379 Effects of diet type and feeding phase on intake and feed efficiency of beef cattle

Abstract

Objectives were to evaluate test period length and repeatability of intake and efficiency measures during the growing and finishing phases, and determine the relationship between intake and efficiency evaluated in cattle fed different diet types. Over a 2-yr period, DMI, ADG, and 12th rib fat thickness were evaluated in crossbred cattle (n = 628) fed for two 70 d periods. During the growing period (first 70 d), a forage-based diet (equal parts corn silage and alfalfa haylage) was fed to heifers and a grain-based diet (50% corn, 15% DGS) was fed to steers. All cattle were fed the grain-based diet for the finishing period (last 70d). Individual DMI was recorded using the GrowSafe (Airdrie, AB, CAN) system. Residual feed intake (RFI) was calculated for each period and was assumed to represent a multiple regression equation, regressing DMI on mid-test metabolic BW, ADG and 12th rib fat thickness. Overall wean to slaughter ADG was calculated for steers by regressing all weights from the start of the growing phase to final BW, calculated as HCW divided by standard dressing percentage (63%). Dry matter intake and RFI were correlated (r = 0.56; P < 0.01, and r = 0.63; P < 0.01, respectively) for growing and finishing periods of steers fed grain. Although, steer ADG was not repeatable (r = 0.11; P = 0.06) across test periods. Growing and finishing ADG were both correlated (r = 0.58; P < 0.01, and r = 0.69; P < 0.01, respectively) to overall ADG. To test the potential of shortening the…