ARS | Publication request: Case Study: A snapshot of fatty acids composition of grass herbage as affected by time of day

Submitted to: Professional Animal Scientist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 23, 2008
Publication Date: December 1, 2008
Repository URL: http://hdl.handle.net/10113/22212
Citation: Gregorini, P., Soder, K.J., Sanderson, M.A. 2008. Case Study: A Snapshot in Time of Fatty Acids Composition of Grass Herbage as Affected by Time of Day. Professional Animal Scientist. 24(6):675-680.

Interpretive Summary: Modification of beneficial fatty acids in cattle products (meat and milk) depends on rumen biohydrogenation (process that nullifies the beneficial properties of fatty acids) and the net amount and composition of fatty acid consumed. Sugars and dry matter concentrations of pasture increase during the day; however, it is not known if fatty acids follow the same trend. The objective of this study was to quantify fatty acid concentrations of pasture throughout the day. Micro-pastures of orchardgrass and meadow fescue were sampled in July and September, respectively, at four times per day: sunrise; mid morning, afternoon and sunset. Pasture samples were analyzed for dry matter, crude protein, sugars, fiber content and the following fatty acids: palmitic, oleic, linoleic and a-linolenic acids. From sunrise to sunset, pasture dry matter and sugars increased; while protein and fiber decreased. Time of day did not affect pasture concentrations of palmitic, linoleic and a-linolenic acids of herbage. Oleic acid increased 22 and 12.7% from sunrise to sunset in orchardgrass and meadow fescue, respectively. However, this increment did not result in any effect of time of day on total fatty acids. Concentrations of fatty acids in grass pasture remained stable during the day, whereas fiber, sugars, and protein did not.

Technical Abstract: Manipulation of functional poly unsaturated fatty acid (PUFA) in ruminant products depends on rumen biohydrogenation and the net amount and composition of fatty acid ingested. Total non-structural carbohydrates and DM concentrations of herbage increase during the day; however, it is not known if fatty acids follow the same pattern. The objective of this study was to quantify the diurnal variation of herbage fatty acid concentrations. Vegetative micro-swards of orchardgrass (Dactylis glomerata L.) and meadow fescue (Festuca pratensis Hud.) were sampled in July and September, respectively, over two consecutive days at four times per day: 0540, 0650 (Sunrise); 1040, 1110; 1540, 1530 and 2040, 1930 h (Sunset). Cut herbage was analyzed for DM, CP, TNC, NDF, ADF, and palmitic, oleic, linoleic and a-linolenic acids. Diurnal variation of temperature, relative humidity and photosynthetic radiation were recorded every 5 min. Time of day affected (P < 0.01) herbage chemical composition. From sunrise to sunset, DM and TNC increased; while CP, NDF and ADF decreased. Time of day did not affect (P > 0.01) concentrations of palmitic, linoleic and a-linolenic acids of herbage. Oleic acid increased (P < 0.01) 22 and 12.7% from sunrise to sunset in orchardgrass and meadow fescue, respectively. However, this increment did not result in any effect (P > 0.01) of time of day on total fatty acids total fatty acid. Concentrations of PUFA in grass herbage remain stable during the day, whereas structural and non-structural carbohydrates, as well as CP do not.