- In broiler chickens, hepatic lipid metabolism plays a significant role in whole body and muscle fatty acid (FA) incorporation. Flax seed is a rich source of α-linolenic acid and can be used to increase n-3 FA in poultry meat. Previous studies have shown that flax seed in combination with carbohydrase enzymes in broiler diets enhances long chain (LC) n-3 FA in hepatic tissue. Three experiments were conducted to evaluate the effect of flax seed and carbohydrase enzyme addition on production performance, total tract lipid digestibility, hepatic fatty acid composition, liver lipid class distribution and lipid metabolism in broiler chickens.
In Experiment 1, broiler chicks were placed in individual cages and fed isocaloric, isonitrogenous corn-soy diets: Control, Flax (10% flax), and Flax+E (Flax+0.05% enzyme). The diets were fed for a period of 42 days. Total tract digestibility of lipids and FA were assessed from day 19 to 21 of growth. There was no effect of diet on production performance characteristics, including final body weight (BW) or yield of cut-up parts. Flax-based diets reduced total tract lipid digestibility (p<0.001), increased excreta dry matter and total lipids compared to Control (p<0.05). Addition of enzyme led to an increase in digestibility of n-3 FA when compared to Flax (p<0.001). Total lipids in the liver tissue was higher in Flax-fed birds (p=0.044). Liver tissue of Flax and Flax+E
were enriched with n-3 FA along with a reduction in n-6 FA (p<0.05) compared to Control. Hepatic tissue of Flax+E exhibited higher monounsaturated FA compared to Flax and Control (p<0.05).
In Experiment 2, tissue (heart, cardiac) was collected from broiler chicks raised in floor pens and fed isocaloric, isonitrogenous corn-soy diets: Control, Flax (15% flax), and Flax+E (Flax+0.05% enzyme). The diets were fed for a period of 35 days. Hepatic and cardiac tissue lipids were subjected to triglyceride (TAG) analysis. Lipid classes (TAG; phosphatidylcholine, PC; phosphatidylethanolamine, PE) from hepatic crude lipid extract were separated and subjected to FA analysis. TAG was lowest in hepatic tissue of Flax and Flax+E compared to Control (p=0.001). Flax+E TAG was observed to incorporate significantly lower total saturated FA and increased monounsaturated FA compared to Control. Total n-3 FA were greater in all lipid classes in Flax+E compared to both Flax and Control (p<0.05). A 3-fold and 2-fold increases in LC n-3 FA was observed in PE and PC, respectively of Flax+E compared to Control.
In Experiment 3, liver tissue collected from Experiment 1 were subjected to lipid metabolism related gene expression studies. Expression of peroxisomal acyl-CoA oxidase 1 (ACOX1), acyl-CoA synthase long-chain family member 1 (ACSL1), and carnitine palmitoyltransferase 1 A (CPT1A) was up-regulated in Flax+E birds (p<0.05). Fatty acid synthase (FASN) and acetyl-CoA carboxylase α (ACCA) were significantly reduced in Flax and Flax+E (p<0.05). Sterol regulatory element-binding transcription factor 1 (SREBF-1) target fatty acid desaturase 2 (FADS2), a key-regulator of LC FA
synthesis, was down-regulated in liver of Flax-fed birds. No effect of diet was observed on FA transport gene expression.
Overall, these studies suggest that n-3 FA supplementation and carbohydrase enzyme addition affects lipid digestibility, hepatic lipid class distribution and metabolism of broilers.