The ability of producers to estimate the live bodyweight of cattle can critically affect whether animals receive too little drug or too much, which can have a significant impact on herd health and ultimately, on the profitability of a producer’s operation. And given that the weight of mature cows has increased by more than 300 pounds during the past 30 years, the potential for under- or overdosing poses a real health and financial risk for any operation that estimates cattle weight.
Proper dosing is especially important when it comes to parasite control. With inadequate or no parasite control programs in place, the cost to producers can be as much as $200 per head, per grazing season. Producers simply can’t take chances when it comes to properly administering parasite control products.
One method often used is simply looking at an animal, estimating its weight based on appearance and dosing accordingly. This method, however, is not reliable, as it has been shown that cattle weights are often underestimated. Results of a study showed the actual weight of 85.7 percent of the evaluated cattle was underestimated by an average of 46.9 percent.4 In the same study, only 19 percent of the cattle weights were estimated within +/-20 percent of their true weights. Findings such as these raise concerns that the estimation of cattle weight can result in considerable drug underdosing.
Another method commonly used is evaluating a group of cattle and estimating the average weight of the group and then dosing according to that weight. This is known as the "Set it and Forget it Method." As a result, some animals in the group are properly dosed, while lighter-weight animals are overdosed and heavier-weight animals in the group are underdosed.
Ray Kaplan, DVM, Ph.D., DEVPC, professor of parasitology at the University of Georgia, says the best technique to guarantee proper dosing is to purchase a scale. "Individually dosing animals to their actual weight can lead to more effective parasite control," Kaplan says. "Scales today can be very reasonable to purchase. In addition, having a scale to take individual animals weights opens the door for other management practices like culling dams based on calve weaning weights."