Fungal treatment of selected matured forages to improve their value for ruminant feeding

Abstract

Ruminant nutritionists have been faced with a lot of challenges in improving the digestibility of low quality feeds that are available for ruminants in the dry season in most tropical regions. In view of this, they are interested in finding low cost approaches that are not hazardous to the animals, people and the environment. The use of biological methods (i.e. microbes) has been found to be capable of breaking down the structural components of these feeds such that the animals can access the energy components of the feeds. Among these microbes fungi have been found to be more efficient in degrading the structural components due to their enzymatic activity. Therefore, a series of experiments was carried out to evaluate the effectiveness of both aerobic and anaerobic fungi in improving some of the most available and abundant forages in Nigeria alongside two commonly used British forages. The aerobic experiment using CR (C. rivulosus) and PO (P. ostreatus) was conducted to improve the nutritive value of selected matured forages (A. gayanus, B. decumbens, and T. aestivum) along with L. perenne that was used as a benchmark by degrading lignin. However, there are several reports where fungal treatment does not improve the nutritive value of forages. This research, therefore, investigated one possible reason that may have caused this, which is the removal of solubles caused by improper handling of pre-treated forages on the farm using PFF (pump filtered method; representing the use of heavy stones on sacks) and FFF (free filtered method; representing the use of porous sacks). These 2 methods were applied on the selected forages after pre-treatment was carried out using two substrate-liquid ratios (1:3 & 1:5) and incubated at 200C (CR) and 250C (PO) for 14 days and 28 days respectively. The use of both methods resulted in soluble losses in the fungal pre-treated forages but more loss was obtained through the PFF method. The PFF method did negatively influence the ability of the fungi to improve the chemical composition of the pre-treated forages in comparison with the FFF method. Also, the PFF method did not improve the in vitro nutrient degradability and in vitro fermentation parameters of the fungal-pre-treated forages.. Farmers should endeavour to ensure that losses of solubles are minimal and consistent by using containers/bags/sacks that will not allow the escape of solubles during pre-treatment, and also ensure that no pressure is exerted on the pre-treated forages. The use of growth conditions favouring excessive growth and ligninolytic function by the fungi on the substrate should be avoided when implementing the upgrading of forages on the farm, as this leads to the release of more solubles that might be subsequently utilised by the fungi or lost through improper handling. The anaerobic experiment using (Neocallimastix and Opinomyces) was conducted to improve the nutrient utilisation of the selected matured forages when used as feed additives. These fungi were used as silage inoculants for the selected matured forages over 2 inoculation times (i.e. 14 and 28 days). The supplementation of these two anaerobic rumen fungi as silage inoculants improved the silage quality of the forages. This improvement was reflected in the reduced pH, increased CP content, decreased fibre content, increased metabolite contents especially by Orpninomyces sp., and increased TAN contents especially by Neocallimastix sp. This improvement was complemented with a minimal nutrient loss. Orpinomyces sp. had a greater preference in degrading fibre in the temperate forage silages, i.e. L. perenne silage and T. aestivum silage, while Neocallimastix sp. had a greater preference in degrading fibre in the tropical forage silages, i.e. A. gayanus silage and B. decumbens silage. Although the silage was improved, the fibre content was still high, but there is the possibility that the chemical bonds that exist between lignin and other polysaccharides might have been loosened during ensiling. These ensiled forages, therefore, require further degradation by rumen microbes for the utilisation of nutrients by ruminant animals