Sheep production on second generation, hardseeded annual pasture legumes fed as grazed and conserved forages in the Mediterranean-temperate environment of southern NSW

Lucinda Watt

    Research output: ThesisDoctoral Thesis

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    A second generation of annual legumes were developed with traits enabling them to grow in variable and adverse climatic and soil conditions compared to traditional subterranean clover (Trifolium subterraneum L.; annual) and lucerne (Medicago sativa L.; perennial) pastures. Agronomic studies have highlighted their suitability in pasture-crop rotations in addition to high biomass production and quality, which is advantageous for livestock production systems. However, few studies have investigated livestock production from these species. The value of second generation annual legumes arrowleaf clover (T. vesiculosum Savi), biserrula (Biserrula pelecinus L.), bladder clover (T. spumosum L.) and French serradella (Ornithopus sativus Brot) to livestock systems was investigated as: (1) grazed monoculture pastures and legume + oat swards; and (2) conserved forages. A series of experiments undertaken at Wagga Wagga, NSW evaluated growth rates and/or wool growth and incidence of health disorders of sheep consuming these species under similar growing and/or feeding conditions. In addition, nutrient digestibility and ruminal parameters of sheep fed these legumes were assessed. Dietary composition estimates were determined in lambs grazing legume + oat swards. A laboratory-based study was used to determine the dry matter (DM) and crude protein (CP) degradability of the legumes. As monoculture pastures, herbage biomass of arrowleaf clover (cv. Arrotas) became limiting (< 700 kg DM/ha) in late-winter early spring after 840 total grazing days/ha. Yet, in spring, herbage biomass was sufficient (> 2500 kg DM/ha) to support lamb growth (up to 323 g/d) over 1914 total grazing days/ha. Biserrula and bladder clover produced sufficient biomass for lamb growth in both late winter-spring (> 1972 kg DM/ha) and spring (> 2519 kg DM/ha). In late winter-early spring, total grazing days/ha were higher for lucerne and mixed lucerne + phalaris pastures (1170 grazing days/ha) than the annual legume pastures (811-990 grazing days/ha). Oversowing oats in regenerating arrowleaf clover, biserrula, bladder clover or French serradella pastures increased biomass in the winter (2225-4579 kg DM/ha) but oats dominated the swards. In late winter-early spring, second generation annual legumes had similar or higher digestible organic matter digestibility (DOMD; 71-78%) than lucerne (72%). In spring, the annual legume pastures differed in nutritive value due to varying stages of plant maturity. Earlier maturing bladder clover had lower DOMD (68%) and CP content (19%) than the other legume pastures (73-77% and 23-31%, respectively) due to senescence. The quality of biserrula declined during this period due to increasing maturity, although was similar to lucerne; however, lucerne was more responsive to late spring rainfall, increasing significantly in nutritive value. Arrowleaf clover maintained higher DOMD (77%) throughout spring. In winter, annual legume + oat swards had higher DOMD (76-77%) than lucerne + oat sward (71%), although sampling for the analysis of nutritive value was most likely biased by the higher biomass of barley grass in the sward. In all grazing experiments, the CP content of legume pastures and legume + oat swards generally met or exceeded the requirements for growing lambs (CP > 15%). In spring, rumen fermentation patterns in lambs grazing biserrula favoured the propionic acid pathway; however, this did not appear to influence lamb growth as average daily LW change of lambs grazing the annual legume or lucerne pastures (147-187 g/d) was similar. Lambs grazing lucerne + phalaris grew less (103 g/d) than those grazing arrowleaf clover (187 g/d) or bladder clover (176 g/d) pastures. In late winter-early spring, arrowleaf clover supported lower total animal production/ha (83 kg LW gain/ha) than the other pastures. In spring, biserrula and bladder clover were managed for seed set resulting in lower total animal production/ha (105 kg LW gain/ha and 128 kg LW gain/ha, respectively) compared to arrowleaf clover (176 kg LW gain/ha). In winter, the annual legume + oat and lucerne + oat swards supported similar average daily LW change (ADG; 105-139 g/d) and total animal production/ha (157-264 kg LW gain/ha), but ADG was lower than predicted that was likely due to high rainfall and waterlogging and high moisture content (< 16% DM) of the legume + oat swards affecting intakes. Animals grazing biserrula may develop primary photosensitisation or an aversion to the plant leading to reduced DM intake (DMI) or greater selection of other species when grazed in mixed swards (86% oats vs 14% biserrula diet composition). Lambs grazing biserrula + oat swards increased their selectivity for biserrula (60% diet composition) after a period of grazing; although, the reasons for this are unclear. Oversowing oats into biserrula pastures may help mitigate primary photosensitisation. Penned lambs fed fresh arrowleaf clover developed frothy bloat (100% incidence), which is the first known documented case. Immediately soluble and potentially degradable CP of arrowleaf clover pasture did not appear to be contributing factors, but warrant further investigation. As conserved forage, bladder clover hay had higher DM digestibility (73%) than arrowleaf clover, subterranean clover and lower quality lucerne + oat hays (68%, 65% and 56%, respectively). The DMI/kg LW and ADG of lambs fed bladder clover hay (34 g/kg LW.d and 248 g/d, respectively) were higher than those fed subterranean clover or lucerne + oat hay (30-31 g/kg LW.d and 182-188 g/d, respectively). Lambs fed arrowleaf clover hay had similar DMI and ADG (204 g/d) to those fed the other hays. In a separate study, lambs fed biserrula, biserrula + wheat + field pea or wheat + field pea silages did not gain LW over a 49 d feeding period. The ADG and DMI of the lambs fed the silages was lower than predicted, which may have been due to poor fermentation quality or mould contamination of the silages. However, maintenance level DMI did maintain lamb LW. Strategically utilising second generation and traditional legumes in a whole farm system offers opportunity to improve total on-farm feed supply. Furthermore, their use as conserved forages enables utilisation of excess biomass during seasonal feed gaps. This information may assist producers in making informed decisions about the inclusion of these species in their farming systems for more sustainable and productive livestock and/or mixed farming enterprises in southern NSW.
    Original languageEnglish
    QualificationDoctor of Philosophy
    Awarding Institution
    • Charles Sturt University
    • Friend, Michael, Principal Supervisor
    • Krebs, Gaye, Advisor
    • Piltz, John, Advisor
    • Hackney, Belinda, Advisor
    Place of PublicationAustralia
    Publication statusPublished - 2019


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