PSLBII-19 Effects of high-forage backgrounding duration on dry matter intake during the early finishing phase

Abstract The adaptation of animals to high-concentrate diets is crucial for optimizing performance in the finishing phase. However, the transition to concentrate-rich diets can lead to metabolic disorders and fluctuations in feed intake. Typically, the same adaptation protocol is used regardless of the previous feeding history of the animal. However, it is possible that the backgrounding period duration may influence initial feed intake and subsequently affect animal performance in the finishing phase. Thus, the objective of this study was to evaluate the effects of implementing different high-forage backgrounding (HFB) durations on daily dry matter intake (DMI) and DMI variance over a 28-d period following the 14-d step-up adaptation to the finishing diets of Nellore bulls. Young Nellore bulls [n = 36; average initial body weight (BW) = 265.25 ± 5 kg; age = 7 ± 1 mo] were used in a completely randomized design and assigned to one of four treatment groups (n = 9/group): 0 (HFB), 28 (HFB28), 56 (HFB56), or 84 (HFB84) d of HFB before starting the 14-d step-up adaptation period to the finishing phase. The HFB diet consisted of 800 g/kg of sorghum silage and 200 g/kg of concentrate, while the finishing diet contained 200 g/kg of corn silage and 800 g/kg of concentrate. The diets were formulated according to BR-CORTE (2016) to achieve ADG of 0.4 kg/d during the HFB phase and 1.2 kg/d during the finishing phase. All animals were fed for ad libitum intake in an electronic feeder (INTERGADO, Intergado Ltd., Contagem, MG, Brazil), and individual daily feed intake was recorded. Additionally, DMI variance was calculated for each bull from daily DMI data over the 28 d of the finishing phase after the 14-d step-up period. Data were analyzed using the MIXED procedure of SAS (SAS Inst. Inc., Cary, NC) assuming the significance level of 0.05. The Tukey test was employed to compare means. Daily DMI was analyzed as repeated measures. The HFB duration had no influence on average DMI of the first 28 d of the finishing phase (P = 0.10; Averages per treatment (kg/d): HFB0 = 7.34, HFB28 = 6.53, HFB56 = 6.71, HFB84 = 6.02). However, a significant interaction was observed between treatments and day on finishing phase (P < 0.001), indicating that the effects of different HFB duration may vary over time during the finishing phase, influencing the daily DMI. Furthermore, the HFB84 presented a higher DMI variance, while the remaining treatments did not differ significantly among themselves (P < 0.001; Averages per treatment: HFB0 = 0.927, HFB28 = 0.616, HFB56 = 0.980, HFB84 = 3.487). In conclusion, the HFB84 increased the variation in daily DMI after adaptation to the finishing diet, indicating that a longer adaptation period may be needed for animals fed high-forage backgrounding diets for longer durations.