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

Abstract Text: 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 12^th rib fat thickness were evaluated in crossbred cattle (n=628) fed for two 70d periods. During the growing period (first 70d), 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 12^th 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 intake period, DMI for grain-fed steers were evaluated for 7, 14, 21, 28, 35, 42, 49, 56, or 63d. All intake evaluation periods were correlated (r≥0.72; P<0.01) to total DMI during the growing phase and overall DMI. Intake of forage and forage RFI during the growing phase were correlated (r=0.58; P<0.01, and r=0.42; P<0.01, respectively) to intake of grain and grain RFI during the finishing period in heifers. Forage ADG was negatively correlated (r=-0.30; P<0.01) grain ADG. In conclusion, intake and efficiency were repeatable from growing to finishing periods. Although gain was not repeatable for growing and finishing periods, each test period was correlated to gain over the entire feedlot phase. Correlations between shorter duration intake evaluation periods and overall DMI suggest that the intake evaluation period can be shortened to 35d. Intake and feed efficiency on forage and grain were moderately correlated.

Keywords: beef cattle, feed efficiency, intake