Alternative use of various plant parts of vachellia nilotica as fodder for small ruminants: implications for woody plant encroachment

Abstract

Woody plant encroachment is regard as a common problem in South African rangelands, however edible twigs and seed pods from these plants are generally regarded as an important source of protein to livestock during the dry season. Livestock, especially small ruminants feed more on the seed pods of these woody plant, which, in turn, results in the dispersal of scarified seeds back in the rangelands through their feces. This, in turn, results in further woody plant encroachment and bush thickening. The current study aimed to explore the use of Vachellia nilotica plant parts (seed pods and edible twigs) as fodder for small ruminants to fill the dry season feed shortage. To achieve this aim, the study examined the possibility of reducing the dispersal of viable seeds in rangelands and controlling bush encroachment by including Vachellia nilotica seeds into livestock feeds. The seed pods and edible shoots of Vachellia nilotica were harvested separately, and analyzed for mineral, protein and fibre contents at different seed pod inclusion rates, with or without the addition of feed additive. Based on the chemical analysis, six diets (1) 100% V. nilotica seed pods (un-chipped), 2) 100% V. nilotica seed pods (chipped), 3) 100% V. nilotica seed pods (un-chipped) + feed additive, 4) 100% V. nilotica seed pods (chipped) + feed additive, 5) 4:4 (V. nilotica shoots: V. nilotica chipped seed pods) and 6) 4:4 (V. nilotica shoots: V. nilotica chipped seed pods) + feed additive) were selected to feed 24 goats and measure the number of seeds that was recovered and germinated after ingestion. Results from the study showed significant differences (p < 0.05) with higher concentrations of CP, TDN, K, Mg, P and Zn in the 100% V. nilotica seed pods compared to the 100% V. nilotica shoots. Furthermore, a relatively high (p < 0.05) digestible dry matter (DDM), digestible organic matter (DOM), metabolizable energy (ME), net energy for lactation (NEL), and net energy for growth (NEG) were observed in the 100% V. nilotica seed pods, shoots + seed pods and 100% V. nilotica seed pods. The concentrations of N, P, K, and CP from the 100% shoots fodder significantly increased (p < 0.05) upon the addition of feed additives (i.e.Voermol LS33). The highest seed pod inclusion of 100% shoot fodder, the content level of DDM, TDN, DOM, ME, NEL, and NEG significantly increased (p < 0.05). No significant differences (p ≥ 0.05) were observed in mineral content between the 100% shoot and the shoots + seed pod fodders, irrespective of the seed pod inclusion levels. In the feeding trial, no differences (p ≥ 0.05) were observed in feeds consumed (58- 83%) and remained (17-35%) among the six experimental diets. However, seeds ingested were significantly higher (p < 0.05) when the seed pods were chipped, and this also influenced significantly (p < 0.05) the number of seed recovered in the diets compared to the control. Less than 2% of the chipped seed pods diet were recovered after ingestion, while 3% and 6% of seeds in the diets containing whole seed pods with or without Voermol LS33. The study found that chipping seed pods before incorporating them into livestock diets led to a significant decrease in the number of seeds recovered. Therefore, chipping the seed pods prior to adding to the shoot material in diets significantly reduces the number of seeds that could potentially be dispersed through endozoochory, thereby reducing bush encroachment. However, it should be taken into consideration that the majority of the 2% of seeds recovered were dormant but still viable. Another aim of the study was to explore the possibility of whether V. nilotica edible shoots (chipped) can be preserved in the form of silage. The ensiling lasted for 60 days, and fermentation characteristics, dry matter, mineral nutrients and aerobic stability were analysed within 4 treatments: 1) control (shoots only without molasses), 2) shoots + seed pods (without molasses), 3) shoots + molasses (without seed pods), and 4) shoots + molasses + seed pods. The study found that dry matter content of V. nilotica materials in all treatments significantly differ (p < 0.05) at ensiling, but they all fall within the recommended DM range of 45-55% for high DM legume silages. The same was true for CP (7-8%), ADF, NDF and ash content. Although significant differences were also observed in pH level between days and treatments, it was within the recommended level of 4.3-5.0. Therefore, results from this work show that all parameters measured fall within the recommended range of well-fermented and preserved legume silage. These findings demonstrate that V. nilotica can be effectively preserved as silage in the wet season in order to feed during dry season or to counter the feed shortage during dry season. However, more research is necessary to determine whether the addition of inoculants will likely affect the nutritional quality of the silage produced.