Seasonal Changes in Forage Quality in Strata of a Mixed Cool-Season Grass Sward.

Energy availability from forages is limited by fiber concentration which is the primary constituent of plant cell walls. Fiber is usually measured by the neutral detergent fiber concentration, varying between 50 and 70% NDF in cool-season grass species. Forage nutritive value is primarily affected by maturity, but also by the environment and plant morphological characteristics, such as leaf:stem ratio. Studies on forage quality in stratified alfalfa canopies have concluded that attempts to improve forage quality of alfalfa should be directed towards the lower part of the canopy. However, information is lacking regarding quality changes within strata of cool-season grasses. The objective of this study was to analyze changes in forage quality of a mixed cool-season grass sward throughout the growing season in Ohio and its relationships with maturity and plant morphological characteristics. This information will be useful for explaining changes in nutritive value of the forage across the season and will serve as a basis for grazing management recommendations to optimize forage nutritive value. The hypothesis is that there is a strong relationship between grass sward nutriitive value and time of year, age, maturity, available forage, and nutritive value of the canopy strata. The research was conducted at Columbus, OH, from April to October 2009 and 2010. Treatments consisted of five different dates of initiation of growth (clipping dates) in a mixed cool-season grass species sward, replicated 4 times in a randomized complete block design. Samples to characterize the nutritive value of the sward canopy were randomly collected weekly from each experimental unit and the procedure was to collect samples from lower stubble to a 5-cm height and from every 10-cm vertical strata of the offered forage. Morphological composition of the sward was quantified and forage quality analyses were conducted.