In New Zealand we’ve recently shown that cows that were anaemic with theileria had poor reproduction performance with a 25% lower three-week submission rate, 24% lower first service conception rate, 17% lower six-week in-calf rate and an 11% higher empty rate compared with unaffected animals. The cost was $40/cow or more than $20,000 for the herd.
However, not all herds in which theileria is diagnosed appear to have significant production or reproduction problems. There’s less impact if they’re infected in late lactation, with relatively few animals affected in the following lactation.
The disease has affected more than 500 farms in the upper half of the North Island and while it’s been in NZ for more than 30 years, a new virulent form (ikeda) arrived in late 2011 or 2012. Affected animals are anaemic and so are slow to move, have faster breathing, have pale or yellow vulva or udder and lowered milk production.
On most farms, only one or 2% of animals are clinically affected and generally fewer than 0.5% die but some farms have had much higher rates of both sick and dead animals. There are generally more animals infected than are clinically evident.
More than 30% of the cows were carrying the parasite, and 7% were severely anaemic, when a whole herd was recently bled. So why don’t these anaemic animals show clinical signs?
It appears that if animals are not stressed they can to some extent compensate for the anaemia. Over time immunity will develop and their red blood cell count will increase back to normal.
What do you do if you’ve got theileria on your farm?
First identify potential cases, confirm the diagnosis and manage these cows to reduce stress. One way of identifying cows is to look at the vulva of each cow at milking and see how pale or yellow and membranes are. There is a handy reference card, the FANI card, available from your vet or the Ministry for Primary Industries for this purpose.
The presence of the parasite can be confirmed with a blood test, then you can minimise their stress. If milking, reduce to once-a-day and hold them in a paddock handy to the dairy. For animals more severely affected, blood transfusions and iron injections are helpful. There are also some antimicrobial treatments that may support these animals.
How do you control theileria?
It would appear logical to try to reduce tick numbers but ticks have three phases of their life-cycle (larvae, nymph, adult), with ticks falling off the animal between feeds. So, further work is required to assess the impact of tick control.
Can we prevent theileria getting onto a farm?
First find out if it’s on your farm, then think about blood-testing animals coming on to the property. Application of a tick control product before stock arrive may reduce the probability that infected ticks are brought in but if you have ticks on your farm transmission can still occur.
There’s also a suggestion infected ticks may be travelling between farms on hares or deer. It has been shown that farms within 5km of a theileria outbreak are more likely to get theileria than farms further afield, independent of cattle movements, which goes for much of the upper half of the North Island.
While theileria is here to stay the good news is that with early identification and appropriate supportive therapy, the risk of illness and death can be managed.
