Morphological, environmental and management factors affecting nutritive value of tall fescue (Lolium arundinaceum)

Abstract

The aim of this study was to quantify the relative importance of leaf age and leaf length on the dynamics of neutral detergent fibre (NDF), and 24-h in vitro digestibility of NDF (NDFD) and dry matter (DMD) of tall fescue (Lolium arundinaceum (Schreb) Darbysh.). Mini-swards were conditioned and used to conduct two experiments, the first with 4-cm plant stubble height in spring–summer 2009 and autumn–winter 2011, and the second with 4-cm or 10-cm plant stubble height in spring–summer 2011. Plants were harvested at consecutive leaf-appearance intervals to measure nutritive value up to the four-leaf stage. In parallel, leaf morphogenetic traits (appearance, elongation and lifespan) and sheath length of the successive leaves produced on marked tillers were measured. Leaf NDF contents remained stable with increasing leaf age and length but showed a marked variation across seasons. Leaf NDFD and DMD showed a consistent decrease with increasing leaf age and length, and irrespective of growing season or residual pasture height. The negative effect of leaf age and length on digestibility was related to variations in sheath tube length and associated differences in leaf appearance and elongation rates. These findings highlight the relevance of monitoring the sheath tube length as a complementary measure to leaf stage for further management of the NDFD and DMD of grass forages. Although the focus of this study was tall fescue swards, the same morphogenetic implications on forage nutritive value could apply to other temperate and tropical grass species; however, the testing of this hypothesis warrants carefully controlled investigations.

Field indicators of leaf nutritive value for perennial ryegrass and tall fescue pastures under different growing and management conditions

“…The NDF content of leaf tissue, which is the more preferred forage fraction by animals, was similar for all residual treatments, despite the fact that the leaf NDF content was slightly greater for tall fescue than perennial ryegrass, as expected from previous studies conducted at the sward level (Callow et al, ; Cullen, Bullen, Hutcheson, Jacobs, & Deighton, ; Lowe, Bowdler, Casey, & Moss, ). Also the decrease in leaf blade DMD was related to decreases in leaf tissue NDFD (Table ), as documented previously in other studies (Insua et al, ; Nave, Sulc, & Barker, ). In this study, the reported decrease in DMD and NDFD could be a consequence of physical (Wilson & Mertens, ) and chemical (Akin, ; Buxton & Redfearn, ; Jung & Allen, ) cell wall changes that are known to reduce fibre digestibility during leaf tissue ageing.…”

“…Leaf length is a “plastic” trait that is determined by the interaction between plant morphogenesis, growing conditions (mainly temperature, mineral nutrition and water status) and defoliation management (Lemaire & Chapman, ). Further, recent work at the leaf level (Insua et al, ) confirmed, for temperate and tropical grasses under contrasting seasons and swards heights, that increments in leaf blade length were closely linked to declines in leaf tissue NDFD.…”

“…To provide in each experiment swards with contrasting initial (day 0) sward structure, residual sward height treatments of 3 cm (“Low”), 6 cm (“Medium”) or 12 cm (“High”) were imposed on both tall fescue and perennial ryegrass. These sward height treatments were chosen to generate variation in plant structural traits that are likely to affect the herbage nutritive value, such as different leaf blade lengths (Insua et al, ). The three residual sward height treatments were randomly applied on perennial ryegrass and tall fescue pastures (separated areas), and assigned to main plots following a split plot design replicated across three blocks.…”

“…Furthermore, studies conducted at the leaf level indicate that the decrease in NDF digestibility (NDFD) of leaf blade tissue is the main factor responsible for declines of forage DMD of vegetative regrowth (Agnusdei, Marco, Nenning, & Aello, ; MacAdam, Kerley, Piwonka§, & Sisson, ). Two independent studies, one by Chapman, Tharmaraj, Agnusdei, and Hill () working with perennial ryegrass and the other by Insua, Agnusdei, Utsumi, and Berone () working with tall fescue, have both reported that the NDFD and DMD of leaves declined with ageing and length of successive leaves, two morphogenetic traits that can be controlled effectively through alteration of defoliation frequency and intensity (Insua, Agnusdei, Berone, Basso, & Machado, ).…”

“…Therefore, our research question is whether prevailing growing conditions and defoliation management decisions such as residual sward heights, which are known to influence pasture growth (Chapman et al, ; Insua, Utsumi, & Basso, ), leaf length (Duru & Ducrocq, ; Skinner & Nelson, ) and digestibility (Insua et al, ) of perennial ryegrass and tall fescue, affect the rates of nutritive value decline with the herbage mass accumulation and leaf stages of regrowth. This study examined whether or not observed changes of leaf nutritive value can be predicted from changes in plant structure traits such as herbage mass or leaf stage of regrowth.…”