Effect of weaning strategy and backgrounding management on growth performance, carcass characteristics, and mRNA expression in the longissimus muscle of beef steers

Abstract

We evaluate the effect of the weaning strategy (WS; early, 130 ± 21 d vs normal, 187 ± 20 d) and backgrounding management (BGM) on growth, carcass characteristics, and relative mRNA expression in the longissimus muscle (LM) of beef steers. One hundred and twenty Angus × SimAngus-crossbred steers (body weight (BW) = 130 ± 11.2 kg) were used in a randomized complete block design. Steers, blocked by age and BW, were randomly assigned to 1 treatment (2×2 factorial). Treatments consisted of early weaned (EW) or normal weaned (NW) steers subsequently backgrounded (BG) on either a forage-based (FB) or concentrates-based (CB) diet. The EW steers (d 0) were ad libitum-fed a grain-based diet for 49 d until nursing calves were NW. Steers were ad libitum-fed either a FB diet for 214 d or a CB diet for 95 d afterward. Steers were finished on a high grain diet until harvested at an estimated constant 12 th rib fat thickness (1.5 cm). Expression of mRNA in the LM was measured over time. Data were analyzed using PROC MIXED in SAS. The EW steers were heavier (P ˂ 0.01) at the beginning of the backgrounding and finishing period. When the finishing phase began, steers FB were heavier (P ˂ 0.01) than CB steers. There was a tendency for a WS × BGM interaction (P = 0.08) for final BW, where NW-FB steers were heavier than the steers on the other 3 treatments, which do not differ between them. In the finishing phase, steers BG on a FB diet had greater dry matter intake and ADG, but lower gain to feed ratio (P ˂ 0.01). There was a WS × BGM interaction (P = 0.03) for days on feed (DOF) in the finishing diet, where backgrounding steers in a FB diet decreased DOF required to reach the harvesting target among EW steers, but not within NW steers. No interactions or treatment effects (P ≥ 0.17) were detected for marbling score (MS). For ZFP423, EW steers showed a greater mRNA expression on d 112 and a lower expression on d 255 than NW steers (P ˂ 0.01). In d 57, steers BG on a CB diet presented a greater DLK1 mRNA expression than steers BG on a FB diet, whereas in d 255, this was inverted (P ˂ 0.01). For C/EBPD mRNA expression, a tendency for a WS × BGM interaction was observed (P = 0.06), where a greater expression of C/EBPD was observed in steers BG on a FB diet among EW steers, but not within NW steers. In this study, early grain feeding followed by different backgrounding management does not support MS improvements of beef carcasses.

Effect of Post-Weaning Concentrate Feeding Prior to Forage Finishing on Intramuscular Fat Deposition

“…Early-weaned steers had a greater expression of ZFP423 during the backgrounding phase (d112), whereas normal-weaned steers had a greater expression of ZFP423 during the finishing phase (d 255). It was also observed that DLK1 expression was greater for steers that were backgrounded on concentrate-based diets than forages early in the backgrounding phase but not in the finishing phase [21]. The expression of transcription factors (PPARg and SREBP1c) was not altered, but their activators (PGC1a and SCAP) were down-regulated with concentrate feeding (PW120) compared to PW0.…”

“…A change in ZFP423 but not Pref1 provides mixed results regarding if changes in adipocyte hyperplasia are involved in IMF deposition with concentrate feeding post-weaning. Others [21] have reported that feeding concentratebased diets during the post-weaning phase altered ZFP423 expression, but these changes were dependent on the time of weaning. Early-weaned steers had a greater expression of ZFP423 during the backgrounding phase (d112), whereas normal-weaned steers had a greater expression of ZFP423 during the finishing phase (d 255).…”

“…The results of this study demonstrate that steers can be fed high-concentrate diets for 120 d post-weaning to enhance the marbling deposition and produce a high percentage of Choice carcasses after finishing on forages. Pittaluga et al [21] examined early versus normal weaning on forage-or concentrate-based diets in steers and reported that the marbling score at harvest was not altered by the timing of weaning nor the backgrounding management.…”