Effects of initiating dietary narasin, at different production stages, on growth performance and carcass characteristics of growing-finishing pigs

Abstract

Objective

Our objective was to determine the effects of initiating narasin, at different production stages, on growing-finishing pig performance.

Materials and Methods

In Exp. 1, 360 barrows (BW = 23.0 ± 0.13 kg) were used in a completely randomized design (45 pens; 15 replications) with 90-d treatments: (1) an unmedicated diet (CON), (2) 15 mg/kg narasin (NAR-90d), or (3) 11 mg/kg virginiamycin (VIR-90d). In Exp. 2, 480 barrows (BW = 26.3 ± 0.14 kg) were used in a completely randomized design (60 pens; 15 replications) with the following treatments: (1) unmedicated CON diet, (2) 15 mg/kg narasin (0 to 91 d; NAR-91d), (3) CON (0 to 56 d) followed by 15 mg/kg narasin fed from 56 to 91 d (NAR-35d), or (4) 27.6 mg/kg zinc bacitracin (0 to 91 d; ZB-91d). In Exp. 3, 416 barrows and gilts (BW = 84.3 ± 0.39 kg) were used in a randomized complete block design (52 pens; 26 replications) with 35-d treatments: (1) unmedicated CON diet or (2) NAR-35d.

Results and Discussion

In Exp. 1, pigs fed NAR-90d had greater BW (d 90) and ADG (d 0 to 90) compared with pigs fed the CON dietary treatment. The ADG of pigs fed NAR-90d were greater than those of pigs fed the CON treatment on d 0 to 28 and d 28 to 56 and VIR-90 on d 0 to 28. Pigs fed NAR-90d had greater hot carcass weights and yields than those fed CON or VIR-90d. In Exp. 2, pigs fed NAR-91d (d 0 to 56) and pigs fed NAR-35d (d 56 to 91) had greater ADG and ADFI than any of the other treatments. In Exp. 3, pigs fed NAR-35d had greater G:F than pigs fed the CON treatment.

Implications and Applications

Pigs fed narasin tended to have greater growth performance responses in the periods after first receiving narasin. However, when narasin is fed for the entire growing-finishing period, pigs may have carcass responses in some cases. Improvements in growth performance were realized whether narasin was initiated in the early grower or finishing phase.