# Carcass Yield and Meat Quality of Broiler Chicks Supplemented with Yeasts Bioproducts
## 1 Introduction  
The future use of synthetic additives (vitamins, proteins, and pigments) in broiler chicks' feeds poses a number of problems [1] including competitive availability, increased productive induced costs, and health risks associated with sole ingredients commonly used in human and animal feeds and food. Moreover, the projection concerning the increased demand for broiler meat and meat products is directly affected by the consumer's choice. Recently, consumers' preferences are directed towards safe and high-quality broiler meat and meat products, often associated with slow-growing broiler breeds [2], reared in organic systems [3], obtained using an economic circular approach by introducing organic valuable waste and by-products [4].  
After twelve-fifteen successive fermentation batches, the brewing biological catalyst _Saccharomyces cerevisiae_ loses its vitality and viability and might be biologically compromised, being no longer appropriate for beer production. Brewers' spent yeast (SC) was previously described as a nutritive complex ingredient, an excellent source of protein (more than 40%) [5], presenting a high content of essential limitative amino acids, with high levels of biotin, folic acid, microelements, and intracellular flavoring compounds [6, 7]. It is known that _Saccharomyces cerevisiae_ (SC) consumption as a protein source for animal and human nutrition is restricted, due to the high level of nucleic acids (up to 15%), mainly causingseric and tissue uric acid accumulation [8]. Despite these facts, SC was mainly subjected to debittering, efficiently valuing all biologic active compounds [9], that can conventionally be achieved by physical, chemical, and biological processes [10], while avoiding toxicity [11].  
Poultry cannot synthesize carotenoids; synthetic pigment feed additives are often employed in order to adjust the retinoic acid ratio via carotenoid dietary supplementation. Most commonly used food and feed colorant additives in poultry nutrition are xanthophylls (canthaxanthin, astaxanthin, and zeaxanthin) that originate from almost 90% mainly synthetic resources. Nowadays, poultry meat consumers' preference is directing the meat producing sector towards organic and less intensive poultry rearing techniques, including the use of natural and organic feed coloring additives. Recent scientific evidence points out the advantages of employing microbial pigment sources, lowering the costs covering the geo-climate variability and time spent on the vegetal pigment producing industry, obtaining a short-time valuable pigment product, mostly based on waste fermentation, and low-cost materials [12; 13; 14]. Yeast such as _Rhodotorula muclaginousa_ (RM) represents a perfect choice as a natural resource of secondary metabolites: carotenoids, lipids, and extracellular enzymes [13; 15; 16].  
Previous studies indicate an active/inactive SC dietary supplementation improves broiler growth performance [11; 17; 18], immunity response [13], carcass yield [17], and meat quality [19; 20]. Scientific evidence for using RM on broiler chick feed is very limited [21], but recent studies suggest that it could have growth promoting, health promoting, and production quality effects on laying hens [22], fish [23], and swine [24].  
The study was performed to probate the hypothesis that yeasts lyophilized lysates dietary supplements might impair the carcass yield and the meat quality attributes. Therefore, the main goals were to evaluate the singular and the interaction effects of the dietary yeasts lyophilized lysates supplements on the broiler carcass yield and breast and thigh meat quality attributes (pH, color, proximate chemical composition, texture profile analysis, and sensorial evaluation).