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Although liver flukes are known to cause condemned livers, research concludes that liver flukes may impact cattle in ways not obvious to the USDA inspector -- and that's in the area of performance. " It definitely pays to treat cattle infected with liver flukes," says Dr. M.G. Scroggs of Merial, "as long as you treat at the right time. Once they are infected, the liver will probably be condemned, but decreasing the fluke burden will almost always improve production." Dr. Ray Kaplan of the University of Georgia agrees. "If you look at the studies done on liver flukes, the vast majority show a benefit in performance when the animals are treated at the right time." Kaplan cautions that the degree of improvement depends on the class of animal and the extent of the fluke burden. "The larger the burden, the greater impact treatment will have on performance." The improvement in performance can be realized in the areas of replacement heifers as well as yearling cattle. In a 1998 study in Spain, researchers demonstrated that heifers infected with liver flukes reached puberty 39 days after the uninfected control heifers. Additionally, they had abnormal sexual hormone levels when compared to the control. A similar study at Louisiana State University found that replacement heifers treated for gastrointestinal nematodes and liver flukes had first-service pregnancy rates 23 percent higher than the heifers not treated. 
Effects on the productivity of steers on pasture and the feedlot were mixed. The study, published in Agri-Practice and conducted by Sara Marley, et. al., found no significant differences in performance data in fluke infected steers versus non-infected groups during the grazing phase of the study. However, during this phase, the flukes were immature -- less than 10 weeks old -- which is too young to be affected by most flukicide products. Once the steers entered the feedlots, the steers that were treated with a flukicide demonstrated 28.5 pounds of additional weight gain, which is equal to an adjusted average daily gain of 0.23 pounds. Dr. Jack Malone, a veterinary parasitologist at Louisiana State University, believes backgrounders can benefit the most from treatment. "Typically, the largest majority of cattle in the south are backgrounded in the fall, which is when the flukes start to mature. During the growing and egg laying phases are when the flukes are at their most pathogenic phase," he says. "Then consider the increased stress cattle undergo at the beginning of the backgrounding period. Decreasing the fluke burden during that time gives the calves a chance to grow without suffering additional fluke-related stress." As the flukes get older -- past the egg laying stage -- cattle begin shedding the flukes naturally, Malone explains. "The longer you wait after the mature phase, or about 12 weeks, the less and less flukes will affect the cattle." In the south, there is a two-month time period when fluke burdens are the highest, and treating during that time is beneficial, he says. 
Dr. Rob Rew, managing technical services parasitologist of Pfizer Animal Health, believes treating cow herds for flukes is the best way to maximize performance in fluke-infected areas. "By strategically treating cow/calf herds for flukes, producers can raise larger numbers of 'never infected' calves. That increases the odds that their calves will be good performers at all stages of the production chain, and producers will see fewer condemned livers." |
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