Effects of restricted vs. step up dietary adaptation for 6 or 9 days on feedlot performance, feeding behaviour, ruminal and blood variables of Nellore cattle

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Worldwide, the demand for beef has been increasing, as well as the beef production in the last three decades (Bruinsma, 2003). Moreover, the beef exports around the globe increased 25% from 2006 to 2014 (ANUALPEC, 2015). In response to the increasing world beef demand, cattle producers have increasingly adopted the feedlot system over the last 20 years to increase efficiency and beef production (ANUALPEC, 2015). In addition, concentrate has been replacing roughage, as reported on two surveys with Brazilian beef cattle nutritionists, where the proportion of concentrate ingredients in finishing diets increased from 71.2% (Millen, Pacheco, Arrigoni, Galyean, & Vasconcelos, 2009) to 79.0% (Oliveira & Millen, 2014).
Increasing the concentration of grains in cattle diets promotes changes in feeding behaviour (Missio et al., 2010), which often leads to reduced performance when animals are adapted for less than 14 days (Brown, Ponce, & Pulikani, 2006). Based on this fact, an adaptation period of 21 days, regardless of protocol, has been recommended in the USA (Vasconcelos and Galyean, 2007). However, in the USA, the finishing diets fed to feedlot cattle contain more energy than diets fed at Brazilian feedlots (1.50 vs. 1.22 net energy/kg of dry matter [DM] respectively), as well as cattle stay for longer periods at the US feedlots until reach the desirable slaughter weight (Oliveira & Millen, 2014). Also, protocols currently used for cattle adaptation to high grain diets were developed using Bos taurus taurus. However, most of the Brazilian beef herd is composed of Bos taurus indicus (Nellore). Based on the facts just described, previous studies have been conducted to determine if shorter periods of adaptation would negatively impact the performance and the rumen epithelium of Nellore cattle. Parra et al. (2011) conducted a trial containing 120 22‐month‐old Nellore bulls, in a 2 × 2 factorial arrangement of treatments (step up and restriction protocols for 21 and 14 days), and reported heavier hot carcass weight (HCW) and increased dressing percentage for Nellore cattle adapted for 14 days when compared to those adapted for 21 days, regardless of the protocol adopted. Consequently, Barducci et al. (2012) used the same design just described replacing 21 days for 9 days of adaptation and did not observe any differences between cattle adapted for either 14 days or 9 days in terms of feedlot performance and carcass traits. However, in a companion study, Carrara et al. (2012) reported smaller ruminal absorptive surface area (ASA) for cattle adapted for 9 days at the end of adaptation period when compared to cattle adapted for 14 days. Therefore, as cattle performance was not negatively affected when adaptation period lasted 9 days, the present study aimed to determine effects of restricted intake of the final finishing diet as a means of dietary adaptation compared with diets increasing in concentrate (step up) over periods of 6 and 9 days on overall feedlot performance, carcass characteristics, feeding behaviour, blood gas profile, lipopolysaccharide‐binding protein and rumen morphometrics of Nellore cattle fed high‐concentrate diets.
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