Duodenal infusion of fatty acids differentially affects plasma glucagon-like peptide-1 and ghrelin concentrations in sheep.

The aim of this study was to investigate how intraduodenal infusions of fatty acids (FA) affect appetite-related gut peptides such as glucagon-like peptide-1 (GLP-1) and ghrelin in sheep. We hypothesized that these peptides can be highly reactive to unsaturated long-chain FA, because they are well known to decrease dry matter intake (DMI). Four ewes were fitted with a duodenal cannula and a jugular vein catheter for a 6-h duodenal infusion of the 9 FA (C8:0, C10:0, C12:0, C14:0, C16:0, C18:0, C18:1, C18:2, and C18:3) and water (control). The concentration of each FA was 1.6 g per metabolic body weight (BW), approximately corresponding to the amount of supplemented fat in a standard dairy cow diet. Each infusion was separated by at least 2 d. During the infusion period, blood samples were collected periodically to determine changes in plasma GLP-1, ghrelin, and metabolite concentrations. Duodenal infusions of C18:1, C18:2, and C18:3 led to higher plasma GLP-1 (P < 0.05) and lower glucose (P < 0.05) than control. Plasma ghrelin concentrations were greater in C18:1 and C18:3 infusions than control (P < 0.05). Plasma ketone bodies were higher in C8:0 and C10:0 infusions (P < 0.05), but plasma triglyceride concentrations were lower in C8:0, C10:0, C12:0, and C16:0 infusions (P < 0.05) than control. Fatty acid infusions except for C18:3 led to higher plasma NEFA concentrations than control (P < 0.05). These results confirmed that the hypophagic effect of dietary unsaturated long-chain FA is mediated by GLP-1 (an anorexigenic effect) secretion. However, we also observed higher plasma ghrelin (an orexigenic effect) partially by unsaturated long-chain FA. Thus, the gut peptide secretions when ruminant animals ingest FA supplements would complexly affect satiety and further studies are needed to determine their each impact on DMI.

Effect of increased feeding of dietary α-linolenic acid by grazing on formation of the cis9,trans11-18:2 isoform of conjugated linoleic acid in bovine milk.

Feeding systems such as grazing affect the fatty acid profile of bovine milk fat. In addition, milk fat is formed as the product of fatty acid metabolism in cow bodies before being secreted into milk. However, how grazing influences milk fatty acid profile through the metabolism has not been completely characterized. When fatty acid concentrations in Holstein milk were compared between grazing and non-grazing periods, α-linolenic acid was significantly higher in the grazing period than in the non-grazing period. This could be explained with an increase in α-linolenic acid feeding with grazing. α-linolenic acid had a linear positive correlation with conjugated linoleic acid (9c,11t-18:2) (CLA) and vaccenic acid (VA) during the grazing period, whereas CLA had higher correlation with linoleic acid rather than with α-linolenic acid during the non-grazing period. These data indicate that the high content of dietary α-linolenic acid affects CLA and VA formation in milk of grazing periods via α-linolenic acid metabolism into VA.