New enemy No. 1

As part of the 2008 National Animal Health Monitoring Service’s (NAHMS) cow-calf study, USDA-ARS researchers sought to not only identify animals harboring internal parasites, but also get an indication of which parasites were actually present and still shedding eggs after treatment with common dewormers.

“Using DNA-screening methods, we identified which parasites were left behind in the cattle groups with less-than-effective dewormer treatments. In two out of every three herds showing poor efficacy, only certain worms were left behind,” said Bert Stromberg, Ph.D., professor of parasitology at the University of Minnesota. “A large portion of the animal groups with low efficacy contained Cooperia (small intestinal worms) after deworming, which would be indicative of tolerance to a particular anthelmintic treatment by that parasite.”

For decades, the brown stomach worm – Ostertagia (O. ostertagi) – was believed to be the most pathogenic and economically costly of cattle gastrointestinal parasites, explains Stromberg. And to their credit, avermectin dewormers have done a good job of controlling these performance-robbing parasites.

“But over time, the constant removal of drug sensitive and highly immunogenic species such as Ostertagi was favoring the colonization and retention of less immunogenic but avermectin-resistant genera such as Cooperia punctata,” said Stromberg.

“The effect of Cooperia on cattle productivity was largely unknown. It was long considered a non-factor,” explained Lou Gasbarre, parasitology consultant and former research lead from USDA’s ARS Bovine Functional Genomics Lab in Beltsville, Massachusetts. “This study was conducted to look specifically at the impact of Cooperia on cattle productivity.”

On-feed study

In the fall of 2009, 200 calves with an average weight of 460 pounds were acquired from Northwestern Arkansas and Northeastern Oklahoma and, upon arrival, were vaccinated and drenched with fenbendazole and given levamisole according to label directions. Animals were preconditioned for approximately one month and fed a standard growing ration. At four weeks, all calves were dewormed through their feed using fenbendazole, re-vaccinated, and moved to pens equipped with GrowSafe system feed bunks. After an additional week to get acclimated, calves were randomly divided into two groups of 80, and each group was further divided into two replicate pens of 40 calves.

On day 0 and day 14 of the data collection phase, two pens were orally drenched with Cooperia punctata infective larvae. The two control pens received a drench of tap water. To mimic natural infection, researchers sought to infect animals so that, on average, animals carried between 15,000 and 30,000 worms. The presence of Cooperia punctata (>98 percent) was later confirmed by necropsy on days 35 and 60 post infection.

“We’ve infected a couple thousand calves with a bolus infection like this doing research over the years, and we found that larva uptake averages only 10 percent to 20 percent,” noted Gasbarre. “Therefore, we orally drenched each animal in the infected group with 100,000 larvae and then 90,000 larvae resulting in approximately 20,000 to 30,000 parasites in each infected animal.”

Data collected included biweekly fecal egg counts, daily individual feed consumption and weight gain over the 60-day test period. Egg counts were positive by day 14 post-infection and remained at levels similar to those seen in previous field studies.

Do Cooperia matter to you?

Data suggested that Cooperia punctata has a negative impact on both appetite and nutrient uptake. The non-infected group gained weight 7.4 percent more rapidly (p=0.02) than did the infected animals, showing an average daily gain (ADG) of 3.24 pounds versus 3.0 pounds. The infected animals also consumed 1.5 pounds per day less per head on a dry matter basis compared to non-infected cattle (p = 0.02).

“The results are significant. To put them into perspective, compare this impact to other attributes of production in the feedlot,” said Harold Newcomb, technical service veterinarian for Merck Animal Health who observed the research throughout. “Consider that growth-promoting implants increase rate of gain between 8 and 15 percent. Most cattlemen wouldn’t give up the performance advantages implants provide. But, using a dewormer that leaves Cooperia behind could reduce average daily gain by more than 7 percent and diminished, if not nullify, the benefit of your implant program during the first 60 days.”

Animals infected with Cooperiapunctata also eat less as the research showed, providing less fuel for growth and lowering efficiency. Consider a custom feeder selling tons of feed. Calves consuming 1.5 pounds less feed per day (DMI) means less feed sold and less gain for the customer. For a typical 100 head pen, that’s 150 fewer pounds of feed per day. Multiply that over an equivalent 60-day period and that’s 4.5 tons less feed going into those cattle. And with infected animals giving up an average of 0.24 pounds of gain per day, that 100-head pen of cattle equates to 1,440 pounds of unrealized gain.

While we often think of internal parasites harming the digestive track and affecting ADG or feed conversion, an animal’s immune response to parasite infection can also play an important role in the downward spiral of reduced health and increased morbidity.

Gasbarre, who spent much of his career studying cattle immunology, noted that necropsies performed on days 35 and 60 after infection with Cooperia larvae revealed considerably swollen lymph nodes. Swollen lymph nodes, Gasbarre explained, indicates a powerful T_H2 immune response to parasite infection. The immune system can become hyper-stimulated and go into over-drive. The result is the suppression of T_H1 immune responses that are needed to fight off viruses and develop protective immunity from your vaccination programs. So, high levels of Cooperia could impact the effectiveness of a vaccination program.

Necropsies also revealed thickening of the intestinal wall and significant mucus production.  “It was easy to see the digestive systems of infected calves were focused on ridding themselves of an invader rather than absorption of nutrients for growth,” said Newcomb.

Follow-up efficacy tests

At the termination of the production study, the Cooperia-infected group was split into two groups to evaluate efficacy of deworming protocols. The calves were dewormed with two different classes of anthelmintics. One pen was dewormed with an injectable endectocide (Dectomax®) and one pen with a benzimidazole drench (Safe Guard®). Fecal counts were performed on the day of deworming (day 60) and 14 days later (at day 74). These Fecal Egg Count Reduction Tests (FECRT) determined whether the anthelmintic treatment kills the worms in an animal, eliminating the production and shedding of eggs. Efficacy is evaluated as a percent reduction in the average number of eggs per gram from the first FECRT to the second test 14 days later.

Treatment of infected calves with the endectocide did not remove the Cooperia parasites as demonstrated by FECRT results that showed an 8.8 percent reduction in average egg counts 14 days after treatment. Meanwhile, treatment with a benzimidazole was shown to be very effective against Cooperia as the second group of infected calves treated with Safe-Guard showed a 98.1 percent reduction in egg counts 14 days after treatment.

To verify egg count results, necropsies were performed on three animals from each treatment group. Researchers found an average of 24,600 Cooperia worms in the small intestine of the endectocide-treated animals, and only 167 in the small intestine of the benzimidazole-treated calves.