Is the inclusion of carob (Ceratonia siliqua L.) pulp in the concentrate of weaned light lambs worth it?

This study aimed at evaluating the effects of dietary carob (Ceratonia siliqua L.) pulp, a by-product of the fruit processing industry, on light lamb performances, time budget behaviour, coefficients of total tract apparent digestibility (CTTAD) and blood metabolites. A total of 144 crossbred lambs with 41 ± 5.5 days of age were monitored in two consecutive batches. They were housed in groups of 6 lambs (3 females and 3 males) balanced according to weaning body-weight and assigned to one of three isoenergetic and isoproteic concentrate-based diets: C0 (without carob pulp), C15 (150 g/kg of carob pulp) and C30 (300 g/kg of carob pulp). At 50, 65 and 80 days of age, feed, faeces and blood samples were collected, and behaviour was recorded. The type of concentrate did not have effect on lamb growth and concentrate intake (P > 0.05). However, the concentrate feed conversion ratio (FCR) was higher for C15 and C30 compared to C0 (P < 0.05). The time budget behaviours were not affected by diets (P > 0.05). The time spent lying resting and standing static increased throughout the fattening period (P < 0.05), but self-grooming, feeding, exploration, movement and positive social interactions decreased with age (P < 0.05). Regarding the CTTAD of dry matter (DM), organic matter (OM) and crude protein (CP), it was noted that C30 had the lowest digestibility of these nutrients with respect to C0 and C15 (P < 0.05). Furthermore, the total condensed tannins (CT) content in faeces was higher in C30 compared to C0 and C15 (P < 0.05). The age of lambs affected the CTTAD of DM, OM, CP and phosphorus, which were lower at 50 days than in the rest of control days (P < 0.05). Blood metabolites were not affected by experimental diets (P > 0.05). However, urea concentrations increased significantly from 50 to 65 days of age, while glucose decreased concomitantly (P < 0.05). In conclusion, dietary carob pulp inclusion up to 300 g/kg does not negatively affect animal daily gains, daily activity budgets and metabolic nutritional status, but reduces diet digestibility and increases the concentrate FCR. Although a carob pulp inclusion of up to 150 g/kg in the energy-rich concentrate-based diet for weaned light lambs increases the concentrate FCR while keeping the daily gain, this dietary strategy would be a good trade-off between animal performances and circular economy principles.

This research was funded by the Ministry of Science, Innovation of Spain and the European Regional Development Funds, grant number INIA RTA2017-00008-C02. Jonathan Pelegrin-Valls is in receipt of an early-stage research staff grant by the Generalitat de Catalunya-European Social Funds. We greatly appreciate the technical assistance of Joan Carles Melo and Bonàrea staff during on-farm animal handling and measurements.