Research Summary - 3
Targeted deworming to promote fecal pat degradation and limit anthelmintic resistance in an intensive rotational grazing system
| Date/Time: |
9/13/2025
09:15
|
| Author: |
Abby Dies |
| Clinic: |
Iowa State University |
| City, State, ZIP: |
Ames, IA 50010 |
Abby Dies, BS 2026
1
;
Dr. Grant Newell, DVM, MS, PhD
1
;
Dr. Megan Hindman, DVM, MS
1
;
1Veterinary Diagnostic & Production Animal Medicine, Iowa State University, Ames, Iowa, 50014
Introduction:
Anthelmintics, specifically macrocyclic lactones, are commonly used in cattle operations to control internal and external parasites. Continuous use of these drugs creates parasitic resistance, which is often undetectable in beef cattle until late in the disease cycle, causing a need for targeted deworming treatment. Overuse of anthelmintics poses many adverse consequences including anthelmintic resistance and the reduction of dung beetle populations. Dung beetles are crucial to maintaining healthy pastures in intense rotational grazing systems due to their ability to quickly degrade fecal pats, and promote forage regrowth, both of which reduce opportunities for parasitic reproduction. This study evaluates the impact of a targeted deworming program over a two-year period and their effects on pasture dung beetle population, the overall parasite load in a commercial cow herd, as well as the impact of production parameters on the calves.
Materials and methods:
This study took place on a commercial angus cow-calf operation in south central Iowa. The data collected was for the first year of a two-year study. Two groups were administered a targeted deworming treatment. Three-year-old (n=45) and young cows, ages 4-7 years (n=70) were individually weighed and treated with 1 mL/10 kg of Doramectin. Two positive control groups old cows ages 7-13 years (n=110) and two-year-old cows (n=47) were also weighed but not treated with anthelmintic. Ten random fecal samples were taken from the pasture group and fecal egg counts were analyzed using the Modified Wisconsin McMasters protocol. Five dung beetle pitfall traps were placed in a dice pattern in each pasture and collected weekly to measure the dung beetle populations. In addition, a single fecal pat per pasture was sampled to calculate dry matter percentage to capture fecal degradation. Cages were placed around each fecal pat to ensure its protection. All cows also received diflubenzuron in lose mineral form at least two-weeks prior to the start of the trial and throughout the grazing period. Statistical analysis was completed using the R program (R Core Team, 2016). The alpha was set at 0.05.
Results:
Fecal egg counts showed that all groups except the three-year-old cows had low or rare Strongyle counts. Capillaria counts were disregarded as it was said to have no specific pathogenicity to cattle. The average dung beetle count throughout the study period for year one for the treated groups of two-year-old and young cows were 151 and 303.75 respectively. The average dung beetle count for the non-treated groups, three-year-olds and old cows were 412 and 154 respectively. The average daily gain (ADG) and weaning weight of treated female calves (P=0.0134 and P=0.0427, respectively) was greater than the ADG and weaning weight of non-treated calves. The treated two-year-old and young females showed an ADG of 1.03 kg/day and 1.02 kg/day respectively. The non-treated three-year-old and old female calves showed an ADG of 0.98 kg/day. Fecal dry matter percentages by pasture increased weekly, indicating ongoing fecal degradation.
Significance:
The treatments did not differ statistically between collection intervals, nor did it differ statically in male calves for both weight and ADG. Additionally, dung beetle counts did not reflect decreasing amounts with the treatment protocols. Furthermore, the dry matter percentage did not differ between treatment groups. The study showed a small statistical difference in female calves for weaning weight and average daily gain. Year one of this study did not show statistically significant differences in dung beetle populations in treated and non-treated pastures, possibly due to lower beetle populations in different pastures. However, the study did indicate the treatment had a significant impact on the ADG for female calves. Repetition of the study is warranted to validate these findings and investigate further the effects of anthelmintics on parasite counts and herd productivity.
