hen selection

As more and more is asked of the modern broiler, so genetics companies have to keep an even closer eye on health and welfare, as Frank Siewerdt, Cobb director of genetics explains.

Breeding programmes continue to achieve annual gains in broiler growth, feed conversion and breast meat yield.

But this has been combined with steady improvements in bird health and welfare traits too, such as better leg strength and reduced mortality.

Despite this, some groups still believe the modern broiler has locomotion problems, even though this is not corroborated by feedback from company veterinarians and industry welfare officials.

See also: Recent articles on bird welfare

This is because it is in the best interest of breeding companies to provide birds that thrive and stay healthy. Birds with good legs and excellent cardiovascular function are more efficient in the field and have lower mortality rates.

Geneticists making selection decisions actively pursue those birds that are genetically superior for key traits that influence their welfare. They recognised that there is strong synergy between welfare and bird performance; successful farmers meet or exceed their production goals when the welfare needs of their flocks are met.

Breeding for health

Nature provides great variability among individuals of the same species. Within the same flock, there will be birds that differ in growth rate, meat yield, leg health and general immuno-competence.

The aim is to select elite birds with superior health indicators and the ability to excel in the commercially important traits. A typical elite breeder will have superior leg strength and a fully functional cardiovascular system, and will still be in the top percentiles for the key production traits.

Since at time of selection none of these candidates will have reached sexual maturity, the decisions regarding reproductive ability are made based on information from close ancestors. Leg health is an essential component of reproductive performance, since both males and females need to be able to stand properly for matings to be successful.

All birds reaching market weight are thoroughly evaluated for structural leg defects. Family information is used to remove families that are more prone to traits such as tibial dyschondroplasia and femoral head necrosis.

The result of multiple generations of selection is that birds with the best genes are kept as pedigree breeders, so the frequency of these favourable genes increases in subsequent flocks. This simple mechanism can be quantified very precisely by population genetics theory and it enables the geneticist to improve flocks at a steady incremental rate year over year.

In the field

In addition to the welfare focus in the genetics program, Cobb is improving management techniques that will result in superior health and field performance. Combined improvements in genetics and husbandry have led to improved mobility, health and liveability of chickens at both broiler age and breeder age.

Defects, such as leg abnormalities, will continue to appear on birds because of natural variation and because growing conditions keep changing with time.

But the percentage of birds with health problems is much lower than in previous years.

New diet formulations, adjustments in environmental conditions and market preferences for different processing weights will continue to provide new challenges for geneticists, but the emphasis is to keep improving bird health and welfare.


How to select for leg strength

• Removal of birds with defects at selection: Natural variability will cause birds to have differing degrees of leg strength. When birds reach market weight, each one is physically examined by a trained selector and receives scores for several leg defects. Those with any leg defects are removed from consideration to become breeders.

•  Statistical analysis of data from selection: After several flocks are selected, the data is consolidated into a larger file and summarised. At this point, the geneticist can find out, for example, which families of chickens had the best or worst leg health quality.

•  Removal of breeder candidates based on family information: At the moment when the geneticist decides on which birds will be kept for breeding purposes, he or she refers to the summarised family information and will “penalise” certain birds for belonging to families that had higher incidence of welfare-related defects. At this moment, even some birds that are perfectly normal will not be kept as breeders, even if they exhibit superior growth, feed conversion or carcase yield credentials, as leg defects may “run in the family”.

•  Final examination of chosen breeders before housing: Before moving into production houses, all males and females undergo a final visual examination to verify that they are healthy and physically apt for mating.