In vitro digestibility response of cocksfoot (Dactylis glomerata L.) to growth and defoliation: a simple model

Abstract

Herbage digestibility, which to a large extent governs the animal's intake, is not easily predicted for grazing animals, and can vary due to different grazing managements. The objective of this study was to build a model for a range of defoliation managements, which takes account of vegetative grass tiller structure, rather than dates of cutting or grazing, as done usually. An experiment was conducted in 1997, near Toulouse, to examine the digestibility of cocksfoot whole lamina and lamina segments (15 cm) for three defoliation regimes. These regimes mimicked severe and lenient intermittent defoliations plus a frequent defoliation treatment over a six-week period. Data were collected for (i) lamina mass and digestibility for the youngest expanded lamina, (ii) lamina appearance rate, lamina and sheath lengths.Laminae digestibility, measured over time, varied greatly with the defoliation regime both for the youngest full expanded lamina and all laminae on a tiller. Digestibility of the youngest fully expanded lamina decreased from one leaf insertion level to the next, but this decrease was lowest when the defoliation regime was frequent. There was also a consistent decrease in the digestibility of a lamina from its tip to its base. Sheath and lamina lengths varied with treatment in a different way to lamina digestibility. During frequent defoliation, sheath and lamina lengths both increased slightly while they showed substantial increases in the two other treatments. Lamina length increased from one insertion level to the next, and resulted in the addition of less digestible lamina segments rather than reducing overall lamina digestibility. Sheath length, through its influence on leaf appearance rate and lamina length, could be used to predict the digestibility of laminae over time according to leaf insertion level and the difference in the digestibility observed from the tip to the base of a particular lamina. Sheath length could therefore provide a basis for predicting the time course of grass digestibility for different combinations of defoliation frequency and height.

Effect of nitrogen fertiliser rates and defoliation regimes on the vertical structure and composition (crude protein content and digestibility) of a grass sward

“…For cocksfoot at the end of spring it is about 3 weeks. 24 This resting time is close to recommendations. This is why the target residual sward height usually increased when the sward height before grazing increased too, 31 and there is a trend to increase the residual sward height recommendations throughout the grazing season to avoid grazing the sheath layer.…”

“…25 These changes were also in agreement with observations made at the leaf scale. 15,24 Thus the herbage composition per layer was a result of the gradient along a leaf and of the difference between successive leaves on a tiller. 16,23,26 The difference in digestibility between laminae at different insertion levels results from the addition of less digestible segments rather than a reduction in overall lamina digestibility.…”

“…16,23,26 The difference in digestibility between laminae at different insertion levels results from the addition of less digestible segments rather than a reduction in overall lamina digestibility. 24 Two reasons may be offered to explain the continuum in herbage composition between lamina and sheath components. First, there is at least one layer which contains a mixture of sheaths and laminae.…”

Biomass flow and defoliation pattern in alexandergrass fertilized with nitrogen

“…According to Duru, Feuillerac and Ducrocq (1999), for a given level of N, under stable weather conditions, the phyllochron depends on the leaf blade length of the preceding leaf. The highest leaf appearance rate and the lowest phyllochron, observed in the first period, determined the maximum number of green leaves per tiller at that time.…”

The use of herbage nitrogen status to optimize herbage composition and intake and to minimize nitrogen excretion: an assessment of grazing management flexibility for dairy cows

“…The changes in DM digestibility of herbage are assessed according to N fertilizer supply and the grazing interval, which lies between Min[GI max , GI¢ max ] and Max[GI min , GI¢ min ]. The leaves are also longer (Duru et al, 2000a) and less and less digestible as the sheaths grow longer (Duru et al, 1999b). During regrowth, leaves appear more and more slowly (Duru et al, 1999a).…”