by clicking here.


February 2011