BW and Skin Color Measurements

BW and skin color of all the males and females were measured at 6 ages: 56, 105, 150, 200, 250 (skin only), and 300 d (BW only). The color of the skin at the lateral thoracic region of each chicken was measured with a CR-400 Chroma Meter (Konica Minolta), yielding data of 3 parameters: L∗ that measured lightness (100=maximum brightness, 0=maximum darkness), a∗ that measured the balance of red and green, and b∗ measuring the balance of yellow and blue (https://www.konicaminolta.com.cn/). Additionally, at 250 d, 3 independent observers scored the visual darkness of each chicken on 1 of 3 levels (1=light, 2=intermediate, 3=dark) of the skin at the lateral thoracic region. In addition to recording each observer's score (1, 2, or 3), the average score of the 3 observers was calculated for each chicken, yielding the average visual skin darkness (AVSD) with 7 levels: 1.00, 1.33, 1.67, 2.00, 2.33, 2.67, and 3.00, as illustrated in Figure 1.

Skin photos of 7 chickens demonstrate the difficulty of visual scoring due to the continuous variation in actual skin darkness. An observer can score each chicken to 1 of only 3 levels: low (=1), intermediate (=2), and high (=3) darkness, and different observers may differently score the same chickens. Here, scores given by 3 observers to the same 7 chickens are presented. Ob.1 tended to score low darkness, giving score 1 to chickens #1 to #3, score 2 to chickens #4 to #6, and score 3 only to chicken #7. Ob.3 tended to score high darkness, giving score 1 only to chicken #1, score 2 to chickens #2 to #4, and score 3 to chickens #5 to #7. Ob.2 was intermediate, giving score 1 to chickens #1 and #2, score 2 to chickens #3 to #5, and score 3 to chickens #6 and #7. The 7 values of AVSD, calculated from the 3 scores given to each chicken, are shown in the bottom row. Abbreviations: AVSD, average visual skin darkness; Ob., observer.