An in vitro evaluation of fat-extracted Pongamia seedcake in barley-based feedlot diets

Eslam Ahmed^1,2Mingbo Ni¹Alex V Chaves³Sarah Jade Meale^1*

• ¹The University of Queensland, Brisbane, Australia
• ²South Valley University, Qena, Egypt
• ³The University of Sydney, Sydney, Australia

There is growing interest in finding alternative sustainable feed ingredients in ruminant diets. This study evaluated four processed pongamia seedcake meals (PSC), three processed using a proprietary extraction method, compared to one processed using traditional hexane extraction, in two separate in vitro experiments. Experiment 1 assessed PSC as a partial replacement for conventional protein meals (canola and cottonseed) with a total inclusion level of 0, 4 or 8% DM. Experiment 2 assessed PSC as a partial replacement for an energy source (barley grain) with a final inclusion level of 0, 12, 15 or 30% DM. There was no interaction of level x processing type (type) in either experiment (P≥0.10). Experiment 1 demonstrated that neither the type nor level of PSC had an effect on methane production (ml/g digested DM). Replacement of canola or cottonseed meal with PSC reduced (P < 0.01) IVDMD by an average of 7% across all PSC types and inclusion levels, compared to the control. However, the concentration of total volatile fatty acids (VFA) was not affected by either PSC type or level. Experiment 2 showed that inclusion of PSC in a barley-based diet increased (P < 0.01) methane production (mL/g digested DM) by up to 20.8%, compared to the control. Compared to the control, IVDMD was not affected by PSC inclusion up to 15% DM (P > 0.05). However, processing type of PCS had varying effects, where PSC4 (hexane extracted) had 5.5% greater IVDMD (P = 0.02) compared to PSC1, and 3.8% compared to PSC2, but was similar to PSC3, all of which were processed using novel extraction methods. These findings suggest that novel processed PSC has potential as a feed ingredient, but its application requires careful consideration. While it can replace conventional meals without reducing total VFA production, this may come at the cost of reduced diet digestibility. Furthermore, when used to replace barley grain, PSC inclusion may increase methane production. The suitability of PSC depends on the extraction method, its inclusion level, and the dietary component it replaces.