The effect of different dietary ionophores and inclusion levels in the finishing diets of lambs

[摘要] English: The aim of this study was to evaluate the effects of different ionophore types and inclusion levels in feedlot finisher diets on production performance and carcass characteristics of S.A. Mutton Merino lambs. To address the aim of the study, it was divided in two phases namely: firstly, to evaluate the effect of different ionophores on animal production and carcass characteristics and secondly, to evaluate the effects of different dietary ionophore inclusion levels on the same experimental parameters. During the first study (63 days) 60 lambs (29.7 ± 2.5 kg) were randomly allocated to four treatment groups (n=15/treatment) and further subdivided into five replicates (n=3/replicate). Monensin, lasalocid and salinomycin was included into a commercial high protein concentrate (379 g CP/kg DM) at 16.5, 33.0 or 17.5 mg active ingredient/kg feed, respectively. The fourth treatment, namely the control diet was without any ionophore inclusion. Treatment diets (164 g CP/kg DM; 179 g NDF/kg DM) consisted of this protein concentrate (200 g/kg; containing an ionophore or not), maize meal (650 g/kg) and lucerne hay (150 g/kg) representing the four dietary treatments: control (C: no ionophore inclusion), monensin (M), lasalocid (L) and salinomycin (S). During the second study (42 days) 84 (30.7 ± 2.7 kg) lambs were randomly allocated to seven dietary treatment groups (n=12/treatment) and further subdivided into four replicates (n=3/replicate). Treatment diets of the second study consisted of the same basal diet used during the first study, differing only in respect of ionophore type and inclusion level; representing the control (no ionophore included), monensin low (ML: 11 mg active ingredient/kg feed), monensin medium (MM: 16.5 mg active ingredient/kg feed), monensin high (MH: 22 mg active ingredient/kg feed), salinomycin low (SL: 15 mg active ingredient/kg feed), salinomycin medium (SM: 17.5 mg active ingredient/kg feed) and salinomycin high (SH: 20 mg active ingredient/kg feed) treatments. Generally, neither ionophore type nor inclusion level had an effect (P>0.05) on any of the production performance parameters, as well as carcass characteristics determined in both studies. However, in the first study, salinomycin resulted in the highest (P<0.0001) NDF intake (1000 g/lamb/day), whereas monensin included at 22 mg/kg resulted in the lowest (P<0.01) CP (377 g/animal/day) and ash (83 g/animal/day; P<0.01) intake during the second study. In general, the efficiency of monensin, lasalocid and salinomycin, even at different levels, in sheep finisher diets, seem to be similar and does not affect rumen fermentation in such a way to improve feedlot performance and carcass characteristics of lambs when compared with the control treatments.

[发布机构] University of the Free State