Effect of Combining the Ionophore Monensin with Natural Antimicrobials Supplemented in the Last Phase of Finishing of Lambs: Growth Performance, Dietary Energetics, and Carcass Characteristics

With the aimof evaluating the effect of combining an antibiotic ionophore with plant extracts and probiotics on the productive efficiency (performance and carcass) during the last phase of lamb fattening, 24 Pelibuey Chi Katahdinmale lambs (38.47 +/- 3.92 kg, initialweight) were fedwith a high-energy diet during for 56 days, and assigned, under a complete randomized block design experiment to one of the following supplement treatments: (1) 28mg ofmonensin/kg diet DMsupplemented alone (MON), (2) combination ofMON plus 2 g/kg diet of a product contained Bacillus subtilis 2.2 +/- 10(8) CFU kg diet DM(MON + BS), (3) combination ofMON+ BS plus 300mg essential oils/kg diet DM(MON+ BS + EO), and (4) BS alone. At the end of the feeding trial (56-d), lambs were slaughtered and carcass variables weremeasured. Compared to the rest of the treatments, combiningMONwith BS improved dietaryNE by 3.4% and the efficiency of utilization of dietary energy consumed. Inclusion of EO in theMON + BS combination resulted in a similar average dailyweight gain (ADG) and feed efficiency (GF) when comparedwithMON+ BS, but showed a lower dietary net energy (NE), hot carcass weight, and dressing percentage. Lambs receiving BS alone showed greater average ADG and dry matter intake (DMI) than lambs receiving MON + BS + EO, but similar feed GF and dietaryNE. Therewere no treatment effects on tissue composition, whole cut, or visceral organ mass. It was concluded that combining probiotics with the ionophore monensin can improve the efficiency of dietary energy utilization in the last phase of finishing. Probiotics supplemented alone result in greater ADGwithout a difference in dietary energy efficiencywhen comparedwithMONalone. Inclusion of EO in theMON+ BS combination did not showadvantages; on the contrary, it reduced carcassweight and dressing percentage. It is necessary to further research the potential complementary effects of combining diverse sources of natural additiveswith synthetic antibiotics.