Ruminal fermentation and lipid metabolism in lambs fed carob germ as a total replacement for soybean meal

The potential of carob ( Ceratonia siliqua L.) germ as a sustainable, locally available protein-rich and energetic alternative to soybean meal and maize in lamb diets was evaluated. Twenty-seven Valle del Belice × Pinzirita male lambs were assigned to three dietary treatments: control diet (CON), and two experimental diets in which carob germ replaced 33% and 65% of maize and 50% and 100% of soybean meal (C25 and C50, respectively). Diets were offered ad libitum for 56 days. Rumen fermentation parameters and lipid metabolism in meat were assessed. Carob germ inclusion decreased propionate concentration, while butyrate concentration increased. The acetate:propionate ratio increased linearly with carob germ inclusion in the lambs’ diets. No relevant effects were observed on the ruminal and abomasal fatty acid profile, except for slight changes in oleic acid at the highest inclusion level (C50). Likewise, meat lipid showed similar fatty acid profiles between dietary treatments. These results indicate that carob germ can completely replace soybean meal and partially replace maize in lamb diets without impairing ruminal fermentation, biohydrogenation processes or fatty acid deposition in tissues. The use of carob germ could represent a promising strategy to reduce feed-food competition and improving the sustainability of ruminant production systems, particularly in Mediterranean regions where carob is largely produced.