- Fleshing – a side effect of selection for broiler characteristics
In breeding programs for poultry meat production, much effort is put on selection for broiler characteristics, as these traits are the money makers in integrated poultry companies. These breeding programs has successfully resulted in fast growing, highly feed efficient and high yielding broilers.
But as breeders are genetically (partly) identical to broilers, we have to consider the effects on breeder performance as well, and some of these positive selection traits for broilers have a less favorable influence on breeder characteristics. To avoid negative effects of these breeder characteristics, the flock management has to be adapted to obtain optimum breeder results. Probably the most critical factor to control in high yielding broiler breeders (both parentstock and grandparent stock) is the amount of fleshing in the female birds at onset of lay.
· Fleshing and hormonal changes
Although not all commercially available broiler breeds are equal, all of them tend to have a female line with substantial genetic capacity for breast meat yield, both in parents and grand parent lines. However, some commercial lines focus more in broiler traits through the female line than others, and especially these ones need to be controlled in fleshing.
In breeder birds the growth of breast meat is positively correlated with the stimulation of sexual hormones. This means that excessive growth of breast meat in female breeder birds result in excessive production of sexual hormones. These hormones control the development of follicles on the ovary, and with an over production of these hormones we get an over production of follicles.
· Over-feeding leads to over-stimulation
Follicles need to grow for 5 to 7 days on the ovary before they are ready to become an egg. If the bird is producing an egg every day, we should see 5 to 7 follicles in different stages of development on her ovary.
If we over stimulate high yielding breeders with feed, either in quality or quantity, we see much more follicles developing at the same moment. As the reproductive system of the bird can’t handle all these follicles, this will lead to a reduced egg production.
Some of these follicles will fall into the body cavity, resulting in an increased level of egg peritonitis and increased mortality.
· Fleshing or over-fleshing
A good indicator for the level of stimulation is the level of fleshing or amount of breast meat. At start of production there must be a certain minimum amount of fleshing on the bird, but we have to control the amount to a certain maximum. We can describe the level of fleshing with three different shapes, represented by three different letters, as shown on the drawing.
- If the fleshing represents the letter V, it means there is only a very limited amount of breast meat present on the bird, and the sharp shape of the keel bone can be felt easily. The situation like this can sometimes happen to more classicial types of breeders, but will be rarely found in modern high yielding lines, excepting some individual, extreme birds. This amount of flesh is not sufficient for optimum production
- If the fleshing represents the letter U, the keel bone can still be felt and is still the deepest point in the rounded breast. This is the amount of flesh we want to have on each bird in the flock at start of production.
- If the fleshing represents the letter W, the keel bone can hardly be felt and is bedded in the breast meat. These birds have converted their feed into meat, and became a broiler. These birds look nice, well fed, well feathered, but will hardly produce eggs.