Effects of backgrounding rate of gain on carcass characteristics

Abstract Text:

Different rates of gain during the backgrounding phase have been shown to impact subsequent live cattle performance, but less is known about the impact of backgrounding ADG on carcass characteristics.  The objective of this study was to evaluate rate of gain during the backgrounding phase on HCW and marbling in steers harvested at a common fatness.  Steers were randomly allotted to 1 of 3 backgrounding growth rates (BGR) of: 1) 1.36 kg ADG, 63 d; 2) 1.14 kg ADG, 79 d; and 3) 0.91 kg ADG, 93 d from 316 kg to 398 kg BW.  Steers on treatment 2 and 3 were limit fed the basal corn silage diet to achieve the targeted ADG while maintaining similar profiles of fermentable carbohydrates.  At the end of backgrounding steers were switched to a common finishing diet.  Steers were harvested, as a treatment, at a common 12^th rib fat thickness.  Pen basis data were analyzed as a completely randomized design using PROC GLM (SAS) with 10 pens/BGR and 8 steers/pen.  Cold stress corrected backgrounding ADG were 1.38 kg, 1.15 kg, and 1.00 kg (P<0.001) among BGR 1 to 3, respectively and G:F decreased (0.153, 0.138, 0.135; P<0.001) as BGR decreased due to treatment.  Total days required to reach common fatness and 12^th rib fat were 187 d (1.39 cm), 201 d (1.39 cm), and 212 d (1.36 cm) for BGR 1 to 3, respectively. During the finishing phase ADG (1.63 kg, 1.77 kg, and 1.86 kg) increased linearly (P<0.05) and the DMI (10.26 kg, 10.49 kg, and 11.10 kg) response was quadratic (P<0.05) as BGR decreased.  The finishing G:F response was quadratic (0.159, 0.169, 0.167; P<0.001) as BGR decreased.  Hot carcass weight (373 kg, 385 kg, 389 kg) increased linearly (P<0.05) as BGR decreased.  Marbling score response to BGR was quadratic (Sm70, Sm85, Sm54; P<0.05) for BGR 1 to 3, respectively.  Other carcass characteristics were similar (P>0.05) among treatments.  The linear response in HCW and quadratic response of marbling suggest that for a given frame size of a calf there is an ideal backgrounding rate to optimize carcass quality and value.  An excessive BGR caused the accumulation of total body fatness to exceed intramuscular fat accretion.  Consequently steers finished prematurely with no advantage in marbling.  Conversely, if the BGR was too low, marbling was lower even though steers were fed to a common fat end point at a heavier BW.

Keywords: cattle, backgrounding, marbling