Effects of natural additives as an alternative to ionophores on performance and carcass traits of Nellore cattle in feedlot submitted to transport stress

The present study aimed to evaluate the use of natural additives, based on essential oils and yeast cell wall products, as alternatives for monensin as a growth promoter for beef cattle. A total of 160 Nellore bulls with an average initial body weight of 352 kg were randomly distributed (40 animals/treatment) in four collective pens equipped with 24 automatic feeders (6 devices per pen). The feedlot period lasted 116 days, with a 14-day period of animal adaptation to the facilities. After the adaptation period, a transport stress (8 hours/400 km) was induced in all animals to simulate a commercial feedlot situation. The treatments were: 1) CON - Negative control (no additive); 2) MON - Monensin (27 mg/kg of dry matter (DM)); 3) EO - Essential oil-based additive (Valkalor Plus: 1.3 g/ kg DM); 4) EOYW - Essential oil and yeast cell wall-based additive (Viandi Plus: 1.8 g/ kg DM). The EO additive Valkalor Plus (IDENA®, Sautron, France) consists of a blend of essential oils (eugenol and geranyl acetate), while the EOYW additive Viandi Plus (IDENA®, Sautron, France) contains a combination of essential oils (linalol and geranyl acetate) with yeast cell wall. All statistical analyses were performed in SAS version 9.4 (SAS Institute Inc.), using GLIMMIX procedure and comparing the least square means by Tukey’s test at P < 0.05 and tendency between 0.05 < P < 0.10. A tendency (P = 0.091) and a significant effect (P = 0.032) were observed for final body weight (FBW) and average daily gain (ADG), respectively. Treatment MON presented greater FBW and ADG compared to CON (546 kg; 1.656 kg/d vs. 529 kg; 1.486 kg/d) but did not differ from treatment EO and EOYW. Dietary treatment EOYW presented greater dry matter intake (DMI), compared to MON (7 %; P = 0.006), but did not differ from CON and EO (P > 0.10). On the other hand, dietary treatment MON presented greater gain: feed ratio than all other treatments (P = 0.003). The treatments CON and EO presented greater presence of liver abscesses compared to MON and EOYW (P = 0.030). On average, the presence of liver abscess was 4.62 % for MON and EOYW vs. 23 % for CON and EO. Animals fed EO and EOYW diets, particularly during the initial adaptation period (0–12 days), had greater fluctuations in DMI compared to bulls fed CON and MON diets (P < 0.0001). Bulls treated with MON spent more time eating and had a greater DMI rate (min/kg; P < 0.0001) per kg compared to EOYW bulls during both the adaptation phase and the entire study period. In terms of daily feeding behavior, MON and EO-treated bulls exhibited more visits than EOYW bulls throughout the adaptation, final, and overall study periods (P < 0.0001). The serum haptoglobin concentration was greater for animals fed EO and EOYW compared to other treatments on average and at d 116 after enrollment (P < 0.0001). Altogether, these outcomes indicate that EOYW may be a viable alternative to MON in feedlot diets for finishing animals.