Feather Pecking in Layers
A review of recent research and recommendations.
By Peter Hunton, ISA Consultant and Past President, World’s Poultry Science Association
Feather pecking(FP) has probably been a feature of chicken behaviour since the species first evolved, but has acquired much greater importance as poultry keeping became more intensified, and modern systems of management were introduced.
Research studies on FP date back to the 1970’s, but new approaches became necessary as consumers intensified their concerns with bird welfare in the 21st century. This article is mainly based on two review papers published in the World’s Poultry Science Journal: Rodenburg et al, 2013, WPSJ vol. 69, pp 361-373 and Nicol et al, 2013, WPSJ vol. 69, pp 775-788. The co-authors come from institutions in The Netherlands and the United Kingdom, and the research reviewed was largely conducted in these countries.
It is clear from these reviews that there are two types of FP; gentle and severe. Most studies suggest little relationship between the two types.
Gentle Feather Pecking
Gentle FP may begin as early as one day of age. It consists of exploratory, non- aggressive, pecks at the down or plumage of flock mates. No damage results and the behaviour is considered benign. Because of this, gentle FP will not be further discussed here. Some research has shown separate gene expression for gentle and severe FP.
Severe Feather Pecking
Severe FP consists of forceful pecks and pulls of feathers, and often involves eating of the feathers. Victims become progressively bare of feathers on their backs, tails and vents. Sometimes, severe FP evolves into vent pecking, which can lead to the death of the victim. This is especially important among pullets early in the laying cycle. However, vent pecking may arise independently of FP, so the two behaviours are not always found together.
The number of birds actively participating in FP may vary. Some observations showed relatively few birds involved, but in other cases, close to 100% of the flock. This clearly influences the outcomes in terms of flock damage.
A third form of FP, called aggressive pecking, targets the head and neck, and is largely used by birds to establish social order.
Causes and Risk Factors
It is clear that there is no single cause of severe FP. A large number of factors that appear to affect both the incidence and severity of FP have been documented. These include age, nutrition, genetics, lighting intensity and colour, the overall quality of the rearing process, beak trimming status, stocking density, presence or absence of litter material, litter substrate, hormonal status, management system (conventional cages, furnished cages, aviary, free range), and fearfulness. This list may not be exhaustive, but it comprises most of the factors that have been studied over the past two decades. Those considered to be of greatest practical impact are discussed below.
Depending on many of the risk factors listed, severe FP may begin at any age. In general, it has been found that once FP begins, it is difficult to stop, and the earlier the onset, the greater the chance of progressively greater incidence as the birds grow older. Thus it is most important in practical situations to take all possible steps to prevent or limit the early onset of FP.
Because some birds that pull out feathers from flock mates proceed to eat them, early research investigated whether this might be the result of a nutrient deficiency. Feathers contain a relatively high level of fibre; it has been shown that increasing the level of dietary fibre, particularly insoluble fibre (e.g. non-starch polysaccharides [NSP]) can sometimes reduce the incidence of FP.
Another nutrient that might be deficient is lysine, even in diets formulated to support maximum egg mass output.
Earlier research showed that deficiencies of magnesium, sodium and zinc, could also result in increased FP behaviour, but it is unlikely that contemporary egg laying diets would be so deficient.
High light intensity can provoke FP, particularly when other risk factors are also present. Reducing light intensity has been an accepted management strategy to reduce FP in commercial situations, and its effectiveness has been demonstrated experimentally. However, this method of control, at least if taken to the point at which it is effective, may have other undesirable welfare consequences. These consist of unwanted changes to eye anatomy and function. Some success in limiting FP has been achieved with the use of red light, but this too has some negative welfare implications. Therefore it is important to start with sufficient light intensity and to not reduce intensity if FP does not start.
An interesting recent observation relates to the use of dark brooders. In many conventional brooding systems, chicks are exposed to continuous lighting during the first several days or even weeks of life. This results in active chicks feather pecking inactive (sleeping) ones. Providing a dark, heated area, or a dark period in a fully heated house, has been shown to significantly reduce severe FP and improve feather cover in growing pullets.
While most of the research reviewed dealt with floor managed flocks, we can assume that in principle, caged flocks follow a similar pattern. Floor birds housed at >10/m2 are at greater risk of FP, and this tendency is increased in larger colony sizes. Colony size also affects FP incidence in cages, with the best results from the smallest colonies. This, of course, favours the conventional cage, no longer legal in Europe, but widely used elsewhere. In furnished cages, small colonies also do better, a fact in conflict with the trend towards larger colonies presently in progress. In addition to the two-dimensional floor space, lower rates of FP can be anticipated when birds have access to perches (from 4 weeks of age onwards) litter material from day-old and when chain feeders and bell drinkers are avoided.
Floor managed flocks fare much better with respect to FP where litter is provided, and where foraging is encouraged by placing feed or grit among the litter. In terms of litter material, straw or wood shavings have been shown to be the preferred form. Keeping litter dry and friable is also important in ensuring minimal risk of FP in floor house pullets or layers.
Early studies suggested that FP develops as a substitute for ground pecking when the hens do not have the opportunity to practice this behaviour. This may develop early in life; birds raised on wire floors, even if later transferred to litter management, tend to have more feather pecking and hence poorer feather cover.
It has been almost universally found that the more “freedom” given to pullets and hens, the more susceptible they are to FP. So small conventional cages have the least, and free range the most, risk of FP and the resulting social, welfare and economic consequences. In many countries, management systems are being dictated by the marketplace, and so farmers have little choice other than working to minimize risk factors for FP in the system they have to adopt. Fortunately, the research reviewed in Nicol et al (2013) is helpful in addressing these challenges. For example, a study of non-cage flocks in the UK showed that more than 40 strategies associated with reduced FP damage could be specifically applied to various flocks with positive results. Those most frequently and successfully applied were: ensuring >50% of the birds used the range on sunny days, limiting diet changes during the laying period to 3 or less, having >1 person conduct flock inspections, house temperature >20ºC and ensuring adequate loose litter material throughout the laying cycle.
Interestingly, beak trimming, although industry’s main method for limiting FP, is not always effective, and in one study, researchers found more plumage damage in beak trimmed pullets than in pullets with intact beaks. Both FP and plumage damage have been observed in beak trimmed flocks, although anecdotally, beak trimming seems to be a worthwhile method to reduce FP and plumage damage. This is particularly true when beak trimming is done using the infra-red beak treatment at day-old in the hatchery.
However, the welfare aspect of beak trimming, once thought to be minimized by use of correct procedures and equipment, seems to be again in question. Based on past experience, one may predict that more and more restrictions will be placed on the practice, or in some countries, an outright ban.
The results of severe FP can cost commercial enterprises dearly. Reduced feather cover increases energy requirement and reduces feed efficiency. In addition, if FP progresses to vent pecking and/or cannibalism, very high rates of mortality can be experienced. These can result in serious economic loss. And it can be debated whether the improved welfare from not beak trimming, compensates for the decreased welfare of the high rates of mortality associated with cannibalistic vent pecking.
When all else fails, blame genetics! From the early days of research into FP, it was obvious that genetic differences existed between strains, lines and individual birds with respect to their susceptibility. When the Scandinavian countries moved to non-treated, non-caged egg-production, close to 95% of the total egg-production changed to White Leghorn genetics. In general, brown egg strains show higher incidence of FP than white, and there are well documented differences among hybrids and pure strains in both categories. But difficulties in measurement of individual birds, and a host of other factors, made this an unattractive field for applied geneticists. The classic work of Muir and his associates at Purdue University, originally reported in 1996, showed that the challenge could be met in a practical way. They housed family groups in multiple bird cages under fairly harsh environmental conditions (high density, high light intensity) and selected for egg production and FP related mortality. Within a few generations, lines selected in opposite directions showed major changes, to the extent that the line selected for improved production and reduced mortality could survive and lay well under the harsh conditions, while a contemporary commercial hybrid could not. Additional studies in The Netherlands have repeated these results, and in addition have developed selection methods in which individual hen data can be combined with family (full-sib or half-sib) data into a selection index. Hendrix Genetics and ISA are closely associated with this work.
While feather pecking continues to be a challenge for commercial egg producers, improved knowledge and understanding is available to help farmers limit its effects. Combined with the emergence of improved strains, resulting from modern selection techniques, a variety of strategies exists that can reduce FP to acceptable levels, and avoid serious economic and social consequences.
“At ISA, the breeding program incorporates strategies that genetically improve behaviors (including FP and beak inflicted injuries) which are associated with bird well-being as we develop products to produce more efficiently under a variety of environmental and flock management systems.”
Dr. George Ansah
Institut de Sélection Animale BV - ISA
P.O. Box 114
5830 AC Boxmeer / The Netherlands