ALBERT

Description: A ban on the use of antibiotic growth promoters (AGPs) has fueled and promoted scientific research towards the identification of reliable and effective alternatives. The supplementation of phytogenics AV/SSL12 (AVSSL) and Superliv Gold (SG) in water has been shown to improve broiler feed efficiency (FE) via modulation of hypothalamic neuropeptides. However, their effects on peripheral metabolic pathways are still unknown. The present study was undertaken to determine the effects of AVSSL and SG on lipid and protein metabolism-associated pathways in various tissues. Day-old male Cobb 500 chicks (n = 288) were randomly assigned to 3 treatment groups, with 8 replicates of 12 birds each. The treatment groups were fed a basal diet and supplemented with AVSSL or SG in the drinking water at a rate of 2, 4, and 7 mL/100 birds/d during the starter, grower, and finisher phases, respectively. The control group were fed a basal diet with no additive supplementation. On d 35, liver, adipose, and muscle tissue were collected from one bird per pen (8 birds/group). Data were analyzed using Student’s T-test to compare one treatment group to the control using Graph Pad Prism version 6.0 for Windows. In the liver, the levels of phosphorylated acetyl-CoA carboxylase alpha (ACCα) were significantly increased in both the AVSSL and SG groups compared to the control. The hepatic expression of sterol regulatory element-binding protein cleavage-activating protein (SCAP) was significantly downregulated in both treated groups compared to the control. AVSSL supplementation downregulated the hepatic expression of SREBP-2 and adiponectin (AdipoQ), while SG administration upregulated hepatic AdipoR1/R2 mRNA abundances compared to the untreated group. Both AVSSL and SG treatments upregulated hepatic stearoyl-CoA desaturase-1 (SCD-1) gene expression compared to their untreated counterparts. In the adipose tissue, the levels of phosphorylated hormone-sensitive lipase (HSL) at Ser855/554 site were increased in both the AVSSL and SG groups compared to the control. However, ATGL protein expression was decreased in SG compared to the untreated group. In the muscle, the levels of phosphorylated mechanistic target of rapamycin (mTOR) were increased in the AVSSL, but decreased in the SG group compared to the control. Collectively, these data indicate that supplementation of the phytogenics AVSSL and SG in water reduced hepatic lipogenesis-related proteins and increased adipose tissue lipolysis- and muscle protein synthesis-associated targets, which might explain, at least partially, the improvement in FE observed in previous research.

Description: Lipid metabolism in avian species places unique demands on the liver in comparison to most mammals. The avian liver synthesizes the vast majority of fatty acids that provide energy and support cell membrane synthesis throughout the bird. Egg production intensifies demands to the liver as hepatic lipids are needed to create the yolk. The enzymatic reactions that underlie de novo lipogenesis are energetically demanding and require a precise balance of vitamins and cofactors to proceed efficiently. External stressors such as overnutrition or nutrient deficiency can disrupt this balance and compromise the liver’s ability to support metabolic needs. Heat stress is an increasingly prevalent environmental factor that impairs lipid metabolism in the avian liver. The effects of heat stress-induced oxidative stress on hepatic lipid metabolism are of particular concern in modern commercial chickens due to the threat to global poultry production. Chickens are highly vulnerable to heat stress because of their limited capacity to dissipate heat, high metabolic activity, high internal body temperature, and narrow zone of thermal tolerance. Modern lines of both broiler (meat-type) and layer (egg-type) chickens are especially sensitive to heat stress because of the high rates of mitochondrial metabolism. While this oxidative metabolism supports growth and egg production, it also yields oxidative stress that can damage mitochondria, cellular membranes and proteins, making the birds more vulnerable to other stressors in the environment. Studies to date indicate that oxidative and heat stress interact to disrupt hepatic lipid metabolism and compromise performance and well-being in both broilers and layers. The purpose of this review is to summarize the impact of heat stress-induced oxidative stress on lipid metabolism in the avian liver. Recent advances that shed light on molecular mechanisms and potential nutritional/managerial strategies to counteract the negative effects of heat stress-induced oxidative stress to the avian liver are also integrated.