**3. Results**

### *3.1. Chickens' Performance*

The production results (final body weight, average daily weight gain, feed intake and feed conversion ratio) were similar in the three farms (Table 2) and there were no statistically significant di fferences that depended on the feed used (*p* > 0.05).


**Table 2.** Productivity parameters of "Parrilleros" chickens in the three farms under study (*n* = 75 per farm).

*n* = number of birds (whole flock); 1 Each value represents the mean of 3 replicates (25 birds per pen). No significant differences (*p* < 0.0) were found between farms. FBW: final body weight; BWG: average of daily body weight gain; FI: feed intake; FCR: feed conversion ratio.

### *3.2. Chemical Analysis*

Importantly, there were no significant di fferences (*p* > 0.05) in the total fat content between the 8 di fferent finisher diets used for chicken feed (Table 1). These diets were elaborated considering the composition and content of the ingredients used in each formula. In all the diets, linoleic (52.22%), oleic (24.87%) and palmitic (11.45%) fatty acids were identified as the predominant fatty acids.

The weight of fat by-products per chicken carcass was approximately 40 g, of which 65% corresponded to abdominal fat and 35% to gizzard fat. The total yield for lipid extraction obtained in chicken fat by-products was 75%.

Fatty acid profiles (% of total lipids) of chicken fat by-products from the 3 farms used in this study are shown in Table 3. No di fferences were found (*p* > 0.05) between the lipid profiles of chicken fat by-products from the 3 farms under study.


**Table 3.** Lipid profile (% of total lipids) of chicken fat by-products from the three farms under study.

The predominant fatty acids in chicken fat by-products were oleic (C18:1), palmitic (C16:0) and linoleic (C18:2) acids (Table 3), which reflects the lipid profile of the diets (Table 1). The chicken fat by-products showed a higher unsaturated fat content (65.5%) than of saturated fat (30.3%), which also reflects the values of the diets (Table 1).

### *3.3. Colour Properties*

The colour parameters of chicken fat by-products are shown in Table 4. Solid fat had statiscally higher (*p* < 0.05) L\* and a\* values than the melted and re-solidified fat. By contrast, the b\* coordinate, saturation index and hue values were higher (*p* < 0.05) when chicken fat by-products were previously melted.

**Table 4.** Colour parameters [(L\*) lightness, (a\*) redness, (b\*) yellowness, (C\*) chroma or saturation index, (h\*) hue] of chicken fat by-products (solid fat and melted and re-solidified fat).


a,b: different letters indicate significant differences (*p* < 0.05). *n* = 39.

Figure 2 presents the reflectance spectra (400–700 nm) obtained for the solid fat and the melted and re-solidified fat. As it can be seen, the shape of the spectra for both types of fat is completely di fferent. At all the wavelengths studied, solid fat showed higher (*p* < 0.05) reflectance percentages than the other fat. Melted and re-solidified fat did not show any reflectance from 400 to 480 nm (mainly corresponding to violet and blue), while from 480 to 540 nm (green) the reflectance values showed the higher increase (approx.13%), these reflectance values remaining constants until the end of the spectrum (corresponding to yellow, orange and red).

**Figure 2.** Reflectance spectra (400–700 nm) of the chicken fat by-products (solid fat and, melted and re-solidified fat).
