Nursing calves often do not support significant worm burdens due to lack of grazing behavior. The animals most susceptible to the effects of internal parasites are weaned young animals such as replacement heifers and stocker calves. Thin animals tend to be more likely to suffer from the effects of intestinal parasites. These animals are also more likely to benefit from deworming and other kinds of parasite control. Population density is the number of animals per acre.
Animals tend to avoid grazing where manure is in pasture.
While less densely populated pastures may make poor use of forage, parasite transmission is reduced. Cattle grazing short pastures are more likely to graze where manure is. Also, parasite larvae are more likely to be found on the lower parts of pasture plants which cattle must graze in short grass conditions. Stored feeds such as hay normally do not hold parasite larvae and transmission of parasites is less likely to occur. Also, animals housed in barns, on drylots, or in feedlots do not contact a lot of worm larvae.