## 1 Introduction  
In the global scenario, Brazil has the largest herd, the principal exporter, and one of the largest consumers of beef in the world [1,2]. However, has been the low productivity and inferior quality. The low productivity of beef in Brazil has been associated with several factors [1], ranging from predominance genetics (zebu and their crosses) to productive factors related to management [2]. Among them, various studies highlight the following of low carcass weight and conformation, low quality forage (predominantly tropical and subtropical grasses), high temperatures for much of the year, deficiency of minerals and energy in the dry season, presence of reproductive and non-reproductive diseases in the herd, late slaughter age, and, above all, lack of business management [3, 4, 5, 6]. During the rearing phase, from born to weaning (7 months), calves remain on low-quality pastures with their respective mothers [4]. These calves are then raised from weaning to puberty (24 months) in extensive systems [4]. The final part of this cycle can be fattening on pastures (90%) and a small part in more intensive systems [1]. Previous studies showed that Zebu (Nellore) and it crosses with Europeans (_Bos taurus_) that average daily gain (ADG) of bulls finished on pasture is low (average of 0.40-0.50 kg/day) [7,8] when compared to bulls finished in feedlots (1.50 to 2.0 kg/day) [9,10]. This is due to the energy and protein density of the diets fed to cattle raised on pasture and finished in feedlots or cattle that have been finished in feedlots since weaning [7,8,11,12]. Feed efficiency is better for animals finished in feedlots when compared to animals finished on pasture. Diets fed to animals finished in feedlots are adjusted to achieve the maximum potential allowed by the genetic potential of the animals [7,8,11,12]. Several studies show that cattle finished in feedlot show a feed conversion from 6.0 to 8.0 kg of dry matter consumed for a gain of 1.0 kg of body weight [9,10,13]. On the other hand, the feed efficiency of cattle finished on pasture with or without supplementation is between 12 to 20 kg of dry matter for 1.0 kg of body weight gain per day [14]. Cattle finished in feedlots have higher slaughter weight and, consequently, higher carcass weight [8,9,13,15]. Cattle finished in feedlot with low or high grains are slaughtered in less time (days) than cattle finished on pasture [7,8]. [PERSON] et al. [8] observed a higher slaughter age for crossbred Red Angus steers finished on pasture than those fed high-grain diets. Angus steers finished in feedlots with a high-grain diet had better carcass dressing than steers finished on pasture [7]. Similarly, [PERSON] et al. [16] observed higher carcass dressing when comparing Angus steers finished with silage and concentrate (62.3%) and steers finished on pasture (54.3%). In addition, higher carcass dressing was observed for Nellore animals when finished in feedlot (58.9%) than on pasture (56.4%). The better carcass dressing in diets with less forage can be explained by the smaller size of the gastrointestinal tract due to the lack of fiber in the diet [17], when comparing conventional feedlot with high-grain diets, found no differences in carcass dressing. In general, it is accepted that the cost of producing pasture-raised cattle is cheaper [4,5,18]. In this context, there would be no need for changes in the breeding, rearing and finishing system of beef bulls. Another important factor is the quality of the meat produced [19,20,21,22]. In addition to meat quality, new issues are being debated, such as animal welfare, environmental protection, among others [23,24,25,26]. Therefore, experts seek new bulls' production systems based on more efficient systems such as genetic material (new breeds and crossbreeds), pasture improvement, use of additives and ionophores, systematic changes in active ingredients in medications, feedlot more professional management [1,27,28].