Five deworming trials were conducted at the Eastern Research Station located near Haskell, Oklahoma during the 1990’s. Crossbred cows and their Charolais sired calves were sorted by sex of calf, calf age and cow age, then randomly allotted to one of four treatments: 1) non-dewormed control, 2) deworm calf only; 3) deworm cow only; and 4) deworm cow and calf. Two or three treatments were applied each year including one control group. Each treatment was applied two or three years. Cows and calves were individually identified and weighed in early June. Treated animals received label-recommended dosages of a commercially available pour-on. Pairs grazed in rotation seven bermudagrass pastures overseeded with clover at a stocking rate of 2 acres per cow-calf pair during the 144 to 181-day trials. Initial studies indicated that a low worm infection rate was present in the first two years. At that time fecal egg counts ranged from 0 to 28 eggs per 3 gram sample of feces.
Deworming cows in late spring had no significant effect on cow summer weight gains up until calf weaning time. Treating cows but not their calves resulted in a small advantage in average daily calf weight gains (0.1 pound/day); while treated spring-born calves had significantly greater daily weight gains (0.14 pound/day) while nursing non-treated cows. In other words, just deworming the calves resulted in a 21 pound weaning weight advantage over non-treated controls. Treated calves nursing treated cows had significantly greater average daily weight gains (0.17 pound/day) than the untreated calves nursing untreated cows. Over the approximate 150 day period this weight gain advantage would total about 25 pounds additional weaning weight to calves in this treatment group. In this series of studies, deworming spring-born nursing calves in early summer resulted in summer weight gains of 21 pounds. Deworming both cow and calf resulted in an increased summer weight gain of 25 pounds versus non-treated controls (or 4 pounds more than when the calf alone was treated.)
In these studies, reproductive performance was quite high for both treated and non-treated cows, and no difference was noted. Different results may occur in different climates and under different stocking rates. In 2013, with some thin cows going out on short, overgrazed pastures, deworming the cow may have a greater impact on cow performance.