Goat Parasites Phase 4

Goats November 03, 2015 Print Friendly and PDF

The infectious stage, Phase 4, is affected by stocking rate in two ways. If the same animals are still grazing the pasture, the stocking rate determines how many eggs initially contaminated (Phase 2) the pasture and, consequently, how many infective larvae were available from the feces initially deposited to infect the animals that are still grazing in the same pasture at the same stocking rate. Often it is advisable to remove the animals from a grazing pasture before the eggs from their feces have had a chance to mature into infectious larvae to infect the animals again.  This reinfection from feces deposited during the current grazing period is called autoinfection

If the initial contaminating animals are removed and replaced by new animals, the new stocking rate will influence the level of exposure each animal has to infective larvae during grazing, that is, the higher the stocking rate, the more chance of exposure and vice versa. However, the species of worm with regard to its egg laying ability also strongly influences the level of contamination of a pasture. The period of time a pasture has been rested also affects the level of contamination.  In the tropics, the population of barber pole infectious larvae peaks at about 14 days after fecal deposition and starts to drop substantially by 30 days after fecal deposition. In contrast, barber pole infectious larvae peak at about 28 to 35 days after fecal deposition in temperate climates and do not start to drop appeciatively until about 60 days after fecal deposition.Humidity and temperature strongly affect the survivability of these populations.

It is well known that grazing animals prefer not to graze close to feces. Thus, the farther away they are from fecal deposits, the less their chances of being exposed. However, eventually the feces disintegrate, forage grows well with the fertilization, and animals will graze over the area where exposure was initially very high. Natural sources of water, such as streams, ponds or lakes, provide moisture along the banks where forage can grow readily. When animals congregate to drink and consume the attractive forage, defecation in these areas can lead to increased contamination and eventually more infective larvae. The same can be said for areas where supplements, especially hay, are fed on the ground if conditions are right for development and survival of the free-living stages. Similarly, trees provide an area for animal congregation and shade for larval survival. Small pastures or barnyards that border your barns, shelters, or your watering/feeding areas will also have high levels of fecal contamination and can act as a primary source of worm contamination if they have sufficeint vegetation in them for goats to graze. Under all the above situations, a high-stocking rate has been artificially created in a relatively small area where forage is kept closely grazed and fecal contamination is high.