Population growth and the enrichment of many countries are increasing the demand for increased livestock production and quality products [1]. Worldwide meat production has increased from 317 million metric tons to approximately 350.5 million metric tons from 2016 to 2023 [2] and is forecasted to marginally increase to a further 364 million tons [3]. This was accompanied by an increase in demand for higher-quality products ^[4][5][4,5]. Beef and veal have the third largest production volume, behind poultry and pork and ahead of sheep [6]. However, beef production represents a complex global sustainability challenge, including the need to meet the increasing demand and the need to respond to climate change and/or environmental footprints. Of all agricultural products, beef production requires the most land and water, and its production contributes the highest amount of greenhouse gas (GHG) emissions. Thus, the consumption of beef continues to pose several threats to the environment. On the other hand, the ability to predict the sensory and nutritional properties of meat according to production factors has become a major objective of the supply chain [7]. This evokes a need for sustainable beef production with the exploration of novel feed resources that will provide mitigation strategies for environmental impacts while not compromising beef quality.

The feasibility of using alternative feeds for ruminants depends, among other things, on the feed value of novel feeds, animal production responses, and feed costs compared to conventional feeds [8]. Several feed resources which include crop residues, Agro-industrial by-products, and non-conventional feedstuffs are already in use, but some of the constraints limiting the efficient utilization of these feed resources include low nutritive content, their conservation is challenging, some have antinutritional components, production often seasonal, and processing may be difficult.

A novel or under-explored feed additive like fossil shell flour (FSF) has the potential to supplement traditional crops in beef cattle rations, responding to environmental footprints while providing sustainable production and not compromising product quality [9]. Fossil shell flour, commonly known as diatomaceous earth (DE) is the remains of microscopic single-celled plants (Phytoplankton) called diatoms found in oceans and lakes in many parts of the world [9]. These remains have long been mined from underwater beds or ancient dried lake bottoms for decades and have numerous industrial applications.

Diatomaceous earth is mined, milled, and processed into various types for several uses. There are two main types of diatomaceous earth: food grade and filter/non-food grade [9]. Unlike the filter grade, the food-grade DE is commonly used in agricultural and food industries since it is considered safe for both humans and animals ^[9][10][9,10]. Fossil shell flour is non-toxic, cheap, and readily available in huge quantities in many countries [9]. This makes affordability and availability two of the greatest advantages of FSF for its use by any farmer [9]. In livestock production, FSF has recently been modified as an additive for several uses. It has been used as a feed additive, growth promoter, mycotoxin binder, water purifier, vaccine adjuvant, in inert dust applications in stored-pest management, a pesticide, and a natural source of silicon and anthelmintic [9]. Although FSF is beginning to gain interest in livestock production, more so in sheep, broilers, and layers, the use of FSF in cattle production remains unexplored.

2. Fossil Shell Flour as a Feed Additive

The quality, flavor, and composition of beef change with the composition of the cattle’s diet [11]. The plane of nutrition has been found to influence meat quality due to its regulatory effect on the biological processes in muscle and in fat deposition ^[12][13][14][12,13,14]. Likewise, the type of forage fed to cattle affects both the carcass and meat quality characteristics of beef. Thus, recently beef quality including its fatty acid composition has been the focus of interest of many customers and researchers [15]. In most tropical countries, livestock is mainly reared under extensive production systems, where they mostly depend on natural pastures for their nutrients [16]. This type of production has the disadvantage of the scarcity of forage during the dry season, resulting in animals consuming a greater quantity of low-quality forage [17] and less palatable species resulting in an approximately 50% reduction in live weight gained during the wet season [18]. Likewise, feedlot cattle are also affected by climate change through impacts on forage and crop-based feeds. As a result, several feed additives have been used to supplement poor-quality feeds for livestock. These include antibiotics, probiotics, prebiotics, enzymes, antioxidants, mycotoxin binders, organic acids, beta-agonists, hormones, defaunation agents, herbal feed additives, and essential oils, which are mostly chemical-based [19]. It has, however, been indicated that, because of their chemical and physical characteristics, some of these feed additives could decrease feed intake due to a decline in liking and appetite of the consumed feed ^[20][21][20,21]. Also, recently, the use of these chemical-based feed additives has created concerns about chemical residues in meat and other animal products ^[22][23][22,23]. There is also an alarming ecological risk that is increasing with the accumulation of veterinary antibiotic residue in animal manure [24]. Due to the possible risks of chemical-based feed additives, there has been a rising interest in natural growth promoters (NGPs). Production systems have their interest inclined toward various plants and plant extracts, enzymes, organic acids, and oils as possible NGPs that are eco-friendly [25]. However, one of the major constraints in using these NGPs is the time and cost involved in their harvesting [9]. Nonetheless, one NGP that could substitute chemical-based feed additives, boost feed intake, and be useful as a cost-effective, readily available, healthy, and eco-friendly feed additive is fossil shell flour. Fossil shell flour is a natural, organic, silicon-rich substance that occurs as a soft sedimentary rock made up of fossilized relics of diatoms. It has important physical and chemical characteristics enabling its use as a feed additive, with mineral constituents that include Copper (30 mg/kg), Sodium (923 mg/kg), Zinc (118 mg/kg), Iron (79.55 mg/kg), Boron, 23 mg/kg, Magnesium (69 mg/kg), Vanadium (438 mg/kg), Calcium (0.22%), Potassium (0.08%), Magnesium (0.11%), Sulfate (0.062%), and Aluminum (0.065%) ^[26][27][28][26,27,28]. Although there is little to no information on the nutritive value of FSF, its richness in trace elements such as Zn, S, Cu, and Fe qualifies it as a possible solution to there being low levels of these minerals, especially in semi-arid regions, resulting in low growth rates and poor quality of livestock. Moreover, since it supplies more than 14 trace elements and other elements that are usually not available in abundance in most field crops [28], it may be used to correct nutritional mineral imbalances in livestock. A review by Ikusika et al. [9] details the physical and chemical properties of FSF as well as its uses in the animal industry and other human activities; readers are, therefore, encouraged to refer to this researchticle. Table 1 further summarizes some studies that have been conducted to research using FSF as a feed additive. Although there was no significant impact of fossil shell flour on poultry, the studies in Table 1 indicate that fossil shell flour influences growth performance parameters, diet digestibility, feeding behavior, feed acceptability/preference, and body condition score, with each improving with increased inclusion levels of FSF up to 6% or 60 g FSF/kg in sheep. In the study by Adeyemo [27], the authors have attributed the efficacy of the broilers to convert nutrients from feed into body tissue to the fact that fossil shell flour inclusion in animal diets daily tends to keep the animals free of parasites (particularly, worms) and toxic chemicals so they can reap maximum benefits from the feed and water they consume. However, it is not clear which compound in FSF is directly related to this phenomenon. The authors also reported an imbalance between calcium and other minerals in the diet, although there was a concomitant increase in the phosphorus content up to 1.5% inclusion of fossil shell powder, after which the phosphorus level dropped. The study by Ikusika ^[29][30][29,30] attributed the improved feeding behavior and/or acceptability of feed by rams to the rich Sodium, Calcium, Potassium, and Magnesium contents in FSF which improves the taste and aroma of the diets. The studies in Table 1 have, therefore, attributed the different effects of FSF on different animal parameters to its mineral content; however, there is no clear indication of the specific contribution of each element and which compound led to a specific result.