Effect of harvest method on corn residue quality and RUP supplementation on residue quality and performance of growing calves

Abstract Text: Technology advancements in harvesting techniques of corn residue may improve forage quality by reducing the proportion of the stem in the bale.  Even with higher quality residues, metabolizable protein supplementation may be needed to achieve the desired performance of growing calves on a corn residue-based diet.  The objectives of this study were to determine 1) the effect of harvest method on forage quality and steer performance in growing diets and 2) the effect of supplemental RUP on steer performance in residue-based growing diets. The experiment was designed as a 2 x 2 + 1 factorial arrangement of treatments using 60 crossbred steers (initial BW = 283; SD = 32 kg; n = 12).  Factors were 3 corn residue harvest methods (low stem, high stem, and conventional) and supplemental RUP included as a 50:50 blend of Empyreal^® 75 and SoyPass^® at two levels (0, 3.3 % diet DM).  Steers fed the low stem residue diet had the greatest ADG (0.78, 0.69, 0.63 ± 0.07 for low stem, high stem, and conventional, respectively; P < 0.05), and consequently a greater ending BW (345, 338, 334 ± 6 kg for low stem, high stem, and conventional, respectively; P < 0.05) compared to the conventionally harvested corn residue.  The low stem residue bales have a greater proportion of husk and leaf which are more digestible than stems and cobs. Results from in vitro organic matter digestibility show low stem residue had greatest digestible organic matter amount (60.3, 53.5, 54.8% for low stem, high stem, and conventional, respectively; P < 0.05) compared to the other two residue methods.  The high stem residue diet showed no improvements over the conventional corn residue diet, which is likely due to the high stem bales containing a similar proportion of stem as the conventional bales.  In situ results showed no difference in RUP content (40%) and RUP digestibility (60%) amongst the three residues.  The addition of RUP resulted in an improvement in ADG (0.66, 0.58 ± 0.06 for supplemental RUP and no RUP, respectively; P = 0.08), and G:F (0.25, 0.21 ± 0.03 for supplemental RUP and no RUP, respectively; P = 0.02) compared to the same diets without the additional RUP.  Changing the harvest method of the residue improves forage quality over conventionally harvested residue.  Supplemental RUP can increase gain and improve feeding efficiency in growing steers consuming corn residue-based diets. 

Keywords: Growing, Residue, Rumen Undegradable Protein