Goat Parasites Phase 2

During Phase 2, eggs are deposited on the pasture though the goats’ feces. The extent of pasture contamination during Phase 2 is affected mainly by stocking rate, or the number of animals per grazing area; age of the animals, season of the year and hypobiosis. It is also strongly affected by the species of worm because the females of some worm species such as barber pole worm (Haemonchus contortus) lay far more eggs than other species.

The higher the stocking rate, the more feces are deposited on the grazing area, thus more eggs, leading to more contamination. More eggs are also passed from young versus older animals. Most worms have a definite seasonality, so during their most favorable seasons, more eggs are produced and passed. Of particular note in small ruminants, is a phenomena called the peri-parturient rise (PPR) in fecal egg output. This occurs at or around parturition (kidding or lambing) and extends through most of the lactation period. Because late pregnancy, kidding and lactation are stressful conditions, the dam’s immune system is compromised. Furthermore, nutrients are partitioned preferentially to support mammary and fetal development and then lactation, which also decreases the animals’ ability to generate an effective immune response to worm infection. This allows the existing female worms to increase the number of eggs laid, thus increasing the number of eggs deposited in the feces.

If a worm species undergoes hypobiosis (a period of suspended animation or “hibernation”), the development time to the adult stage can be extended by several months. This will result in fewer adult worms during the dormancy or hypobiosis season and fewer eggs deposited in feces. However, when these hypobiotic larvae resume development, massive numbers become mature adults over a short period of time, and the resulting increase in egg production can be very high leading to sudden increases in pasture contamination.  Additionally, this sudden increase in adult worms can have severe adverse effects on the host goat depending on the feeding patterns of the adult worms.