title: A High-Concentrate Diet Induced Milk Fat Decline via Glucagon-Mediated Activation of AMP-Activated Protein Kinase in Dairy Cows.
abstract: Dairy cows are often fed a high-concentrate (HC) diet to meet lactation demands; however, long-term concentrate feeding is unhealthy and decreases milk fat. Therefore, we investigated the effects of liver lipid metabolism on milk fat synthesis. Ten lactating Holstein cows were assigned randomly into HC and LC (low-concentrate) diet groups. After 20 weeks of feeding, milk fat declined, and lipopolysaccharide levels in the jugular, portal, and hepatic veins increased in the HC group. Liver consumption and release of nonesterified fatty acid (NEFA) into the bloodstream also decreased. AMP-activated protein kinase alpha (AMPKα) was up-regulated significantly in the livers of the HC-fed cows. The HC diet also up-regulated the expression of the transcription factor peroxisome proliferator-activated receptor α (PPARα) and its downstream targets involved in fatty acid oxidation, including carnitine palmitoyltransferase-1,2 (CPT-1, CPT-2), liver-fatty acid-binding protein (L-FABP), and acyl-CoA oxidase (ACO). The HC diet increased blood glucagon (GC) levels, and liver glucagon receptor (GCGR) expression was elevated. Cumulatively, a long-term HC diet decreased plasma concentrations of NEFA via the GC/GCGR-AMPK-PPARα signalling pathway and reduced their synthesis in the liver. The decreased NEFA concentration in the blood during HC feeding may explain the decline in the milk fat of lactating cows.
authors.affiliation: Key Laboratory of Animal Physiology and Biochemistry, Ministry of Agriculture, Nanjing Agricultural University, China.
authors.forename: Lin
authors.initials: L
authors.lastname: Li
authors.affiliation: Key Laboratory of Animal Physiology and Biochemistry, Ministry of Agriculture, Nanjing Agricultural University, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Cao
authors.affiliation: Key Laboratory of Animal Physiology and Biochemistry, Ministry of Agriculture, Nanjing Agricultural University, China.
authors.forename: Zhenglu
authors.initials: Z
authors.lastname: Xie
authors.affiliation: Key Laboratory of Animal Physiology and Biochemistry, Ministry of Agriculture, Nanjing Agricultural University, China.
authors.forename: Yuanshu
authors.initials: Y
authors.lastname: Zhang
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D000214:Acyl Coenzyme A / Q000378:metabolism; D000821:Animal Feed; D000818:Animals; D002334:Carnitine O-Palmitoyltransferase / Q000378:metabolism; D002417:Cattle; D005230:Fatty Acids, Nonesterified / Q000378:metabolism*; D005260:Female; D005934:Glucagon / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D008892:Milk / Q000378:metabolism*; D047493:PPAR alpha / Q000378:metabolism; D018027:Receptors, Glucagon / Q000378:metabolism
chemical_list: D000214:Acyl Coenzyme A; D005230:Fatty Acids, Nonesterified; D047493:PPAR alpha; D018027:Receptors, Glucagon; D005934:Glucagon; D002334:Carnitine O-Palmitoyltransferase; D055372:AMP-Activated Protein Kinases