2.2.1. Learning Test

The learning test was conducted in a T-maze, as previously detailed, with a slight change [21]. Briefly, at 49 and 50 days, 10 female birds in two batches randomly selected from each treatment were marked with a 16 mm foot ring and deprived of food from 18:00 the day before the test and water for 3 h during the testing. The area connected to the start box was 200 cm long, and it was 40 cm wide at the end, where the end turning a 90° to the left or right was located, followed by another 120 cm long arm (Figure 1). The chicks were habituated to the T-maze for 1 h, and there was regular food with live worms available at both ends of the maze during this time. Testing was conducted during the daytime, and food was situated at the far end of one of the arms, out of the chick’s sight. For a test bird, the food was always situated at the same end of the maze, and the direction was balanced in the test. Each test session was recorded by video, until the bird found the food and had fed for 30 s or a maximum of 10 min. The chick was considered to have made a choice when it reached the end of either arm. When a bird chose the objective arm (food existed) first in five out of six consecutive test sessions, it was considered to have solved the task, was recorded as “success” and then was returned to its pen. Birds that failed to habituate and did not reach the food during the initial test session were returned to their home pens, recorded as “failure”, and replaced with a different bird.

Dimensions of the T-maze. Height of the T-maze: 100 cm.