1 Antinutrients in Ruminant Feeds: A review Isiaka O. Olarinre, Mohammed A. Al-Badwi and Mutassim M. Abdelrahman* Department of Animal Production, Faculty of Food and Agriculture Sciences, King Saud University, P.O. Box 2460, Riyadh 11451, Saudi Arabia *Corresponding author: mutassimm@yahoo.com Abstract: The current challenges in ruminant production are the development of strategies to reduce the cost of feeding, improve the quality of products as well as mitigate the negative impact of production on the environment. Plant-based feeds are chiefly available for animals and may be used to reduce the cost of feeding. However, the presence of toxic substances known as antinutrients limits their full utilization in livestock industries. They are present in different feeds of energy and protein sources. The antinutrients such as saponins, cyanogenic glycosides, goitrogen, lectin, phytoestrogen, oxalate, protease inhibitors, trypsin inhibitors, alkaloids, mimosine, and phytates are harmful to animals when consumed in large quantities. They have unpalatable effects on the digestive system, as well as the overall production performance and welfare of the animals. The exact effects of antinutrients on ruminant gut microbiota and microbiome have not been adequately reported. However, different strategies to enhance the bioavailable nutrients such as milling, soaking, steaming, fermentation, germination, autoclaving, and the use of supplements have been established to improve the quality of plant-based feed and to ameliorate their disastrous effects on the overall quantity and quality of production characterizing of animals. [Isiaka O. Olarinre, Mohammed A. Al-Badwi and Mutassim M. Abdelrahman. Antinutrients in Ruminant Feeds: A review. Researcher 2022;14(4):1-8] ISSN 1553-9865 (print); ISSN 2163-8950 (online). http://www.sciencepub.net/researcher . 1. doi:10.7537/marsrsj140422.01. Keywords: Antinutrients, food bioavailable, phytoestrogen, gut microbiome, ruminants. Introduction The importance of nutrition in livestock enterprise has been fully documented as nutrition gulps about 70% of production. The current challenges in ruminant production are the development of strategies to reduce the cost of feeding, improve the quality of products as well as mitigate the negative impact of production on the environment (Yacout, 2016). Feeds of plant origin are chiefly available in many developing countries for animal utilization (Le Houérou, 2000). Yacout (2016) reported that the use of plant-based feeds may subsidize feeding costs and eco-friendly influence. However, as good as plant-based feeds are, the presence of antinutrients impaired their full utilization by animals, and this deficiency is a great concern of many researchers as well as livestock industries globally (Yacout, 2016). Silage, hay, and green fodder contain vital nutrients, but the presence of some toxic materials or incriminating factors reduce their full utilization (Ramteke et al., 2019b). Some antinutrients also affect animal performance. Phytoestrogen or lignin components of sunflower have been reported to have negative effects on the reproductive qualities of ewes (Alharthi et al., 2021). These toxic materials (antinutrients) are also referred to as allelochemicals (Kumar, 1992). Recently, the deleterious effects of antinutrients on the gut microbiota of Homo sapiens and animals have started gaining momentum. Antinutrients are organic or synthetic substances that either by themselves or via their metabolic products block the absorption and utilization of nutrients (Akande et al., 2010; Yacout, 2016). They are found mostly in plants of energy and protein sources and have negative effects on the overall well- being as well as the productive performance of the farm animals (Epafras and reas, 2019). Many of these compounds are present virtually in every plant that is used in practical feeding (D’mello, 2000). Several reviews have been based on general antinutrients as well as general strategies to reduce their harmful effects in ruminant feeding, to the best of our knowledge, highly perilous anti-nutrients, as well as their effects on the digestive system, reproductive system, and gut microbiota of ruminants, have not been properly documented. Therefore, the objective of this review is to elucidate some toxic dangerous antinutrients, specific economic treatment strategies, their effects on nutrient utilization, digestive and reproductive performance as well as the well-being of the gut microbiota of ruminants.