Masters Degrees (Forest and Wood Science)

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Browsing Masters Degrees (Forest and Wood Science) by Subject "Agriculture -- Effect of environment on -- Namibia"

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    Utilization preparation of Senegalia mellifera to produce animal fodder
    (Stellenbosch : Stellenbosch University, 2023-03) Neethling, Alwyn; Tyhoda, Luvuyo; Gorgens, Johann F. ; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
    ENGLISH ABSTRACT: Senegalia mellifera, a tree species associated with significant bush encroachment, has been noted to cause great harm to the environment, the agricultural sector and inevitably the greater economy in Namibia. This is due to Namibia having one of the most severe cases of bush encroachment caused by Senegalia mellifera, which occupies about 70% of all arable land. The severe loss in arable land causes a reduction in available grazing for livestock. Furthermore, clearing these encroached areas could increase available grazing areas for livestock. In addition, due to droughts occurring in Namibia, farmers struggle to keep livestock alive and tend to reduce the number of livestock on their farms. As these droughts intensify, animal feed prices increase, making it unaffordable. Thus, by de-bushing encroached areas and making use of Senegalia mellifera to produce animal fodder, one could aid farms in keeping livestock alive during droughts, while addressing a significant ecological, environmental and biodiversity threat. Furthermore, in the event of animal feed being produced from Senegalia mellifera, farmers tend to only use the small, nutritious branches. By making use of these branches, the farms produce a form of feed that requires additives and they do not solve the problem of bush encroachment caused by Senegalia mellifera. Thus, by harvesting and utilising the complete tree for animal-fodder, one could establish whether the nutritional characteristics are influenced when proportions of stem material are added, and how various pre-treatment methods could overall affect the material digestibility. The objectives of the study were to: (1) evaluate the chemical composition and nutritional characteristics of a mixture of Senegalia mellifera wood that consisted of twigs leaves and mature stems; (2) comparatively study the use of different pre-treatment methods, namely steam explosion (160-220°C, 2-10 min), alkaline catalysed steam explosion (160-220°C, 2-10 min, 1-7 wt.% NaOH) and aqueous ammonia soaking (60-120°C, 1-6 hours, 5-15 wt.% NH3) to increase the material digestibility and available metabolizable energy of Senegalia mellifera. The chemical compositional analysis of Senegalia mellifera raw material indicated a high concentration of lignin (32.06 ± 0.054 %DM) and low levels of cellulose (27.19 ± 0.094 %DM). Nutritional analysis indicated a low level of crude protein (CP) (4.9 ± 1 %DM) in the animal feed mixture. Finally, the feed also had a low digestibility (EDOM) (50.02 g/kg DM) and available metabolizable energy (0.46 MJ/kg DM MEEDOM & 1.32 MJ/kg DM NviroTek), which can be attributed to a high degree of lignification and cellulose crystallinity. After the raw material had been pre-treated, a significant improvement (p < 0.05) on material digestibility and available metabolizable energy was observed in all samples. The effectiveness of the individual treatments in terms of material digestibility was as follows: The most effective method was alkaline catalysed steam explosion, followed by the auto catalytic steam explosion, and the least effective method was aqueous ammonia soaking. Alkaline catalysed steam explosion had the most significant influence on material digestibility by improving it 11-fold to 580.30 g/kg DM (58 %DM) and increasing the available metabolizable energy by just over 15 times to a maximum of 7.19 MJ/kg DM in the most severe conditions (220°C, 10 min, 7 wt.% NaOH). Auto catalytic steam explosion also increased the material digestibility 5-fold to 254.7 g/kg DM (25.47 %DM), while increasing the available metabolic energy (7.8-fold) to 3.59 MJ/kg DM in treatment condition (220°C, 2 min). Finally, the use of aqueous ammonia soaking was the least effective method as it only increased the digestibility twice and the metabolizable energy was increased almost 4-fold to 138.1 g/kg DM (13.81%DM) and 1.79 MJ/kg DM in the most severe treatment conditions (120°C, 6 hours, 15 wt.% NH3).One of the major concerns regarding proper rumen microbial function is the requirement of crude protein (CP). It was thus important to track this key nutritional factor throughout the pre-treatment process. Aqueous ammonia soaking was the most effective in preserving the crude protein content, followed by auto catalytic steam explosion, and the least effective method was alkaline catalysed steam explosion. Regarding the nutritional characteristics, it was observed that even though alkaline catalysed steam explosion improved material degradability and available energy, the already low level of CP was sacrificed, reducing it to 1.05 %DM, which is significantly lower (p < 0.05) when compared to the CP preservation by auto catalytic steam explosion and aqueous ammonia soaking. Finally, regarding crude protein, aqueous ammonia soaking increased the CP and the available nitrogen in fodder by 13.5-282.78 g/kg DM (1.35-28.28 %DM) due to the chemical binding of nitrogen to the prepared feed. This can be a possible reason for a false negative regarding the increase in crude protein noted during aqueous ammonia soaking. In conclusion, by comparing the in vitro enzymatic digestibility, the overall available metabolised energy and available crude protein of three different means of pre-treatment, this study showed that alkaline catalysed steam explosion provided the best overall increase in the digestibility of Senegalia mellifera and thus increased the available metabolic energy for ruminants, even though the crude protein fraction was sacrificed in the pre-treatment process. Regarding animal feed, it is plausible that the removal of a Senegalia mellifera as a whole bush consisting out of stem branches and leaves could be used as an animal feed after the optimal ACS pre-treatment.