Effects of induced cold stress on eggs during incubation on hatchability, incubation time, and chick quality

Mariem Saidani; Amani Askri; Manel Ben Larbi; Naceur M'Hamdi; Amal Hazmi; Adnene Haffar

Mariem Saidani Higher School of Agriculture of Mateur
Amani Askri Research Unit of Ecosystems & Aquatic Resources, UR03AGRO; National Agronomic Institute of Tunisia, 1082 Tunis, University of Carthage, Tunisia
Manel Ben Larbi Research Unit of biodiversity and resource development in mountain areas of Tunisia, UR17AGR14; Higher School of Agriculture of Mateur, 7030 Mateur, University of Carthage, Tunisia.
Naceur M'Hamdi Research Unit of Ecosystems & Aquatic Resources, UR03AGRO; National Agronomic Institute of Tunisia, 1082 Tunis, University of Carthage, Tunisia.
Amal Hazmi Research Unit of Ecosystems & Aquatic Resources, UR03AGRO; National Agronomic Institute of Tunisia, 1082 Tunis, University of Carthage, Tunisia.
Adnene Haffar The Tunisian Poultry Farming Company Avenue de la jeunesse, 2084 Borj Cedria , Tunisia.

Keywords: Keywords: cold stress, hatcher, egg weight loss, incubation time, hatchability, day-old chick quality.

Abstract

The incubation environment, temperature in particular, is a key determining factor influencing embryonic development, hatchability and chick quality in broiler production. This study aimed to evaluate the effects of induced cold stress during the endothermic and exothermic phases of incubation on egg weight loss, incubation duration, hatchability, and day-old chick quality. The objective was to determine whether short and controlled reductions in incubation temperature could improve chick quality without negatively affecting hatching success or incubation time.

In total, 1350 fertile eggs from broiler breeders aged 45 and 46 weeks, representing the peak laying period, were used. Eggs were randomly assigned to three treatment groups. The control group was incubated at standard commercial incubation temperature throughout the incubation period. The first experimental group (E1) was exposed to a cold stress of 25–26 °C for 3 hours starting on day 6 of incubation, from the endothermic phase, until day 18. The second experimental group (E2) was subjected to the same cold treatment beginning on day 14 of incubation, corresponding to the exothermic phase, until day 18. Egg weight loss, incubation time, hatchability, and chick quality at hatch were evaluated. Chick quality was assessed using the Tona scoring system.

Exposure to intermittent cold stress significantly reduced egg weight loss compared with the control group. The average egg weight loss was 10.86% in E1 and 10.99% in E2, while the control group recorded 11.27%. Chick body weight at hatch improved in both experimental groups, with average weights of 62.8 g in the control group, 68.25 g in E1, and 65.9 g in E2. Chick quality scores also improved following cold treatment. The proportion of chicks achieving the maximum Tona quality score was highest in E2 (39.6%), followed by E1 (35.4%) and the control (33.3%). In contrast, hatchability and incubation duration were not affected by the cold exposure, indicating that this controlled cooling procedure did not impair overall incubation performance.

These findings demonstrate that short-term cooling applied at specific phases of incubation, particularly during the exothermic phase, can enhance chick quality and body weight at hatch without affecting hatchability or incubation duration. Given the link between day-old chick quality and later performance, controlled cooling may represent a valuable strategy to optimize incubation practices.