Dairy cattle behavior and appearance often make it easy to detect external parasites like flies, mange and lice. Severe internal parasite infiltrations can result in roughness of hair coat, anemia, edema and diarrhea. However, the subclinical impact of internal parasites is largely hidden, yet costly. According to a recent study at Iowa State University, undetected subclinical disease caused by internal parasites can cost $190 per animal.
    The greatest impact internal parasites have is generally reduced feed intake. This means animals receive less essential nutrients, including protein, energy, minerals and vitamins. The damage done by internal parasites to the gastrointestinal tract can also reduce absorption of these nutrients critical to cattle health and well being.
    Strategic deworming in growing heifers improves weight gain and overall performance. Calves under 1 year of age are more susceptible than older cattle. Older cattle have been frequently exposed to the parasites and develop a degree of resistance.
    The lifecycle of internal parasites in young heifers is three to four weeks. The general recommendation is to deworm at least once during the summer and in late fall. Assuming this fall treatment occurs after a hard frost, heifers do not need to be treated at spring turnout. Late-fall deworming kills the internal parasites and heifers should not be at risk for re-exposure in the barn during the winter.
    In the lactating dairy cow, the presence of internal parasites results in reduced milk production. Changes in how cows are housed and managed has generally reduced the need to deworm lactating cattle at the same intensity as heifers on pasture.
    The first step in designing a deworming program for lactating dairy cows is to determine the parasite contamination potential. Dairy cattle on rotationally grazed pasture during lactation present the highest risk for internal parasitism. Alternatively, lactating cows on low-density dry lots or in confinement have an extremely low potential for internal parasite infestation. Many herds house their dry cows on dirt lots or pasture where parasite exposure is the highest. Even though the lactating cows are in confinement, they could carry worm loads from the dry period.
    Since dairy cows are most likely to show a positive response during early lactation, the first choice for a deworming program is to treat soon after they freshen. If pre-fresh dry cows are housed in confinement, this may be a logical time to treat as well. By removing all the internal parasites during the pre-fresh period, the cow will be better able to handle stress associated with transition and early lactation. Transition group deworming also provides a safety net for heifers entering the herd and ensures that parasites will not affect milk production, growth or reproduction.
    A variety of products are available for control of internal parasites. Pour-on and feed-grade additives are the most commonly used deworming products for dairy cattle. Note that certain products are approved for dairy heifers, but not for adult cattle. Work with your veterinarian and herd health advisors to determine which products fit the needs of your dairy. Implementing an effective parasite control program will allow your herd to maintain optimal health status and maximize performance.
    Barry Visser is a nutritionist for Vita Plus.