When is the right time to deworm cattle in 2006?
Short grass is commonly thought of causing wormy cattle by the cattle grazing down where the worms are, but that thought is a misunderstanding. The reason that producers think that way is because the cows look wormy, when actually the cows' poor body and hair coat conditions are related to malnutrition from low intake of roughages on short grass pastures. When short grass is caused from dry conditions due to lack of rain and from overgrazing the slow growth of grass, the worms are not down there in the soil; the larvae have died from the dryness, and also from the heat in the summer.
When stomach worm eggs are passed in cattle manure, the eggs hatch in the manure. The larvae must be washed from the manure by rains. The larvae can only crawl (swim) up the grass blades while the grass is wet from rain or dew. As the grass dries, the larvae go back down to find moisture. As cattle graze dry grass, they don't ingest larvae. After weeks of dry weather, larvae die, and without grass mats for cover, all the larvae die, and the pastures become free of contamination.
While pastures are contaminated with larvae, it may be cost effective to worm if the cattle have become exposed to enough larvae during 3 6 weeks of continuous rains with soil temperatures of 55 85 degrees when the larvae are active. If these conditions occur in the spring on some pastures; the timing to worm the cattle is following 3 6 weeks of continuous rain. If the rains come on contaminated pastures, that would make deworming cattle in May but not all pastures are contaminated because of the drought and good management practices. With rains in a cold April, the larvae hibernate and there is no exposure until May, to make worming in June. If rains don't come, cost effectiveness of deworming cattle in the spring is questioned, as it was in the fall and lspring of 2005. When worming is cost effective, it's in the nursing calves and young cattle and possibly not in the cows and bulls.
Adult stomach worms live for about 2 months and die of old age, and their larvae are transmitted only during moderate temperatures and wet conditions. Since cattle do not have stomach worms throughout the year, determining the proper timing for worming cattle when they have worms is critical; if they are not there, do not deworm. Don't look at the cows, look at the ground...any wet grass over a period of weeks?
When it is dry in the spring and fall, do not deworm; wait until the cattle get the worms, which may or may not come this year. The spotty rains this year may be an indication that it is coming for some. But for the last 10 years, that hasn't been for many places.
EPG fecals do have place to evaluate and monitor deworming and management practices and determine to maintain or change the control program but not to determine to whether or not to deworm. Adult stomach worms' presence can be found by EPG fecals but since they are not harmful, deworming based on fecals is too late, because the damage is caused earlier by the emergence of larvae. The key is to time the deworming during recent spring or fall optimal transmission when larvae are developing or during summer inhibition before the larvae emerge. EPGs fecals every month are helpful to determine a pattern of transmission. When the timing is right for deworming, the cost-effectiveness is expected in nursing calves since they are more susceptible but is not always expected in adults since they are more resistant.
