Measurement vs. observation: recognising the comfort status of day old chicks

BT measurement in day-old chicks has become fashionable, possibly because many new hatchery managers are more familiar with this technique than looking at behaviour.

When checking BT, the hatchery manager must decide:

1. What is the most reliable method of measurement?
2. What is practical for application in field conditions?
3. How will the resulting records be useful to the hatchery?

The physiological mechanism for maintaining BT develops late in the chicken, at around day 3 of life. Until then, the chick’s physiology is largely dependent on its environment, much like that of a cold-blooded animal, eg. a reptile. Measuring BT in the day-old chick is therefore more a reflection of climate conditions: temperature, humidity and the wind speed of an environment. Deviation from the standard means either that the chicks were exposed for long enough to a chilling effect or that they got overheated. Both situations can be also observed in the chicks’ behaviour. Huddling, gathering close to each other and peeping loudly indicate cold distress, while open wings and beaks and panting are typical symptoms of overheating. When chilled, the feet get cold first, which can be ‘tested' by touching ‘chick to cheek’. Fluctuation of BT can still be seen when the chicks remain quite comfortable: just 30 minutes from take-off in the warm chick handling room is enough to reduce BT by 0.5 °C, which causes no signs of discomfort in the birds. This instability has prompted the use of a conventional veterinary thermometer to measure BT internally (per rectum), with the logic being that more stable results can be expected from an internal measurement than on the surface of the chick’s body.

To verify this thesis, two methods have been compared in a field trial: measuring BT on vent by an IR-ear thermometer (eg. Braun ThermoScan) and by a conventional thermometer inside the rectum. The trial showed that:

• Measurements taken by both methods depend heavily on environmental conditions.
• Results in both methods show variation, for example due to the presence or lack of fluff coverage on the vent area when measuring with an ear thermometer, or the depth of insertion if using a conventional rectal thermometer.
• Accuracy expressed by a spread of results is similar for both methods of measuring BT. Taking 3 correct measurements on the same chick the same spread of about 0.2 °C was seen.
• Measurement taken by an ear thermometer is on average approx. 0.5 °C lower than when measured on the same chick by rectal thermometer for deep body temperature.
• Measuring by an ear thermometer is more practical. Taking one measurement requires 5 seconds while taking a single rectal measurement takes 25-30 seconds and is very stressful for the chick.

Advice

• Observing the birds’ behaviour gives accurate and direct information about the current comfort status of chicks
• Measuring BT of day-old chicks is best viewed as just a supplementary way of describing their status. As the result can be expressed numerically, it can serve to document extreme situations eg. in relation to claims.
• Use an IR-ear thermometer if measurement is required. It is easier, faster and less distressing for the chick. More measurements can be taken without compromising accuracy.
• Measuring chick BT as a standard procedure in evaluating chicken quality is unnecessary.