362 Late-Breaking: Use of wheat straw and oilseed fines in diets for gestating beef cows.

Incorporating byproducts and crop residues such as oilseed fines and wheat straw into beef rations could improve sustainability, mitigate feed shortages during droughts, and reduce costs. The objective of this study was to evaluate the effect of feeding a wheat-straw based diet with high- or low-fat oilseed fines [added to achieve 6% fat on diet dry atter (DM) basis] on dry matter intake (DMI), average daily gain (ADG), body condition score (BCS), rib fat, and rump fat of beef cows during the 2nd and 3rd trimesters of gestation. Seventy-two pregnant crossbred beef cows were selected and stratified by BW, BCS, age, parity, and days pregnant and randomly allocated to 12 pens (6 cows/pen). Each pen was randomly assigned to a diet treatment (4 replicates/ treatment). The experiment was set up as a completely randomized design and lasted 126 d. The diet treatments were: 1) a control diet with barley silage and hay; 2) a diet of wheat straw with low-fat (8.24%) oilseed fines; and 3) a diet of wheat straw with high-fat (19.27%) oilseed fines. All diets were formulated to be isoenergetic (~60% TDN) and the diets with fines both contained 6% ether extract. Statistical analysis was conducted using the MIXED procedure of SAS (SAS Institute Inc.) with dietary treatment included as a fixed effect. Repeated measures were used for BCS, and rib and rump fat measurements. Differences among treatment means were separated using Tukey’s test and were declared significant when P≤0.05. There were no differences among treatments for initial BW (665 kg; P = 0.83), final BW (805 kg; P= 0.48), or ADG (1.10 kg/d; P= 0.41). Cows fed high-fat oilseed fines had lower (P <0.01) DMI as a % of BW than cows fed the control and low-fat oilseed fines treatments. However, DMI expressed in kg/d was lower for cows fed either the high-fat or low-fat oilseed fines treatments (P<0.01) when compared to the control diet. There were no differences among treatments for BCS, rib fat, and rump fat; however, these increased (P<0.01) for all cows from d 1 to 63 to 126. In conclusion, wheat straw diets that include high- or low-fat oilseed fines promoted similar BW change as cows fed a barley silage and grass-hay control diet but consumed less feed likely due to the greater concentrations of dietary fat.