Left unchecked, this little parasite worm, less than 9mm in length, would be responsible for the greatest productivity loss in grazing cattle in New Zealand. While predominantly affecting young stock during their first winter, Ostertagia is also an issue of older stock.
The vast majority of these worms are present not in the animal, but on the pasture. They develop from eggs passed in cattle dung, from where immature larvae migrate up into the pasture. They are then eaten and migrate to the abomasum (the 4th
stomach) where they burrow into the stomach lining to complete their development to mature adult parasites. It is here, in the abomasums, where most of the damage is done and in large numbers, developing Ostertagia larvae can do enough damage to kill the animal.
Ostertagia larvae also have a unique ability to delay their development in the lining of the stomach, remaining in this ‘inhibited’ state for long periods. Severe disease can result when large numbers of these parasites suddenly develop and cause huge damage to the stomach lining. Called Type II Ostertagiosis, cattle up to 4 years of age and sometimes older are at risk; however young stock in their first winter are once again most at risk.
It is really important to note that not all drench families are effective against inhibited larvae. Levamisole, a product very effective against resistant Cooperia, is an example.
The take-home message is that treating the significant parasites that affect cattle at different times of the year is more complicated than giving them a squirt of whatever you have on the shelf. With the continuing development of resistance to many of our worm drenches, it is important to make the right decision when choosing a product, even if you are only treating a few animals. A few minutes talking to our staff could make a huge difference to your productivity!