Anaerobic rumen fungi as a feed additive in ruminants: a review

The demand for meat and dairy products is increasing globally and to meet the growing demand for animal products, it is necessary to increase livestock productivity. The use of antibiotic growth promoters (AGPs) in livestock is banned in many countries which has led to lower feed efficiency issues and impaired growth rate. Recently, more emphasis has been given to the manipulation of the rumen ecosystem to enhance the utilization of feedstuff to improve production of ruminants by feeding direct-fed microbials (DFM). Ruminant diets are mostly composed of lignocellulosic feeds which can be breakdown by anaerobic rumen fungi (ARF) by penetrating the cell walls of plants through their rhizoids. ARF can be used as DFM to increase the digestibility of the fibrous feed and overall feed efficiency of the ruminants, thereby enhancing animal performance. For ruminants, ARF as DFM has been successfully used to improve fiber digestion in the rumen, feed efficiency, daily gain and milk production. ARF has applications as silage additives during the ensiling process for improving ensiling quality, preservation and rumen degradation. Recently, the use of novel silage additives such as ARF and their enzymes has been suggested to pre-cleave fibrous structures effectively in silages. The challenges in the application of ARF as feed additives are administration methods and large-scale cultivation. Further research is needed to develop economically feasible industrial-scale production of anaerobic fungal probiotics.