Linseed Cake Supplementation Increases Tissue n-3 PUFA Levels but Reduces Growth Performance in Broiler Chickens at Higher Inclusion Levels

This study evaluated the effects of dietary linseed cake on the fatty acid profile of meat and abdominal fat, and on growth performance in broiler chickens. A total of 198 birds were randomly allocated to three groups (66 birds/group). The control group (C) received a standard soybean meal-based feed, while the LIN6 and LIN12 groups were fed diets that were supplemented with 6% and 12% linseed cake, respectively. Linseed cake supplementation reduced saturated and monounsaturated fatty acids, increased n-3 polyunsaturated fatty acids (PUFAs) in meat and abdominal fat, and lowered the n-6/n-3 PUFA ratio (FDR-adjusted p < 0.05). The 12% inclusion resulted in a more pronounced accumulation of n-3 PUFAs—4.3–5.0 times higher than the control—while 6% inclusion increased n-3 PUFAs by 2.8–3.3 times (FDR-adjusted p < 0.05). However, 12% inclusion negatively affected growth performance, reducing body weight by 9.9% and feed intake by 10.4% at 42 days (p < 0.05), whereas the 6% inclusion had no adverse impact (p < 0.05). These results indicate that 6% linseed cake represents the optimal practical inclusion level, effectively enhancing the n-3 PUFA profile of broiler meat and abdominal fat without compromising growth, while higher inclusion levels may impair production performance.