860
Comparison of ivermectin and extended-release eprinomectin deworming treatment on stocker and subsequent feedlot performance and carcass characteristics of fall-born Angus heifers
The objective of this study was to compare the effects of ivermectin and extended-release eprinomectin on stocker and feedlot performance as well as carcass characteristics. Sixty purebred, fall-born Angus heifers (277 ± 23 kg BW; 4.90 ± 0.34 BCS) were blocked by BCS, and BW, and allotted to 1 of 2 injectable deworming treatments after 35 d of grazing summer pasture: 1) ivermectin (Ivomec™; IVO), or 2) extended-release eprinomectin (LongRange™; LR). Concurrent fecal samples were taken at treatment initiation. Heifers were placed back on the same pasture until the pasture was no longer suitable for grazing (total of 63 d). Interim BW was taken 27 d after treatment initiation; and fecal samples, BW, and BCS were taken at grazing termination. At grazing termination, heifers were transported to a feedlot where they remained commingled and fed a finishing ration for 150 d. Upon arrival, heifers were stratified by BW within grazing treatment and allotted to either receive (Ivomec™; DWRM), or not receive a deworming treatment at processing (NO). Fecal samples were collected 4 d prior to transport for slaughter. Carcass data were collect by the Tri-County Steer Carcass Futurity. Binary and continuous data were analyzed using the GLIMMIX and MIXED procedures of SAS, respectively. Heifer BW and BCS did not differ between treatments throughout the grazing period (P ≥ 0.67). Although ADG did not differ during the first 27 d, LR heifers had greater overall ADG and increased BW change (P = 0.01) during the grazing period. Although fecal egg count (FEC) did not differ at treatment initiation, FEC was greater in IVO (5.138 eggs/g) than LR (0.073 eggs/g) heifers at grazing termination (P < 0.01). Final fecal egg counts were nearly undetectable prior to transport to slaughter and did not differ (P ≥ 0.16). There were no differences in feedlot performance or carcass characteristics due to grazing period, feedlot period or the interaction between the 2 treatments (P≥ 0.09). Based on data presented in this study, in cattle that have been effectively managed to reduce or eliminate internal parasite infection during a grazing period, there may be no benefit to deworming at feedlot arrival. However, even at extremely low, subclinical levels of infection during the stocker phase, parasites can have a significant impact on performance. These data highlight the importance of parasite control during the stocker phase, even at subclinical infection levels.
Keywords:
Feedlot, Parasite, Stocker