ARS | Publication request: A snapshot in the effect of time of day on herbage toughness and chemical composition

Submitted to: Animal Feed Science And Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 24, 2009
Publication Date: May 26, 2009
Repository URL: http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6T42-4VXT0W7-1-3&_cdi=4962&_user=209810&_orig=browse&_coverDate=05%2F26%2F2009&_sk=998489996&view=c&wchp=dGLbVtz-zSkWz&md5=3b90ff2dd134f35e13908434307be30e&ie=/sdarticle.pdf
Citation: Gregorini, P., Soder, K.J., Sanderson, M.A., Ziegler, G.R. 2009. Toughness, particle size and chemical composition of meadow fescue (Festuca pratensis Hud.) herbage as affected by time of day. Animal Feed Science And Technology. 151(3-4):330-336.

Interpretive Summary: Pasture chemical composition varies throughout the day; however, it is not known if this variation affects pasture physical (mechanical) properties such as ‘toughness’. The objective of this study was to quantify changes in toughness and particle size reduction properties of pasture in relation to changes in pasture chemical composition throughout the day. Micro-pastures of meadow fescue were sampled at four times of day: 0650 (sunrise), 1110, 1530 and 1925 h. Samples were analyzed for dry matter, crude protein, total non-structural carbohydrates (energy), neutral and acid detergent fiber, toughness and particle size reduction properties. Time of day affected pasture chemical composition. From morning to evening (0650 to 1925), dry matter and total non-structural carbohydrates increased, while crude protein, fiber and toughness decreased. Also from morning to evening, pasture was more readily broken down into smaller particles. Toughness was negatively associated with dry matter and total non-structural carbohydrates content and positively associated with percentage of fiber. These results suggest that pasture physical-mechanical features may depend on time of day. Pasture grazed during the evening hours may be more easily chewed and digested.

Technical Abstract: Herbage chemical composition varies diurnally; however, it is not known if this variation affects herbage biomechanical properties. The objective of this study was to evaluate potential changes in herbage toughness and particle size reduction index (PSR) in relation to diurnal fluctuations of herbage chemical composition. Vegetative (tillers with 3 fully expanded leaves) micro-swards of Festuca pratensis Hud. were sampled at four times of the day: 0650 (sunrise), 1110, 1530 and 1925 h. Cut herbage was analyzed for dry matter (DM), crude protein (CP), total non-structural carbohydrates (TNC), neutral and acid detergent fiber (NDF, ADF), toughness and PSR. The experiment was repeated on two consecutive days. Diurnal variation of temperature, relative humidity and photosynthetic radiation were recorded every 5 min with an automated weather station. To characterize the relationship between dependent variables, Pearson correlations were performed. Time of day affected herbage chemical composition. From 0650 to 1925, DM, TNC and PSR increased (P < 0.05), while CP, NDF, ADF and toughness decreased (P < 0.05). Toughness was negatively correlated (P < 0.05) with DM and TNC concentrations, and positively correlated (P < 0.05) with percentages of NDF and mainly ADF. The PSR was positively correlated (P < 0.05) with DM and TNC concentrations, and negatively correlated (P < 0.05) with percentages of NDF, ADF and toughness. These results suggest an effect of time of day on herbage toughness and PSR as a function of increases in DM concentration and reductions of NDF and ADF percentages due to an increase in TNC. Diurnal fluctuations in chemical composition of herbage not only result in differential nutrient supply to grazing ruminants during the day, but also in temporal fluctuations in herbage biomechanical features.