Defining and measuring quality in day old broilers - By Ron Meijerhof, Senior Technical Specialist, Hybro B.V., Boxmeer, The Netherlands - The quality of the day-old chick is important not only for minimising mortality in the first days of life, but also as an indicator of final performance.

This means that incubation must not only produce as many chicks as possible, but they must be of superior quality to contribute to commercial success.
However the concept of ‘quality’ is often subjective. Every hatchery manager has his or her own definition of what constitutes good chick quality, which can be difficult to describe – and even more difficult to measure.

Visual score
While visual scoring, ie. as ‘good’, ‘average’ or ‘poor’, is highly subjective, it is nonetheless a relatively accurate indicator of chick vitality. Visual scoring measures:

1. Colour: a deep yellow colour is favoured over pale (light yellow to white).
2. Development: a large, well developed, long feathered chick is considered ‘better’.
3. Navel quality: well closed navels reduce the risk of infection and mortality.
4. Vitality: alert, healthy chicks will find feed and water more quickly.

Although an experienced hatchery manager may be highly accurate in his or her visual scoring, this system is devalued by being prone to personal interpretation and difficult for other personnel to reproduce.

Tona or Pasgar score
The University of Leuven recently developed the Tona score, which was adapted by Pas Reform to create the simpler and more practical Pasgar score. Both methods apply a standardised scoring system across a range of criteria, including chick viability, yolk sac uptake, navel closure, and the ability of the chick to recover after being placed on its back, for example.

Both methods create a consistent, measurable data-set that can easily be repeated. And while the relationship between Tona- or Pasgar score and broiler performance has not yet been proven, it appears likely that there is a valid correlation to first-week survival.

Day old chick weight
Although easily recorded and repeated, day-old chick weight has limited value as an indicator of overall quality, as it is correlated with egg weight rather than chick development. This is because day old chick weight includes both the actual chick weight and the weight of remaining yolk residue. Yolk-fat is fuel for embryonic development, so if a lot of yolk remains, less development has occurred and chick quality is likely to be undermined.

Yolk free body mass
Yolk free body mass (body weight without residual yolk) is a better indicator of chick development, especially when corrected for initial egg weight . However, measuring in this way is a costly and labour intensive process.

Chick length
Measuring length from the tip of the beak to the middle toe is a more practical way to determine chick development. Hybro’s research has shown that measuring the length of a chick is a dependable indicator of development and a better indicator of broiler performance than day-old chick weight, especially when corrected for egg size.

Choosing a scoring method
The Tona- or Pasgar score and chick length have clear advantages in terms of repeatability, practical application and their relationship to chick quality. However, it is important to note that these two methods are taking different measurements.
As hatcheries are often accountable for first week mortality, the Pasgar score is useful in this environment, as hatcher conditions determine navel closure, yolk uptake and vitality – and therefore the condition of the day-old chick and its ability to thrive in the first week.
Chick length deals more with development, which is related to conditions in the setter, and has less influence on first-week survival but more on performance during grow-out. This method is therefore recommended for total integrations whose bottom-line is determined by broiler performance.
A combination of the two methods, with ± 75 per cent of the final score based on broiler growth potential (chick length) and the balance based on survival rate in the first week (Pasgar score), provides optimal measurement of chick quality.

This column was published in International Hatchery Practice Volume 19 Number 7, 2005

Source: Hybro B.V. - June 2006