Controlling your body weight

By Ron Meijerhof, senior technical specialist, Hybro B.V. Modern broiler breeders are very efficient in producing hatching eggs. Where 10 years ago production peaks of 80% were considered to be good, at this moment peak productions above 85% are not uncommon, and peaks as high as 90% are observed.
calendar icon 26 February 2007
clock icon 11 minute read

Although we see in general that heavy, high yielding broiler breeders tend to have a somewhat lower production than the lighter, more classical orientated breeds, also these birds can reach high peaks if the management is done correct.

However, we do see that sometimes the persistency of production is impaired, especially with these high yielding, fast growing lines. Not only the egg production declines sometimes faster than expected, but also the fertility drops more than the norm. This drop in egg production and fertility is often related with an increase in body weight after peak. If the birds grow after peak, the majority of this growth will be in body fat. This fat content has a negative effect on persistency, as the birds will have a problem keeping the formation of follicles and eggs at maximum level. At the same time, fertility is impaired as the storage of semen in the hens becomes more difficult and mating frequency goes down. This fertility drop is often seen as a male effect, but also the females can have an influence, especially if overweight is occurring. To control the body weight a strict feed management has to be applied, and we will look a bit further into the requirements for this.

Why to reduce

Broiler breeders have all the genetic components of broilers. Of course the genetic make up of the final product is divided over males and females, but both will have quite a large quantity of broiler traits in their genes. Although we consider broiler breeder females as egg laying birds, we have to realise that they represent more of a broiler bird than of an egg layer type bird. This does not mean that the birds can’t produce eggs, as modern peak productions show, but it means that if the birds have a choice, they probably choose for producing meat instead of producing eggs. The question is how we let them choose for eggs, and after they have made the choice for eggs, how do we control them so they keep on laying and don’t turn into overweight birds.

Growth requirements at different stages

Over the period of a breeder’s life, the growth requirements are not the same all the time. During rearing, we know that a bird has to grow approximately 90 to 100 grams a week, with a slightly higher growth at the end of rearing to get the birds ready for production. This growth will be mainly protein, as the birds during rearing hardly will grow any fat, the feed restriction is simply to severe for that. Next to the protein, the bird will also grow bones, especially in the first part of rearing. Before a bird comes into production, it has to make a growth jump of about 300 grams in approximately 10 days. This is to allow the liver to fill up with nutrients for egg formation, to develop the reproductive tract and to actually form the first follicles. This growth is partly fat and partly protein. If a bird does not make this growth jump, it will not start to produce. Once the bird has made the growth jump and actually produces eggs, only a little growth is necessary to keep the birds in production. In fact that growth can be close to zero, but the risk of loosing weight becomes too severe, so a little safety margin of approximately 5 to 10 grams of growth per week will be beneficial. This growth will be mainly fat. If we feed the birds more than necessary for this amount of growth, it will turn it into body weight. As the bird is in principal not an egg laying bird but a broiler, it will not put surplus feed into eggs, but into body weight.

Birds in a group

We must realise that a flock of birds is actually a group of birds in different stages of development. Although we consider all birds to be equal, in reality they are not. That shows best at start of production. If a bird starts its production, when it decides to change from growing into reproduction, it rapidly inclines from no production to a high level of daily egg output. However, a flock takes about 6 weeks to come from start of production into peak. This is because the individual bird might come into full production within a couple of days, but not all birds come into production at the same moment. If that was the case, we would jump up from no production to peak within a couple of days.

This means that at every given stage of our increase in production, the percentage of birds that are in rearing, coming into production and are already in production is changing.

A flock in percentages

How does that work out in a group of birds? If we are just before start of production, we have a number of birds that are already making the jump of 300 gram in body weight to start produce eggs next week. No birds are in production yet, and the remaining birds will be still in rearing, needing a growth of approximately 100 grams per week.

If we have 50% production, we expect the next week the production to increase with 20-25%. That means that 50% of the birds are in production, needing a growth of 5-10 grams of fat per week, 20-25% of the birds are making the jump of 300 grams, and the rest of the birds are either in rearing, or have decided they will not produce at all. As we don’t want to cut the birds short, we consider that all birds will become productive, and that means that we assume that 25-30% of the birds are still in rearing.

If peak is 85%, at that moment no birds are making the jump anymore, no birds are in rearing, but all birds have to grow 5-10 g to stay in production.

From these kind of estimations we can calculate what the flock has to do on average body weight, but also what the required feed amounts will be in the different periods.

When the calculations are done, it shows that the amount of feed to keep a flock in production is substantially lower than to get a flock into production, because no birds need to make the jump of 300 grams in body weight anymore, and no birds have to grow 100 grams because they are still in rearing.

This means that we have to think about cutting feed at the time the last birds have made the jump in body weight. If we don’t do that, the birds will use this extra feed for growing, and the flock will gain more body weight than the required 5-10 grams, impairing persistency and fertility in a later stage.

If we wait with cutting feed, the birds will use that extra feed for putting on body weight. This body weight needs to be maintained, requiring higher levels of feed. This means that cutting feed later is more difficult, as there is more body weight to maintain.

When is peak

An important point in the process of taking feed away is the moment of actual peak production. The question is how to determine peak. We can define peak as the moment when the last birds have started to produce. This means that if the last birds are making the jump and start to produce, peak has been reached. As all the birds from that moment on only need to grow 5-10 gram, feed reduction can start from there.

If we look at a normal production pattern, we often see that the last significant weekly jump in production is for instance from 79 to 85%. Although the production can still go up with 1 or 2 percent after that, we must realise that at this moment, all birds have made the jump in body weight to come into production, or are about to finish the jump. This means that peak is reached after the last significant weekly increase in production, where significant means a jump of at least 3 or 4%. Another 0.5 or 1% extra production a week later doesn’t really alter our definition of peak, because these few birds were already in the process of coming into production. Because we are still feeding as if a significant percentage of birds is making the body weight jump, gently start cutting feed from that moment onwards will not cause a big problem for these birds.

In practice, we often wait until the actual production goes slightly down, before we determine that the peak has been reached and reduction of feed can start. What we have to realise is that by doing that, we are already several weeks feeding the birds as if a percentage of the birds is still making the jump in body weight. As this is actually not the case, the birds will use that feed for extra growth.

How to reduce

In theory, it is possible to cut several grams of feed at the very first moment the last birds are in the process of making the jump in body weight. This means in practice that the feed can be reduced while the flock is still slowly coming up in production. As a lot of people will find it difficult to cut feed on a flock that still seems to increase in production, this is too severe to do in a field situation.

However, cutting the feed at the moment the production starts to go down is too late, as a part of the peak feed is actually meant to allow the last birds to make the body weight jump into production, and at that moment already for several weeks no bird is making that jump anymore.

A good rule of thumb is to start cutting feed after a limited number of weeks at peak feed. Normally we give peak feed at 65-70% production, because from that moment onwards we need about two weeks to reach peak. This means that we give the maximum feed to allow the last group of birds to make the body weight jump.

But this also means we can slowly start to cut the feed if the last birds have made the jump, so about 2 to 3 weeks after reaching peak feed. Although it seems not a big reduction in feed, in reality we are pulling the feed away after 2-3 weeks of peak feed, instead of the usual 6-7 weeks of peak feed. Even if we pull feed with 1 gram per week, so a moderate schedule, the difference in timing will give us a difference of 4-5 grams of feed at the time we normally would have started pulling the feed.

Although 4-5 grams will sometimes not be enough to really get the birds under control, it is a good way to avoid excessive body weights later on.

If we feel more comfortable with these levels of feed cuts, an initial cut of 2 or 3 grams can be considered. If we do that, all of a sudden we are not cutting 4-5 grams, but 6 or 7 grams, which can be enough to give us good control.

One of the advantages of this system is that we start to reduce feed early, before the birds put it in body weight and we find out that we have to maintain the feed at a high level to maintain body weights.

Risk of reducing

Reducing feed bears always the risk that we cut the feed too much and that the bird as a result starts to drop production. This is the main reason why people often wait with cutting feed until the production starts to go down.

However, the risk of reducing feed is bigger if we cut the feed late, because at that moment there is more body weight to maintain. A good control to see if we are still on the safe side is body weight increase. As long as the body weight of the individual bird will not drop, the production will continue, as the birds have enough left over for the egg. To allow all individual birds to at least not drop body weight, the average flock has to have a minimum amount of growth of about 5 to 10, maximum 15 gram. 5 gram will be sufficient in well controlled conditions, 15 grams might be needed if more variation in uniformity, feed quality, climatic conditions etc is expected.

Not reducing the feed sufficiently after peak will result in an increase in body mass and especially in body fat, and that forms a risk for production and fertility.

February 2007

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