Digestibility and chemical composition of fractions of lucerne during spring and summer

Abstract

Bulk harvests of primary growth were made at intervals during the spring and summer of 2 consecutive years from an ungrazed area of lucerne (Medicago sativa) and the digestibility by sheep was measured. At the same times, shoots of known length representative of the sward were collected, divided into 7-5 cm lengths, and separated into leaf and stem for the determination of ash, nitrogen, cellulose, and in vitro organic matter digestibility.Digestibility and leaf: stem ratio of the bulk harvests decreased and dry matter increased as the season advanced. Leaf composition changed little, but stem increased in lignin and decreased in ash and in vitro digestibility. In vitro digestibility and leaf: stem ratio were highly correlated with sheep digestibility.Chemical composition of shoots of known heights was similar to that of the bulk harvests. Leaf weights/shoot tended to increase linearly with height of shoot, whereas stem increased nearly as the square of the height. Dry matter of leaf and stem were inversely related to leaf:stem ratio. Stem digestibility decreased with leaf:stem ratio and with increase in shoot height.Chemical components of shoot fractions were associated with each other and were largely dependent on the distance from the top of the shoot at which they had been taken, irrespective of shoot height or time of year. Bottom stems had lower ash, nitrogen and digestibility but higher cellulose, dry weight and dry matter than top stems, whose composition approached that of leaves. Leaf fractions showed little consistent trend with position on the shoot.Some of the difficulties in studying changes in plant composition under field conditions are discussed. INTRODUCTIONreported by Mowat et al. (1965a, 6) to be similar; they suggested that digestibility might be preDespite the large niunber of chemical analyses dieted on a date basis by adjusting for particular which have been carried out on lucerne (Medicago year effects. sativa), information on the comparative nutritional The nutritive value of the material eaten by the value of various parts of the plant at different grazing animal may be greatly influenced by the times of the year is limited. Terry & Tilley (1964) height and stage of growth of the pasture and by divided lucerne stems into 6 in lengths and found the degree of selection, and cannot be determined that there was a progressive decline in digestibility merely by whole plant analysis. This paper reports from top to bottom, though the digestibilities of work carried out during two seasons, in an attempt equivalent stem fractions in young and mature to characterize more clearly plants at different stages plants were very similar. Davies (1963) observed of growth so that general predictions of the quality that as the season advanced and plant height of herbage available to the grazing animal might be increased, the leaf and upper third of the stem made. maintained high digestibilities, but formed a de-MATERIALS AND METHODS creasing portion of the total yield; the lower stem fell steeply in digest...

Effects of plant architecture and drought stress level on lucerne forage quality

“…Several studies have reported greater decrease in forage quality in lucerne stems than in leaves with advanced phenology (Marten et al, 1988). Although differences in quality can be found between basal and apical portions of the stem throughout the growing season (Christian, Jones, & Freer, 1970), the quality of the stem as a whole organ is a matter of concern in the improvement of feeding value (Julier & Huyghe, 1997;Lenssen et al, 1991), given its large propor- This study confirmed earlier observations on the close relationship between environment DM yield and stem height in lucerne (Pembleton, Donaghy, Volenec, Smith, & Rawnsley, 2010;Volenec, Cherney, & Johnson, 1987) and the reduction in stem length and number of internodes caused by drought stress (Afsharmanesh, 2009;Sheaffer et al, 1998). The moisture-favourable Env3 exhibited the top values for stem length and forage yield.…”

Genetic engineering of grain and pasture legumes for improved nutritive value

“…The leaves of this perennial legume contain little lignified tissue; however, the older parts of the stems of the plant are highly lignified, and constitute a considerable proportion of the biomass of the crop (Christian, Jones & Freer, 1970). The biosynthesis of lignin in plants occurs via a pathway which is one of several branching from general phenylpropanoid metabolism, and most enzymes of this branch pathway have been identified (Fig.…”

Lucerne grazing management 2. Effect of grazing duration on defoliation pattern by ewes

“…The 20% decline in digestibility during a 12-day duration is consistent with the findings of Alder & Minson (1963) who measured a 7% decline following 1 day of grazing by steers. Most of this decline can be attributed to preferential selection of highly digestible parts by the sheep (Terry & Tilley 1964;Christian et al 1970) but may also be associated with a greater decline in levels of soluble carbohydrates in the stem over the longer grazing duration. There is a link between digestibility of stems and levels of soluble carbohydrate (Bailey et al 1970).…”