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Traditionally it has been difficult to quantify the worm burden carried by a given milking herd. This has made it more difficult to determine the cost-benefit of drenching mixed-age cows. 

We commonly assess faecal samples for egg counts in weaners and yearlings to diagnose worm burdens and assess drenching efficacy. In adult cattle however, faecal egg counts cannot be used to determine worm burdens because egg production by resident worms is suppressed by the adult cows' immune system. As well as this, faecal egg counts give no indication about the presence of encysted larvae in the gut wall (Figure 1).  

Figure 1 - Ostertagia larvae in stomach lining  From cal.vet.upenn.edu

Assessment of Ostertagia challenge to date has relied on blood sampling individual animals for pepsinogen levels. Despite this, it has been difficult if not impossible to quantify worm challenge at the herd-level. 

Nevertheless, studies have shown that worms in adult cattle do reduce appetite and time spent grazing, decrease milk production (by up to 0.03kg MS/cow/day), increase heifers' time to conception and reduce feed conversion efficiency. In heifers, worms can cause severe morbidity and even death (Type II Ostertagiasis). 

A new method for diagnosing worm challenge in milking herds is now available. This is called the BSure Milk Test. The test detects antibodies in the cows' milk.

There are a number of advantages that this test offers:

1)      Cow antibody levels are closely related to the herd's worm challenge

2)      The test can detect the level of parasitism regardless of whether cows are clinically affected or not

3)      The test detects antibodies to all the major worm species: Cooperia, Trichstrongylus and Ostertagia (Teladorsagia)

4)      The ‘production cost' of  worms in your herd can be estimated from the antibody result, allowing a cost-benefit of drenching to be made (Figure 2)

  Figure 2: Production cost of worm exposure 

5)      The test is done on the bulk tank (vat) milk and can be requested by your vet, through your dairy company (Fonterra or OCC),

6)      An accurate longer term picture of your herd's worm challenge can be gathered, as well as drench efficacy monitored

7)      Liver fluke exposure can be concurrently assessed (optional)

8)      Testing is available in spring and autumn

9)      The whole herd can be assessed for $80 (inc GST) 

In worm-challenged herds, the benefits of drenching are clear. New Zealand trials have shown strategic drenching of herds to increase production by 7.5kgMS/cow over an entire season and treated heifers conceive 12.9 days sooner than untreated controls.

Overseas trials have shown that on 30-50 % of farms, worm infection levels were high enough to cause milk-yield losses. 

Take the guess-work out of worm control. Talk to your  Vet Centre vet about the BSure test for your herd.