United States Department of Agriculture • Animal and Plant Health Inspection Service • Safeguarding American Agriculture 

Veterinary Services 

Centers for Epidemiology and Animal Health December 2009 

_________________________________________________________________________________________________________________________ 

Parasites on U.S. Beef Cow-calf 

Operations, 2007–08 

Internal parasites can reduce the reproductive 

performance of the cow herd, reduce weaning weights of 

calves, and negatively impact animal health due to 

respiratory disease, immunosuppression, and other 

illnesses. 

The U.S. Department of Agriculture’s National 

Animal Health Monitoring System (NAHMS) conducted 

the Beef 2007–08 study, which focused on beef cow-calf 

health and management practices in 24 States.1

 These 

States represented 79.6 percent of U.S. cow-calf 

operations with beef cows and 87.8 percent of U.S. beef 

cows. One objective of the Beef 2007–08 study was to 

describe the parasite load in weaned beef calves on 

cow-calf operations in the United States. 

Study design and sample testing 

During the Beef 2007–08 study, operations were 

offered the opportunity to participate in two phases of 

fecal testing. Fecal samples were collected from March 

through December 2008. In Phase 1, samples were 

collected from weaned beef calves 6 to 18 months of 

age that had been on pasture for at least 4 weeks and 

had not been dewormed within the previous 45 days. In 

Phase 2, the efficacy of the operations’ current 

deworming programs was evaluated. Operations were 

instructed to deworm all animals in the pasture within 48 

hours after collecting Phase 1 samples, then collect 

samples approximately 14 days after the deworming 

treatment, again from weaned beef calves aged 6 to 18 

months. 

During both phases, 20 fecal samples from weaned 

calves were collected (usually off the ground), bagged, 

and shipped overnight to one of three previously 

designated laboratories.2

 All labs used the Wisconsin 

Double Centrifugation Flotation or the Modified 

Wisconsin techniques. Results were expressed as eggs 

per gram of fecal material (EPG). Parasite eggs were 

 

1 States/Regions: 

West: California, Colorado, Idaho, Montana, New Mexico, Oregon, 

Wyoming 

Central: Iowa, Kansas, Missouri, Nebraska, North Dakota, South 

Dakota 

Southeast: Alabama, Arkansas, Florida, Georgia, Kentucky, 

Louisiana, Mississippi, Oklahoma, Tennessee, Texas, Virginia 

2 Colorado State University, Fort Collins, CO; USDA:ARS, Beltsville, 

MD; University of Minnesota, St. Paul, MN

counted and identified by type (strongyle-type, 

Nematodirus, or Trichuris). Samples were classified as 

positive or negative for tapeworms and for coccidia 

oocysts. 

Phase 1 results 

Of 567 operations, 291 indicated an interest in 

submitting samples for parasite evaluation. Of these, 99 

submitted 1,772 Phase 1 samples that could be 

evaluated and reported. 

 Phase 1 testing found that 85.6 percent of all 

samples submitted were positive for strongyle-type eggs 

(table 1). The West region had the lowest percentage of 

samples positive for strongyle-type eggs (77.5 percent), 

and the Southeast region had the highest percentage 

(89.9 percent). Nematodirus and Trichuris eggs were 

found in 18.0 and 7.1 percent of samples, respectively. 

Table 1. Percentage of Fecal Samples Positive for 

Parasites, by Parasite Type and by Region

Percent Samples 

Region 

Parasite Central Southeast West Total 

Strongyle 87.7 89.9 77.5 85.6 

Nematodirus 19.2 9.7 23.8 18.0 

Trichuris 7.6 7.0 6.3 7.1 

Coccidia 58.0 63.1 60.5 59.9 

Tapeworm 11.9 13.0 17.5 13.7 

The average EPG for strongyle-type eggs ranged 

from 11.3 in the West region to 58.1 in the Southeast 

region (table 2). Samples with zero EPG are included in 

the calculation of average EPG. 

Table 2. Average Eggs per Gram, by Region 

Sample Average EPG

Region 

Parasite Central Southeast West Total 

Strongyle 30.3 58.1 11.3 32.5 

Nematodirus 1.0 0.2 0.9 0.8 

Trichuris 0.2 0.2 0.1 0.1 
United States Department of Agriculture • Animal and Plant Health Inspection Service • Safeguarding American Agriculture 

Phase 2 results 

Phase 2 was conducted to determine the apparent 

effectiveness of current anthelmintic treatment programs 

for reducing the number of parasites (fecal egg counts) 

in U.S. cow-calf operations. A second set of fecal 

samples were collected approximately 14 days after the 

Phase 1 collection and after the animals were dewormed 

using the standard parasite control practices for the 

operation. Sixty-one operations provided usable samples 

for Phase 2. 

 Guidelines suggest that a fecal egg count reduction 

(FECR) test with less than 90 percent reduction 

indicates the presence of anthelmintic resistance (Bliss 

et al., 2008). Operation-level FECR was calculated by 

comparing the mean pretreatment egg count with the 

mean post-treatment egg count. Nearly one of three 

operations showed less than an 80 percent reduction in 

strongyle fecal egg count after treatment (table 3), and 

44.3 percent showed less than a 90 percent reduction in 

strongyle egg count. The less than 90 percent FECR 

could be due to improper or incomplete treatment or 

reduced efficacy of the drugs used. 

Table 3. Fecal Egg Count Reduction Results and Types of Dewormers Used 

 Operations Using Various Types of Dewormers 

Parasite 

Reduction 

Value (%) 

Number 

Operations 

Percent 

Operations

Number 

States 

Brand 

Name 

Pour-on

Generic 

Pour-on

Brand 

Name 

Injectable 

Generic 

Injectable Feed Oral 

Strongyle <80 19 31.2 10 11 (57.9) 8 (42.1) 0 0 0 0 

<90 27 44.3 11 13 (48.2) 12 (44.4) 2 (7.4) 0 0 0 

All 

operations 61 100.0 17 27 (44.3) 16 (26.2) 12 (19.7) 1 (1.6) 3 (4.9) 2 (3.3)

Nematodirus <80 23 57.5 9 7 (30.5) 12 (52.2) 2 (8.7) 1 (4.3) 1 (4.3) 0 

<90 25 62.5 10 8 (32.0) 12 (48.0) 3 (12.0) 1 (4.0) 1 (4.0) 0 

All 

operations 40 100.0 12 17 (42.5) 14 (35.0) 5 (12.5) 1 (2.5) 1 (2.5) 2 (5.0)

Trichuris <80 7 21.9 5 4 (57.1) 2 (28.6) 1 (14.3) 0 0 0 

<90 11 34.4 9 6 (54.5) 2 (18.2) 2 (18.2) 0 1 (9.1) 0 

All 

operations 32 100.0 12 15 (46.9) 10 (31.3) 3 (9.4) 1 (3.1) 1 (3.1) 2 (6.2)

Summary 

Internal parasite populations still have a major 

presence on U.S. beef cow-calf operations. More study 

is necessary to determine the extent of resistance to 

anthelmintic drugs among parasite populations and the 

best ways to ensure the effectiveness of the available 

drugs. 

Reference 

Bliss DH, Moore RD, Kvasnicka WG. Parasite resistance 

in U.S. cattle. American Association of Bovine 

Practitioners 2008; 41:109-114. 

_____________________ 

For more information, contact: 

USDA:APHIS:VS:CEAH 

NRRC Building B, M.S. 2E7 

2150 Centre Avenue 

Fort Collins, CO 80526-8117 

970.494.7000 

E-mail: NAHMS@aphis.usda.gov 

http://nahms.aphis.usda.gov 

#572.1109 

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