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Cooperia study shows ineffective dewormers’ costly effects

Harold Newcomb Published on 24 April 2012
Cooperia infections appear to induce a marked change in the intestinal wall of the small intestine

The parasite Cooperia has become the most prevalent internal parasite in U.S. cattle operations, according to research data from USDA’s National Animal Health Monitoring Service (NAHMS) Beef 2007 to 2008 cow-calf survey.

Although its prevalence has been studied, the economic impact of Cooperia on cattle productivity has not.

Findings from a newly published research study completed by leading U.S. parasitologists and sponsored by Merck Animal Health now bring to light the negative impact Cooperia has on productivity if a deworming program is ineffective.

The study demonstrated Cooperia does, indeed, have a harmful effect on both appetite and average daily gain (ADG).

Calves infected with Cooperia gained 7.4 percent less weight than non-infected calves, gaining 3.00 pounds per day vs. 3.24 pounds per day.

The infected animals also consumed 1.5 pounds per day less on a dry matter basis compared to non-infected cattle.

New enemy number one

As part of the 2008 NAHMS cow-calf study, researchers at USDA’s Ag Research Service sought to identify animals harboring internal parasites and determine what parasites actually were present and still shedding eggs after treatment with common dewormers.

Using DNA-screening methods, researchers found two out of every three herds showing poor efficacy contained Cooperia (small intestinal worms) after deworming.

For decades, the brown stomach worm – Ostertagia (O. ostertagi) – was believed to be the most pathogenic and economically costly of cattle gastrointestinal parasites.

To their credit, avermectin dewormers have done a good job of controlling these performance-robbing parasites. But, over time, the constant removal of the brown stomach worm favored the colonization, proliferation and retention of Cooperia.

On-feed study

The in-depth study of Cooperia was initiated in the fall of 2009, when 200 calves with an average weight of 460 pounds were acquired from northwestern Arkansas and northeastern Oklahoma.

Upon arrival, all animals 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 feedbunks. 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 drenched orally 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.

Table 1: Prevalence of diseases

Data collected included biweekly fecal egg counts, daily individual feed consumption and weight gain during 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. The presence of Cooperia punctata (greater than 98 percent) was later confirmed by necropsy on days 35 and 60 post-infection.

Should Cooperia matter to you?

Data from the peer-reviewed study suggested Cooperia punctata has a negative impact on both appetite and ADG.

The infected group gained 7.4 percent less weight (p=0.02) than the non-infected animals, showing an ADG of 3.0 pounds vs. 3.24 pounds. The infected animals also consumed 1.5 pounds less per head per day on a dry matter basis compared to non-infected cattle (p = 0.02).

To put the results into perspective, compare the effects of Cooperia infection to other attributes of production in the feedlot. 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 ADG by more than 7 percent and diminish, if not nullify, the benefit of your implant program during the first 60 days.

Animals infected with Cooperia punctata 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 less pounds of feed per head per day means less feed sold and less gain for the feedlot 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. Cooperia-infected animals gained 0.24 pounds less per head per day. This means that same 100-head pen of cattle gained 1,440 less pounds during the 60-day trial.

Impacting immune response

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

Necropsies performed on days 35 and 60 after infection with Cooperia larvae revealed considerably swollen mesenteric lymph nodes. Swollen lymph nodes indicate a powerful TH2 immune response to parasite infection.

The immune system can become hyperstimulated and go into overdrive. The result is the suppression of TH1 immune responses that are needed to fight off viruses and develop protective immunity from your vaccination programs. So high levels of Cooperia also 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.

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).

Figure 1: resistance in macrocyclic lactones

Fecal egg counts were performed on the day of deworming (day 60) and 14 days later (day 74). The Fecal Egg Count Reduction Tests (FECRT) determines 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.

An effective parasite control program is important to all types of cattle operations. Work with your veterinarian or animal-health provider to do fecal egg count reduction tests and to ensure your herd is protected against the U.S. cattle industry’s most prevalent internal parasite – Cooperia.  end_mark

Harold Newcomb is a technical services veterinarian and lives in Mississippi and can be contacted at (662) 609-6364.

PHOTO

Infections appear to induce a marked change in the intestinal wall of the small intestine Photo courtesy of Merck Animal Health.

harold newcomb

Harold Newcomb

Technical Services Specialist
Merck Animal Health

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