PSIII-6 - Evaluating lupin grain as an alternative protein source in diets for winter-lot-fed beef calves

Abstract: This study aimed to evaluate the effects of graded levels of lupin grain (LG, Lupinus angutifolius) replacing sorghum dried distillers’ grains with soluble (DDGS) on the growth performance and feed-to-gain ratio of winter-lot-fed beef cattle. Conducted over 84 days in 12 open-air pens, the study involved 48 spring-born castrated Hereford calves (8-9 months old, 212 kg), blocked by prior management (early weaning in pens; on pasture; conventional weaning). Calves were randomly assigned to four pens within block and to one of four diets with LG inclusion levels of 0%, 10%, 20%, or 30% replacing DDGS (dry matter basis). The 0% LG diet included sorghum silage (24%), sorghum grain (30%), DDGS (30%), and a mineral and vitamin premix (16%), providing 16% CP across treatments. Calves were gradually introduced to the diets and fed ad libitum throughout the study. Body weight (BW) was recorded biweekly, while dry matter intake (DMI) was measured daily. Average daily gain (ADG) and mean feed-to-gain ratio (FGR) were calculated for the experimental period. At the beginning and end of the study, hip height, ribeye area (REA), and backfat thickness (BF) were measured, with REA and BF assessed using ultrasonography. Data were analyzed using a randomized block design with treatment and block as fixed effects and the pen as the experimental unit (three pens per treatment, four calves per pen). Linear and quadratic effects of LG levels were tested. Initially, no significant differences were found between treatments (P ≥ 0.10) for growth and tissue deposition variables: BW (211.8 kg), hip height (104.4 cm), REA (37.0 cm²), and BF (2.10 mm). Replacing DDGS with LG significantly affected animal growth, with quadratic responses (P ≤ 0.01) for ADG (y = -0,0007x2 + 0,0253x + 1,318), final BW (y = -0,063x2 + 2,184x + 325,29) and BF (y = -0,0063x2 + 0,2265x + 4,915). Maximum ADG (1.55 kg/d), BW (344.2 kg), and BF (6.95 mm) were achieved with LG inclusion levels of 17% to 18%. No significant effects were observed on final hip height (121.4 ± 0.99 cm; P ≥ 0.05) and REA (55.1 ± 1.3 cm²; P ≥ 0.05). DMI decreased linearly with increasing LG inclusion (P ≤ 0.01), with the highest DMI at 0% LG (8.6 ± 0.22 kg/d), resulting in a 36% reduction in DMI at total DDGS replacement. FGR also decreased linearly (P ≤ 0.01), with the diet without LG showing a FGR of 6.5 ± 0.31, decreasing by 95 g for each 1% increase in LG inclusion. These results indicate that lupin grain is a viable alternative to DDGS as a source of energy and protein in feedlot calf diets, improving animal performance and feed conversion efficiency at inclusion levels up to 18%.