The impact of genetics on breeder management - By By Ron Meijerhof, senior technical specialist, Hybro B.V., Boxmeer, The Netherlands - In the world of broiler meat production, rapid developments are being made. The increase in broiler performance for all commercial breeds has been tremendous over recent years, measured not only by improvements in growth per day, but also in terms of feed conversion, carcass yield, breast meat yield, mortality and leg quality, for example.

Trends in breeder performance are not so clearly pronounced and regular, however. Today we find that modern breeders can produce peaks of up to 85 per cent, which is certainly more than we could achieve seven or eight years ago. On the other hand, it has become more difficult to obtain these maximum performances, because the birds require much stricter control without room for errors. This is particularly evident in the management of modern males. The reason for this is simple.

Important improvements

When we look at the cost price of a kg live broiler, even without processing, the cost of producing a day old chick is only about 15 per cent of the total cost price, with 85 per cent the cost of growing that day old chick into a broiler. If we calculate the cost price of a kg of meat, including the processing costs, the cost of the day old chick is less than 10 per cent of the total cost price.

This means that the cost of rearing breeders, including feeding, housing, incubation and chick processing, only adds up to 10-15 per cent of the total cost, and therefore that an improvement in breeder performance has a relatively small influence on the total cost price of the bird.

For this reason, improvements in broiler performance are typically much more important than improvements in breeder performance, which in any case are only acceptable if they have zero or negligible effect on the broiler traits. This is why in the long term most breeder companies try to keep breeder performance equal or constant to slightly positive, instead of delivering enormous improvements in breeder productivity that will consequently have a negative impact on broiler performance.

Although all breeding companies are aware of this - and effective in achieving further improvements in performance - not all companies regard the key points for improvement in the same way. Between companies and breeds, we see differences in performance, based on the importance that the individual companies give to certain aspects of broiler production.

Breeding is a long term business. It takes at least four or five years to see a change in pure lines being reflected in product performance in the field. Therefore it is vitally important to assess the direction in which markets will develop in the future accurately – and to anticipate this early enough within the breeding programme to take full advantage of market trends when they occur.

Multiple crosses

Broilers are the final product of crossing several lines. Consequently at breeder level, the genetic background of males and females can be (and almost always will be) completely different. This means that to some extent it is possible to realise broiler trends in the parent line of choice. For example, growth in a broiler can be realised by crossing a very fast growing male line with a normally growing female line, or vice versa. The selection of lines and their specific characteristics has an enormous impact on the reproduction traits, and on the management strategies that have to be applied to a certain breed.

Let’s assume that broiler growth is obtained by crossing an extreme growing, genetically heavy male with a slow growing, genetically light female. As a result, it can be expected that this breed will easily produce eggs but fertility, especially at a later age in the flock, will be more difficult to obtain. When the reverse option is used, so a heavy female with a light male, fertility will be relatively easy to achieve but getting the optimum number of eggs will be more challenging. Given these scenarios, it is clear that the management strategies and practices for these two resulting breeds will be different.

Selection goals and their influence on breeders

The breeding programme for each individual line in a breeding company is defined by breeding goals. In other words, for every line, a selection programme must be defined that describes on which selection parameters the focus must lie for that specific line. Of course breeding companies do not only select for growth, but also for other broiler traits such as yield, meat quality, feed conversion and mortality, as well as on breeder traits like egg production, shell quality and hatchability, for example. The challenge with selection is that it not only changes the parameters that the birds are selected on, but also parameters that at first sight appear to have little to do with the breeding goals.

A good, example of this is in the relationship between growth and reproduction. It is well known that a strong selection on growth has a negative influence on reproductive performance. This means that relatively more pressure has to be put on selection for reproduction if at the same time more pressure is given to selection for growth, in order to maintain constant or even slightly increased reproduction.

However, selection on yield and feed conversion also has an influence on reproduction. If high yielding, feed-efficient birds are stimulated too early and too much with feed without being able to produce the expected eggs, the birds will process that extra feed in their own body and grow excessive meat very rapidly. This meat influences the production of sexual hormones in the birds, and as a result the birds become over-stimulated. This results in poor production and high mortality, because the birds cannot handle the high stimulation of the reproductive tract.

If we take reproduction and growth as an example, we can question what causes the often discussed negative correlation between these two traits. There are two main reasons, either related to the individual hen or to the performance of the flock.

Individual birds
Egg production by an individual hen is maximal if a follicle (yolk) is produced every 24 hours, turned into a first grade quality egg and laid. This egg per day equates to 100 per cent production. When we do select on growth, it becomes more difficult for a bird to produce each follicle in good time. Often it will take the hen longer than 24 hours, and often a pause day (day without an egg) will be introduced. This is because the hormonal or developmental sequences in the bird will not be as optimal as they should be. It is not so much that the optimal sequence can no longer be achieved, but that the circumstances to get the birds into that condition are becoming much more critical. The same holds for the consistency of that bird: how long can it maintain that high level of follicle production without causing more pause days.

Flocks of birds
Of course a flock of birds is a mix of thousands of individuals, each with their own individual capacity to lay eggs, but also with their own demands on the environment to get into that optimal stage of development for producing an egg every 24 hours.

Due to selection on broiler traits, establishing the correct stage of development and the fine tuning to get to that stage is increasingly critical. The bird is becoming less forgiving in non-optimal situations, and therefore less deviation from that optimal stage is acceptable to obtain good results. As large flocks of birds will show a natural variation in development, the risk of non-optimal treatment for groups of birds increases. Every bird in the group is still able to produce, but as we manage the flock based on the average demand of all the birds, an increasing number of the birds will suffer from non-optimal conditions. Factors that increase that natural variation in development (poor rearing, high stress, poor equipment, high disease pressure etc.) will make it even more difficult to obtain good results.

Consequences for management

Selection for fast growing, high yielding broilers influences the reproductive capacity of the parent stock. To obtain good results in reproduction, we have to focus on delivering adequate management to address the needs of this specific type of bird.

Start of the flock
As individual birds accept less and less deviation from the optimal, it is crucial to have a very uniform flock at the onset of lay, to get as many birds as possible to that point simultaneously. This is more than just uniformity in bodyweight at a certain age, as it also includes uniformity in development. Achieving maximum uniformity is also about more than grading. It starts with good chick quality and start up of chick development, uniformity in frame size and the avoidance of stress and diseases, among other factors. The start up period is especially important.

High-yielding broilers (and therefore their parents) are normally selected to have a high development of organs before the real growth starts, to be able to support the rapid growth of protein later in life. This increased development in the first days normally means that the birds tend to start rather slowly and are more sensitive, especially to temperature. It is therefore very important to ensure that the house is sufficiently preheated before the birds arrive, to prevent them from becoming cold. If the birds become cold shortly after arrival, some of them will not find the feed and water for several days, and uniformity will already be adversely affected after just one week.

Quality of rearing
Even more than with classical breeds, the rearing period of high-yield breeders is crucial for obtaining maximum reproduction results. Focusing on the quality of rearing, uniformity of the flock and adequate development at the start of production pays off very rapidly. The key word in rearing is ‘gradual’. It is important to avoid changing the feed amounts too rapidly, but rather try to gradually increase the feed week by week. In the first 6-7 weeks of rearing, the weekly increase is 2 to 3 grams, then it changes to 3-4 grams until 15-16 weeks of age. In the final weeks of the rearing period, the increases will be 4 to 5 grams each week. It is very important that these weekly increases are steady and constant, to avoid any sudden changes. That sometimes means that even if the flock is a bit over- or under -weight, we should not try to correct it too quickly, but rather try to anticipate development for the coming weeks.

Start of production
A crucial period in the development of high-yielding breeders is the onset of lay. Genetically, these birds are capable of producing high amounts of (breast) meat. Managing the amount of meat growth is very important for obtaining good results. A minimum amount of fleshing is needed, to get the birds ready for egg production. However, over-stimulating with feed in this period to push the birds into egg production has a very negative impact, as the birds will grow meat very rapidly. This rapid meat growth will over-stimulate the sexual hormones and the reproductive system, resulting in poor production and high mortality. This means that the amount of fleshing must be limited by restricting feed stimulation. In this respect, high-yielding breeds in particular differ from more traditional breeds, as they are not able to handle such high feed stimulation.

The best tool for controlling this is to check the formation of the breast muscle on a regular basis. The aim is to have a U shaped breast for optimal production. If a bird is underdeveloped, the breast will feel like a V, which means that there is not a lot of meat around the keel bone. If we over-stimulate the birds either in feed quantity or in protein, we see that the breast muscle quickly develops in a W shape, which indicates over-fleshing. This over-fleshing will result in reduced production, more double yolks and increased mortality. When the birds are well developed, it is important not to over-stimulate them with a high amount of protein. To prevent this, increase the feed amount in a steady line from end of rearing to start of production, aiming at approximately 120 grams of feed at 5 per cent, regardless of the age of the flock.

Peak feed

Genetic selection for growth also influences the choice of management during the peak production phase. A strong selection on growth will mean the birds grow very fast if feed intake is not well-controlled. This means that for fast growing breeds, the amount of feed has to be reduced after peak more rapidly and aggressively, to control growth and maintain persistency and hatchability. Start feed reduction as soon after peak as possible, or the birds will gain weight on the excessive feed that is given - and then require extra feed to maintain that extra body weight.

It is good practice to reduce feed amounts one week after peak production is reached. Reduce the feed for three weeks by approximately 2 to 4 grams a week, divided into two feed reductions per week. After each feed reduction, monitor egg weight, body weight and production. While both egg weight and body weight should continue to increase, production should not decrease by more than one per cent each week. Only if that is achieved, introduce the next feed reduction.

After these three weeks of feed reduction, continue to reduce the feed by one gram per week until about 45-50 weeks. From this point onwards, it is often advisable to maintain constant feed. The aim of this whole feed reduction process is to keep increasing the bodyweight after peak at a level of about 10g per week. This is not because the birds need to grow 10 grams a week, but if the flock grows on average 10 grams, the poorest birds will at least not lose weight.

Conclusions

Changing the characteristics of birds by genetic selection has an influence on the capacity of the birds to reproduce. Not only selection on growth, but also on meat yield and feed conversion has, among others, a negative impact on reproduction. This can be partly recovered by putting more selection pressure on reproductive performance, and partly by adjusting the management programme to the specific birds. Applying classical flock management conditions to fast growing, high yielding breeds will not automatically give the highest production results. Continuous adjustment and fine-tuning of the management programme to deal with the continuous genetic changes in the birds is necessary.

Source: Hybro B.V. - May 2005