Saturday, May 21, 2016

Sheep With a Purpose

Sheep are brought to the test site to graze down the early spring growth and to contaminate the cool season grass pastures with infective worm larvae. They are also brought in after the end of the test to graze the left over forage and eat the fall growing plants.

The sheep play an integral part in ensuring that the test goats face a sufficient parasite challenge. It's not possible to identify resistant and resilient bucks unless there is a sufficient worm challenge. It's not always pretty, but it's the only way to do it. High fecal egg counts are a goal of the test. Resistant bucks will maintain low egg counts (< 1000 epg, some < 500 epg) throughout the test period. Resilient bucks will have FAMACHA© scores of 1 or 2 and will not require deworming.

Three years ago, a DrenchRite® test was performed to determine which anthelmintics (dewormers) were effective against the parasites infecting the sheep.  The test showed the worm larvae (mostly Haemonchus contortus) to be susceptible to moxidectin (Cydectin®) and levamisole (Prohibit®), but NOT the benzimidazoles (fenbendazole/SafeGuard® and albendazole/Valbazen®). For this reason, clinically parasitized goats are only dewormed with Cydectin® or Prohibit® (at dosages recommended by the ACSRPC).

It's time to repeat the DrenchRite® test. Instead of doing the test with fecal matter from the sheep, fecal matter from the test goats will be submitted for testing. A pooled sampled will be collected from the goats after they have been grazing the test site for a month or so. All sheep and goat farms should test for anthelmintic resistance every 2-3 years. The DrenchRite® test is the most practical means to do so, though fecal egg count reduction tests can also be performed.