PSIII-5 - Effects of whole or cracked lupin grain (Lupinus angustifolius) supplementation on growing cattle grazing summer annual grasses

Abstract: This study aimed to assess the impact of supplementing whole or cracked lupin grain (Lupinus angustifolius) on the summer growth performance, forage utilization, and supplement conversion ratio of beef cattle grazing forage sorghum (Sorghum cv 135 BMR). The experiment was conducted from December 30, 2021, to March 7, 2022. Fifty-four Hereford steers (270 ± 52 kg) blocked into three groups by initial shrunk body weight (BW) were randomly assigned within block to three grazing paddocks, each receiving one of three treatments: a control grazing without supplementation (CON), or daily supplementation with 1 kg per 100 kg BW (DM basis) of lupin grain (27.3% CP), offered either whole (WL) or cracked (CL). Pasture was rotationally grazed in seven-day strips with a forage allowance of 8 kg per 100 kg BW, adjusted weekly. To minimize heat stress, cattle were moved to a shaded area from 10 AM to 5 PM, divided into nine pens (one per replication) with ad libitum water. The supplement was provided in the pen upon arrival. Cattle were weighed every two weeks, and daily supplement intake was estimated as the difference between offered feed and refusals. Average daily gain (ADG), forage utilization, and supplement conversion ratio (SCR) were evaluated over the grazing period. SCR was calculated as the ratio of supplement consumption to ADG response from supplementation. Data were analyzed using a randomized block design, with treatment and block as fixed effects, and the grazing paddock serving as the experimental unit (3 paddocks per treatment, 6 steers per paddock). Treatment means were compared using orthogonal contrasts: CON vs. (WL + CL) and WL vs. CL. Pre-grazing biomass and height for sorghum (10.981 ± 569 kg DM/ha; 96 ± 1.6 cm) and chemical composition (7.3% CP) did not differ between treatments (P ≥ 0.05). Supplementation and grain processing had no effect on forage utilization (53.3% ± 3.2; P ≥ 0.05). Compared to the control, lupin grain supplementation improved average daily gain (ADG) (0.952 kg/d vs. 0.229 kg/d ± 0.15; P ≤ 0.01) and final body weight (335.0 kg vs. 263.3 kg ± 7.8; P ≤ 0.01), resulting in a SCR of 4.4 ± 0.24. No differences were found in daily supplement intake due to processing (0.98 kg/100 kg BW ± 0.003 for both WL and CL; P ≥ 0.05). Cracking lupin grain did not affect ADG (WL: 0.905 kg/d vs. CL: 0.999 kg/d ± 0.18; P ≥ 0.05) or SCR (WL: 4.62 vs. CL: 4.11; P ≥ 0.05). This study demonstrates the viability of using whole lupin grain as a supplement to enhance the growth rates of steers grazing forage sorghum.