Daily Losses of Forage Nutritive Value in Strata of a Mixed Cool-Season Grass Sward During Grazing.

Ruminants tend to be selective, grazing forage that is higher in digestibility and protein, with a lower percentage of fiber than the residue remaining. Animals are also selective when introduced to a fresh rotationally stocked pasture when compared to an ungrazed pasture. Consequently, high variation in animal output occur, due to the rapid changes in selectivity within a rotationally stocked pasture. The objective of this research was to characterize the daily shifts in vertical distribution of herbage mass and nutritive value within a grass sward under rotational stocking management. This information might be useful in predicting the effect that forage canopy removal will have on the nutritive value of the forage remaining at time intervals during a daily grazing period. The research was conducted at Columbus, OH on three different dates in 2009 and 2011. Six spots were randomly selected for collecting forage samples. Samples to characterize the nutritive value in strata (10-cm vertical layer) were collected immediately before the animals were introduced into the paddock and subsequent sampling occurred after the first, third and sixth hour of grazing. Morphological composition of the sward was quantified and forage quality analyses were conducted on the samples. Forage nutritive value changed throughout the day. The results suggest that neutral detergent fiber (NDF) concentration does not change at the same rate as in vitro true digestibility (IVTD) and NDF digestibility (NDFD) of the forage during first six hours of a grazing event within rotationally stocked pastures.