The response of cattle on a sorghum-based feedlot diet to monensin supplied either via intraruminal capsules or in the feed

Abstract

A feedlot experiment with Hereford steers of initial liveweight of 249 ¦ SE 3.0 kg was done to investigate the production responses to the addition of monensin either in the feed (30 ppm) or in intraruminal controlled-release capsules (CRC). The ration was 90% concentrate (94.3% sorghum, 3% tallow, 2.7% minerals), 10% cotton seed hulls with the following treatments: (A) control, (B) 30 ppm monensin in feed, (C) 50 mg monensin day-1 CRC, (D) 100 mg day-1 CRC, (E) 200 mg day-1 CRC, and (F) 300 mg day-1 CRC. The dry matter intakes and growth rates of the six groups (A to F) were 7.57 and 1.32; 6.56 and 1 .I 3; 7.60 and 1.35; 7.08 and 1.24; 7.39 and 1.35; and 7.05 and 1.23 kg day-1, respectively, with the dry matter intakes for monensin in feed (B) being lower (P < 0.05) than the remaining treatments, and for the same treatment the growth rates were lower (P < 0.05) than treatments A, C and E. The apparent feed conversion ratios (DMI kg-I LW gain) were 5.75, 5.92, 5.78, 5.86, 5.61 and 5.79, respectively, and did not differ (P > 0.05). Generally, the addition of monensin had no effect on carcase characteristics or on liver abscesses. It was concluded that the addition of tallow to the diet may have altered the rumen fermentation pattern sufficiently to prevent further benefit from the addition of monensin.