The importance of seven-day weight.

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To get the full potential out of broiler chickens it is important that the target weight at seven days

of age should be reached. As work with the Cobb500 broiler has shown, brooding is a vital period

for good overall results. Achieving good seven-day live weight will improve performance

parameters such as final live weight and feed conversion as well as maintain a low overall

mortality.

Photo: Cobb

By Dr Annsofie Wahlstrom, nutritionist Cobb-Europe Ltd

Over recent years more emphasis has been on the broiler chicken's first seven days in life. During the

first seven days 80% of the energy is used for growth and only 20% for maintenance, indicating the

importance of this period in the chicken's life. According to management guidelines for the modern broiler,

the birds are supposed to increase live weight 4.25 times during the first seven days, from approx 40g to

180g. Seven-day weight of the Cobb500 in comparison with hatch weight has increased by 300% over

the last 20 years. Good early development of the chick reaching high seven-day weights will, for example,

improve the nutritional maturity of the bird and accelerate development of the gastro- intestinal tract. Also

muscle growth and development of muscle morphology improves, as will the long-term metabolic effects.

The immune response in young chickens gets better, on the other hand delayed growth impairs

immunological capacities. As a result, final performance will be better, eg increased total growth,

improved feed conversion and better uniformity. Comparing the Cobb500 performance standards from

2008 to 2012, the seven-day live weight has increased by 8%, underlining the genetic improvement in

growth at this age.

Why seven-day-weight as a measurement?

Several different parameters can be used to determine the quality of the chick at an early age such as live

weight, growth, crop fill, body temperature, livability and mortality. Comparable parameter needs to be

objective, easy to perform, highly repeatable and inexpensive. Measuring live weight at day seven is a

well-established and accepted way of assessing pre-placement management, brooding and chick quality.

The seven-day weight has significant impact on most important parameters such as performance,

carcass and body composition. There is generally a peak in mortality at day three to four, most likely due

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to the absorption of the yolk sac in the intestine of chicks; if feed and water intake is not optimum, non-

starter/cull chicks will add to the mortality that occurs a few days later. These flocks have poorer

uniformity and increased number of small cull chicks which negatively affects growth in the first week. A

higher average seven-day weight will minimize the number of small birds that for whatever reason have

not started to eat. One concern for fast early growth is related to the risk of increased late/final mortality

due to metabolic disorders such as ascites and sudden death syndromes.

Confirmation from practice

To confirm the importance of achieving a good early development, field data was collected on as hatched

Cobb500 bird flocks within the European and African region. Case studies under Western European

conditions show that improvements of 1g at seven days correspond to 6g at 37 days of age. Gathered

data illustrates that good seven-day weight is positively correlated with high final body weight (Figure 1).

Also depending on live weight reached, there may be a bigger impact when targeting weight above 180g

at seven days of age. These data demonstrate that you may increase final weight by 80-90g when the

seven-day weight increases from 160g to 180g.

Data from the field demonstrate a positive relationship between a higher seven-day weight and total

mortality (Figure 2). These data conclude there is no increased risk of mortality due to higher early live

weights. Complete analysis of seven-day live weight and the effect on feed intake and economics has

been conducted on commercial field data. Seven-day live weights of above 180g have been shown to

improve feed conversion ratio by 10 points (Figure 3). The economic benefit of 180g weight at seven days

of age, compared with 170g and less, is an advantage in lower feed cost per kg live weight of 5%.

How to improve seven-day weight.

Seven-day weights above 180g will improve final live weight and therefore it is important to achieve these

weights. This can be done in several different ways by good chick quality, feed and management.

Dietary actions

There are several dietary actions possible to increase or secure an optimum weight at seven days. With,

for example, the chicken's gastro intestinal tract immature during the first week of age, it is important to

compose feed with:

1. Highly digestible raw materials since the chicken's enzyme system is not mature.

2. High hygiene quality of material included since the bird's immune response system is not fully

developed and a challenge might be more devastating to the young chicken compared to an older bird.

3. Optimum breed specific diets and a high quality of the feed presentation will enable the small chickens

to consume the amount needed for adequate growth.

Management actions

Below are 5 key points to help ensure optimal early broiler performance:

1. Correct brooding conditions such as temperatures, humidity and carbon dioxide level to stimulate feed

intake

2. Easy access to feed

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3. Follow up feed intake by checking the crops, 95% of the crops should be full within 24 hours

4. Pay extra attention to feed intake after four days when many disturbances occur

5. Try to reduce the percentage of small chicks by seven days by getting the necessary early feed intake

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