Performance and Internal Parasite Burden of Stocker Steers Treated Continuously with Morantel Tartrate

Abstract

Three experiments were conducted to evaluate performance and fecal nematode egg counts in grazing stocker cattle receiving morantel tartrate (MT) in two continuously administered forms. In Exp. 1, 80 crossbred steers either received no anthelmintic (C) or were dewormed at the initiation of a 140-d bermudagrass grazing study with either levamisole injection (L) or MT in a sustained-release trilaminate (MSRT). Anthelmintics did not affect performance parameters, but fecal nematode egg counts were lowest from L, intermediate from MSRT, and highest from C at the end of the study. In Exp. 2, 60 crossbred steers grazing fall-regrowth smooth bromegrass were offered a mineral mixture of trace-mineralized salt and dicalcium phosphate (3:1 ratio) with 0 or 10% dried molasses and 0 or 5.58 mg/g MT. Steer gains were similar (P>.10) across treatments, but fecal egg counts were reduced (P<.05) by MT. In Exp. 3, 120 crossbred steers grazing smooth bromegrass pastures were used in an experiment with a 2 x 2 factorial arrangement of treatments to evaluate the effects of grazing intensity and 5.58 mg/g MT in a mineral mixture. Steers grazing at the highest stocking rate (3.7 steers/ha) had reduced (P<.01) gains but improved (P<.01) gain/ha compared with those grazing at the lower rate (2.5 steers/ha). Morantel tartrate reduced (P<.01) fecal nematode egg counts but had no effect on animal performance at either stocking rate. Morantel tartrate was effective in reducing fecal egg counts, but parasite burden in control animals in all three experiments was not sufficient to reduce animal performance.