Low protein diet supplemented with crystalline amino acids suppressing appetite and apo-lipoprotein synthesis in laying hens

There are contrary reports in the application of low protein diet (LPD) in laying hens. The present study was conducted to explore the effects of LPD on the laying performance, hepatic lipogenesis, and expression of appetite-associated genes in laying hens. A total of 240 laying hens were randomly divided into two groups: one was fed diet contains 9.2 % crude protein (LPD) and the other received 16.5 % protein (Control). LPD decreased (P < 0.05) laying rate, egg weight, egg production, and feed intake, but increased the value of feed conversion ratio (FCR). LPD treatment decreased (P < 0.05) body weight (BW) and abdominal fat weight. The plasma concentrations of triglyceride (TG) and very low density lipoprotein (VLDL) were significantly reduced (P < 0.05) in LPD hens, while glucose were increased (P < 0.05). In hypothalamus, the expression levels of neuropeptide Y (NPY) was upregulated (P < 0.05) in LPD hens, while cocaine-and amphetamine-regulated transcript (CART) was suppressed (P < 0.05). The expression of ghrelin, agouti-gelated protein (AgRP), cholecystokinin (CCK), pro-opiomelanocortin (POMC), corticotropin-releasing hormone (CRH) and melanocortin receptor 4 (MCR-4) were not changed. The mRNA levels of ghrelin in the preventriculus was suppressed (P < 0.05), whereas the expression of CCK was increased (P < 0.05) in preventriculus and jejunum. In liver, LPD increased (P < 0.05) the expression of fatty acid synthase (FAS) and acetyl-CoA carboxylase (ACC), whereas had no influence (P> 0.05) on peroxisome proliferator-activated receptors α (PPAR-α), and sterol regulatory element binding proteins 1c (SREBP-1c). In contrast to the changed mRNA levels, the hepatic activities of FAS and malic enzyme (ME) were not influenced (P > 0.05) by LPD treatment. Adversely, the expression of apolipoprotein B (ApoB), apolipoprotein very-low density lipoportein (ApoVLDL) and carnitine palmitoyl transferase 1 (CPT1) were downregulated (P < 0.05) by LPD treatment. In abdominal fat tissue, the expression of FAS, ACC, CPT1, PPAR-γ, and SREBP-1c was not altered in LPD hens, compared to control hens. In conclusion, the down-regulated NPY expression in hypothalamus is associated with the suppressed feed consumption in hens provided with LPD. The result suggests that decreased apo-lipoprotein synthesis should be at least partially responsible for the inhibited yolk-precursor synthesis and in turn the decreased laying performance.