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Evaluation of long-acting eprinomectin and a combination of moxidectin/oxfendazole administration post-weaning on immune status by Angus and Angus × Hereford crossbred replacement heifers over a 274-d grazing period
Internal parasite burdens have been reported to decrease animal performance and feed efficiency; however, little current research has evaluated the effects of burdens on the immune status in beef cattle. The objective of this study was to evaluate the effects of anthelmintic therapy on the immune status in replacement crossbred beef heifers. Beginning June 2, 2014, 83 fall-born Angus and Angus × Hereford replacement heifers were stratified by d -14 BW and fecal egg counts, and d of age. Heifers were then allocated randomly to 1 of 3 anthelmintic treatments consisting of: 1) control (n = 28; no anthelmintic administered; CON); 2) moxidectin/oxfendazole combination (n = 28; MO); or 3) long-acting eprinomectin (n = 27; LAE) for a 274-d grazing study. Heifers grazed in individual treatment groups on pastures, containing predominantly endophyte-infected tall fescue, for the duration of the project and were supplemented daily at 1% BW with corn gluten. Whole blood was collected via jugular vein on d 0, 14, 28, 84, 154, 168, 182, 234, and 274. On each d complete blood cell differentials were determined using a Cell-Dyn 3700 SL machine. Data were analyzed using the PROC MIXED of SAS for repeated measures. Two orthogonal contrasts were used and included: 1) comparing the mean of CON vs the mean of treated heifers; and 2) comparing the mean of MO vs LAE. Concentrations of white blood cells (WBC), lymphocytes, eosinophils, basophils, red blood cells (RBC), and platelets were greater (P ≤ 0.02) from CON compared with treated heifers. The neutrophil:lymphocyte ratio (NEU:LYM) was greater (P < 0.01) from treated heifers compared with CON, and basophils were greater (P = 0.01) from MO compared with LAE; however, proportions of neutrophils and monocytes did not differ (P ≥ 0.54) amongst treatments. A d effect was detected (P <0.01) for WBC, lymphocytes, and monocytes. A treatment × d interaction (P ≤ 0.01) was detected for neutrophils, NEU:LYM, eosinophils, basophils, and platelets. A treatment × d tendency (P = 0.08) was detected for RBC, with RBC being highest for all cattle on d 0 and lowest on d 234 for LAE. Based on this study, anthelmintic therapy may positively impact immune status in replacement beef heifers treated with various anthelmintics.
Keywords: immune status, immune status, long-acting eprinomectin, moxidectin/oxfendazole combination,