Browsing by Author "Charamba, Vonai"

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    A hierarchical non-parametric Bayesian testlet model for dual local dependence
    (University of Namibia, 2021) Charamba, Vonai; Kazembe, Lawrence
    The use of psychometric tests to measure the level of individuals on unobservable traits is common in many fields and item response theory (IRT) models are usually used for proficiency measurement. Standard IRT models assume local person and item independence and normality assumption for the true ability distribution. However, respondents are often clustered and test items are often grouped according to sub-content measuring the same stimuli or sub-component of the trait. This study presents a non-parametric polytomous multilevel testlet model for simultaneously modelling person and item clustering effects. The grouping variable is assumed unknown and determined from the data using the Dirichlet Process. The model was compared with a parametric dual model with groups assumed to be known, the testlet model, the Generalised Partial Credit Model and the multilevel model accounting for person dependence effects only in terms of systematic, random and total errors in person and item parameter estimation and test information and reliability, for simulated and real life data. The effects of ignoring dual dependence effects were evaluated for variant group, sample, testlet size, number of response options and mixed items tests. Groups of size 5, 20 and 40 were compared for 400, 1000 and 2000 respondents. The effects of ignoring dependence effects were compared for 6 testlets of 3, 6 and 10 items each for 3, 4 and 5 response categories were compared. Consequences of mis-specifying the slope and proficiency distributional parameters were evaluated where the competing models estimated item and person parameters for skewed, bimodal, normal and uniformly distributed traits and constant and stochastic slopes. Three dependency conditions (0, xi none; 0.5, medium; 1, large), were considered for both local item dependency (LID) and local person dependency (LPD). For each simulation study, a fully-crossed factorial design was employed and the general linear model was employed for comparing estimation errors. Significant different means were detected by use of Cohen’s effect size, f. In general, ignoring LPD effects resulted in increased bias and total errors in the estimation of ability parameters while ignorance of LID negatively impacted on item parameter estimation increasing with sample size, testlet size and number of options. Failure to account for LID resulted in underestimation of proficiency standard errors, thus resulting in overestimation of test information and reliability. When dual dependence effects were ignored, both item and ability parameter estimation accuracy was reduced. The non-parameter model detected the number of groups and group membership well especially for smaller groups, increasingly with sample size, testlet size and number of categories. However, the non-parametric models requires high computational performance Considering the consequences of ignoring random effects and the computation efficiency required by the non-parametric model, it is recommended that the model be used to detect dependence effects and groups, and standard IRT models be applied for independent persons
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    Climate change adaptation strategies among smallholder livestock farmers in Namibia's Omaheke Region, Namibia
    (Discover Sustainability, 2025) Siririka, Ndjipua Avihe Tjaondjo; Charamba, Vonai; Mupangwa, Johnfisher; Shipandeni, Maria N. T.; Kahumba, Absalom
    The challenges of climate change are continuously increasing, constituting a major threat to livestock production, which is more than a socio-economic cornerstone in Namibian rural communal farmers, contributing approximately two-thirds of the country’s agricultural GDP. Climate variability, which may be in the form of drought, very high temperatures, floods and frosts has been reported to have detrimental effects on feed and water availability, leading to reduced livestock weight, growth, production and reproductive performance, and ultimately high mortality. Understanding smallholder farmers’ socio-psychological antecedents such as knowledge, attitudes and perceptions and the way they influence their level of adaptation to CC mitigation strategies needs to be assessed, as it guides CC policy formulation and intervention programmes. The study investigated CC perception and adaptation strategies for livestock farmers in Omaheke Region. Data were gathered from (n=80) purposively sampled farmers in Epukiro and Otjombinde constituencies based on livestock ownership. The study revealed that 93.8% of the respondents were aware that the climate is changing, with attributes such as very high and very low temperatures, high and low rainfall, and drought having been noticed. Climate change has been attributed to both human and natural activity. The study observed that the implementation of CC adaptation strategies in livestock agriculture is low, thus recommends that the improvement of adaptation techniques involving employing extension services, promotion of farmer-to-farmer extension, and utilization of various information sources of climate knowledge, such as farmers’ associations and social organizations, should be the future policy priority
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    Effects of feeding incremental levels of Spirulina platensis on feed intake and growth performance of Boschveld and Potchefstroom Koekoek chicken breeds
    (Discover Agriculture, 2024) Nambahu, Aino; Petrus, Ndiilokelwa Patricia; Mupangwa, Johnfisher; Charamba, Vonai; Lutaaya, Emmanuel
    spirulina is increasingly being used in feed manufacturing because of its high nutritional value, especially proteins, for humans and animals. This study examined the feed intake and growth performance of Boschveld and Potchefstroom Koekoek chicken breeds when soybean meal was substituted with incremental levels of Spirulina platensis. The experimental design was a 2×4 factorial with repeated measures over a 12-week period, with breed and diet as factors. The experimental unit was a cage holding 3 birds, with 3 cages allocated to each breed-diet combination, hence 36 birds per breed. The diets were: 0%, 5%, 10% and 15% using dried Spirulina platensis powder to replace soybean meal per 100 kg of feed. Chickens fed control diet consumed more (P<0.05) feed than those fed Spirulina-containing diets. Diet affected (P<0.0001) final weights (g) of the birds which were 1093.2, 921.6, 762.8 and 771.2 for 0%, 5%, 10% and 15% inclusion levels of Spirulina platensis, respectively. Boschveld chickens had better average daily gain compared to Potchefstroom Koekoek at week 15–16. Averaged over the 12 weeks, the control diet gave better (P<0.0001) average daily gain (9.42 g/d) than the Spirulina-containing diets. Over the 12 weeks, the control diet had a more desirable (7.79 vs. 8.17, P=0.01) feed conversion ratio than the Spirulina-containing diets Spirulina at a level of 5–10% can be used as a protein supplement in indigenous chicken feeds because it resulted in growth performance close to control diets
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    Evaluation of factors affecting productivity and profitability of Lohmann Brown layers in a semi-arid environment
    (2020) Samkange, Alaster; Kandiwa, Erick; Mushonga, Borden; Amunyela, Selma A.; Bishi, Alec S.; Charamba, Vonai; Mbiri, Pricilla
    A prospective 27-week study investigated the effect of age, ambient temperature, humidity and photoperiod on egg weight and production in Lohmann Brown layers, and thus the profitability of the egg-producing enterprise at a farm in central Namibia, designated Farm A. Overall, age of birds, average temperature, humidity and photoperiod were strongly correlated with mean egg weight (r=0.84, 0.7, -0.51 and 0.7, respectively; p<0.001) but there was a weaker correlation of age, temperature, humidity and photoperiod to the number of eggs/bird (r=0.49, 0.41, -0.43 and 0.34, respectively). Increase in the age of birds, temperature and photoperiod resulted in a significant increase in mean egg weight. A decrease in humidity, however, resulted in a significant increase in mean egg weight. Labour and feed costs contributed 51% and 14%, respectively, to the overall costs of the enterprise. Egg sales contributed the bulk of the income at 88%, which was followed by the sale of spent layers at 12%.The study concluded that Lohmann Brown layers performed well in the semi-arid conditions of central Namibia provided that extreme environmental conditions are avoided. The high input costs, especially labour and feed, were the main constraints to profitability and finding ways to reducing these costs is key to increasing profitability. Increasing the size of the flock is one practical way of offsetting the high labour costs.
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    Indigenous knowledge of browse species and nutritional quality of dominant indigenous browse species in the Kavango West Region of Namibia
    (Discover Sustainability, 2024) Hamukwaya, Rosa N.; Charamba, Vonai; Kahumba, Absalom; Shipandeni, Maria N. T.; Mupangwa, Johnfisher
    Livestock production is crucial to the livelihoods of rural Namibians but highly constrained by feed shortages due to climate change and bush encroachment. The study investigated the grazing and feeding practices and indigenous knowledge of browsable and non-browsable species by interviewing 30 small-scale farmers in the Kavango West Region. It assessed the nutritive value for the three most commonly identified browsable species. The study observed that livestock relies on communal rangeland, roadside, and riverside grazing, with supplements from crop residues during the dry seasons. However, most farmers experience feed shortages mainly in the dry season, which results in decreased livestock productivity. Farmers are knowledgeable on browsable and non-browsable woody species in their locality, but most do not harvest pods, leaves and twigs to supplement their animals in the dry season, citing labour shortage, and they are not aware that the bush species resources can be harvested and be used during seasons when feed resources are scarce. The nutritive value analysis indicated that there is a need for strategic supplementation of the browsable species for them to be effectively utilised as livestock feed, thus farmers must be capacitated on when and how to utilise these species when herbaceous pasture grasses and legumes are senescent as well as how to harvest forage alongside rivers and roads for stall feeding to avoid accidents. Our findings will be important for policy formulation in trying to come up with better ways of mitigating the consequences of climate change
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    Quantification and characterization of nutrients in Senegalia mellifera milled biomass, feed intake and nitrogen balance in female Boer goats fed with Senegalia mellifera bush-based feeds
    (International Journal of Agricultural Research and Review, 2024) Epafras, A.; Mupangwa, Johnfisher; Charamba, Vonai; De la Puerta, M. L. F.
    The objectives of this study were to quantify and characterise the nutritional content of milled Senegalia mellifera milled biomass obtained from nine blocks at Neudamm Farm and to determine the dry matter intake (DMI), apparent digestibility and nitrogen retention in female Boer goats fed with Senegalia mellifera bush based feeds. Wood ash (WA), polyethylene glycol (PEG, 6 000) and biochar were evaluated as tannin deactivation methods. The milled biomass of S. mellifera was mixed using a clean concrete mixer with the following ingredients: yellow maize meal, liquid molasses; Marula oil press cake and coarse salt to formulate a complete diet with 14% CP and 11MJ ME/kg. Detannification treatment methods were added at a level of 5 g per day during feeding time. We used eight (8) female Boer goats weighing an average of 31.5 kg (± 2.5 kg) for the feeding experiment. We penned the goats individually in metabolic cages. Clean water was available ad libitum to the goats during the entire feeding experiment. The goats were fed in a 4x4 cross over Latin square design with four periods of experimental feeding. Each period lasted for 17 days, resulting in 68 days of experimental feeding. The goats were fed twice daily at 09:00h and 16:00h. The level of dry matter (DM) of feed offered was 4% of body weight. The results obtained in this study showed that there was a significant difference (p <0.05) in the chemical composition of Senegalia mellifera milled biomass harvested from the nine blocks at Neudamm Farm. The CP content of Senegalia mellifera milled biomass ranged from 9.39 to 9.68 %DM while the NDF and ADF ranged from 59.17 to 64.33%DM and 43.77 to 48.01%DM, respectively. The condensed tannins (CT) content from all blocks did not differ (p >0.05) and had a mean of 0.02 to 0.03%DM as leucocyanidin equivalent (LE Absorbance at 550 nm). The apparent digestibility coefficients of DM, OM and NDF were not significantly different among treatments and the control diet (p >0.05). Goats fed biochar treated diet had the highest nitrogen intake of 13.74g/d (p <0.05), faecal nitrogen of 8.43g/d (p <0.05) and nitrogen retention of 5.11g/d (p <0.05), while goats fed the control feed (CNT), PEG and WA were similar (p >0.05). All treatments resulted in a positive nitrogen retention (p >0.05) with mean values ranging from 3.79 to 5.11 g/d. The study concluded that, there was a significant difference (p <0.05) in the chemical composition of S. mellifera milled biomass collected from nine blocks at Neudamm Farm. Given the high CP content of the S. mellifera, this fodder resource can be considered a suitable supplement for poor quality (low N content) natural pastures and crop residues such as grass hay, straw and stover. The study also concluded that, there was a significant difference (p <0.05) in the DMI, and nitrogen balance in Boer goats fed with A. mellifera feeds treated with Wood ash (WA), Polyethylene glycol (PEG, 6 000) and Biochar (BIO). The study therefore recommends that each detannification method should be tested at different rates of inclusion in S. mellifera bush based feed resources
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    Relative importance analysis of the factors influencing maize productivity at Olushandja and Etunda irrigation Schemes of Namibia: A secondary analysis of data from farm household survey
    (University of Namibia, 2017) Charamba, Vonai; Thomas, Benisiu; Charamba, Beatrice
    The main objective of this study was to apply relative importance analysis to determine the main factors that affect maize productivity for smallholder maize farmers in the Olushandja Dam and Etunda Irrigation Schemes, north-central Namibia. According to the analysis the key determinants were labour, consultation with extension service providers, land under maize production, the type of seeds used (local or hybrid), access to credit facilities, the experience in horticultural farming. The results singled out labour as the most important factor in maize production, accounting for 16.4% of the farm level variations in technical efficiencies. Technical efficiency gains as the size of land increases. This probably means that those farmers with small plots applied too much of inputs with respect to the size of their land. Farmers who consult extension services and those trained in good horticultural practices were more technically efficient and credit facilities should be availed to farmers so that they can access farm inputs in time to boost productivity.
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    Utilising encroacher bush in animal feeding
    (Springer, 2023) Mupangwa, Johnfisher; Lutaaya, Emmanuel; Shipandeni, Maria Ndakula Tautiko; Kahumba, Absalom; Charamba, Vonai; Shiningavamwe, Katrina Lugambo
    Livestock production is a major economic and livelihood activity in Namibia which contributes at least 75% to total agricultural output. The industry faces challenges including prolonged droughts, increased production costs, bush encroachment, variable climatic conditions and disease outbreaks. Bush encroachment and prolonged drought spells pose a major concern as they result in reduced carrying capacity of rangelands. The encroacher woody browse plants are potential animal feeds as they provide considerable amount of biomass from leaves and small twigs as well as pods that provide nutrients to ruminant livestock during the long dry season. Converting the biomass from the encroacher bushes into livestock fodder is one best management practice of controlling bush encroachment while increasing the availability of ruminant feeds sustainably without competing with human food production. Our chapter provides data on the nutritional content of encroacher bushes in different seasons and feeding value of bush-based feeds as an alternative feed resource for ruminant livestock. The chapter presents the opportunity and evidence that shows that utilising encroacher bush-based feeds in ruminant livestock feeding results in animal growth and the production of quality carcasses that contribute to human protein food. We conclude that the utilisation of rangeland encroacher bush species in sub-Saharan Africa in bush-based feeds provides sufficient nutrients to support improved ruminant livestock production and contributes to rangeland ecosystems restoration