Abstract Gastrointestinal nematode (GIN) parasites pose a significant health concern for beef cattle producers in North Carolina, where the warm, humid climate supports year-round parasite survival and transmission. Calves are particularly vulnerable at weaning, a period of high stress when fecal egg counts (FEC) often peak due to immature immunity and increased physiological demands. The objective of this study was to evaluate the effects of deworming timing before or at weaning on calf health and performance. A total of 90 Angus-based calves (steers: n = 52, and heifers: n = 38; average 7 mo) were randomly assigned to two treatment groups: (1) administration of Dectomax® according to label directions at pre-weaning vaccination (∼4 weeks before weaning, d14) or (2) administration at weaning (d42). Body weight (BW), body condition score (BCS), FEC, and average daily gain (ADG) were collected every 14d from d42 pre-weaning (d0) through d28 post-weaning (d70). The FEC was determined using a Modified McMaster’s procedure with a triple-chamber slide and reported as eggs per gram (EPG). Data were analyzed in SAS (PROC MIXED), with significance defined as P ≤ 0.05 and trends at 0.05 P 0.10. The BW increased across the study period for all calves (P 0.001), with steers consistently weighing more than heifers (158 vs. 144 kg, respectively). Steers also maintained higher BCS than heifers (4.4 vs. 4.2, respectively, P 0.01). Treatment timing had no effect on BW (P 0.10) or BCS (P 0.10). The FEC tended to decrease after deworming in both groups (100 vs 150 EPG decrease for pre-wean and at wean deworming in 14d post-deworming), but no treatment effect was detected (P 0.10). Unexpectedly, only 25% of calves achieved ≥90% fecal egg count reduction (FECRT) within 14d post-treatment, below the industry benchmark. Further investigation is needed to determine if there is reduced efficacy of Dectomax® in this herd. The ADG followed standard growth trends but was not different (P 0.10) between treatment groups. Deworming at pre-weaning vaccination may provide slight advantages by reducing parasite exposure during a lower-stress period, but overall timing of Dectomax® administration did not alter performance outcomes in this study. Evidence of suboptimal FEC reduction highlights the need for FECRT, exploration of alternative anthelmintic protocols, and integrated parasite management approaches.
Dudley et al. (Wed,) studied this question.