Now that it’s rained…we may get more than we bargained for
Rain was badly needed and now that it has arrived, we can look forward to a burst of grass growth. But farmers need to be aware that it is highly likely there will also be a sudden emergence of infective lungworm larvae that could cause outbreaks of hoose.
Worm control in cattle has been challenging this summer due to the exceptionally dry weather and the emergence of ivermectin resistance.
It is inevitable that grazing cattle are exposed to parasitic worms and with intensification, increased herd sizes and tighter grazing practices, the burden and impact of these worms is increasing.
For many years farmers like Denis Leamy, a former Munster and Ireland rugby player, have changed to Dectomax to help manage and control the impact of these worms on performance.
Work carried out last year by Teagasc showed that 16 of the 16 farms tested had resistance to ivermectin injection.
The calves were not showing signs of scouring; but when worm egg counts were carried out, resistance was found and the products were not fully effective.
Significantly, when the performance of the calves was compared to those of animals treated with an effective product, it was found that they weighed on average 7kg less after a month. This would equate to a loss of 140kg over a group of 20 calves, or it would be like losing a calf every month and not noticing that it had gone.
Where there have been reported issues with ivermectins and white doses, Dectomax is different and there have been no reported cases of dosing failure.
Another advantage of using Dectomax is that it has at least a five-week period of persistent action against stomach worms and lungworm, giving a dosing interval of eight weeks.
This is why Denis Leamy has been using Dectomax to good effect for the last few years. He had concerns regarding ivermectin resistance, which is now a reality on Irish farms and is causing a drop in performance.
He realised that not all products have a persistent effect against the worms, so the inter-dosing intervals will vary. But, with Dectomax, he could use it every eight weeks, resulting in less labour and superior protection.
The dry weather we have experienced this year has meant that lungworm larvae have not been able to spread onto the pasture nor survive as long.
However, now that the rain has finally arrived, large numbers of larvae that have been trapped inside crusted dung pats will suddenly emerge onto the pasture; potentially causing serious outbreaks of hoose.
The diagram below illustrates a few different scenarios that may have occurred this summer. Due to the late turn out and poor conditions early in the summer, many calf dosing programmes did not start until the middle or end of June.
The white doses (benzimidazoles) and yellow doses (levamisoles) have no persistent effect and only kill the worms at the time they are used. The ivermectins will persistently kill worms for two-to-three weeks. Dectomax Pour On and Injection persistently kill worms for at least five weeks.
There has been little or no rain since June, but now the rain has arrived. The red curve illustrates the degree of challenge from lungworm larvae.
Calves/weanlings will be picking up lungworm larvae in the middle of August and if they had been dosed with a white or yellow dose or an ivermectin as shown, they could be coughing and suffering a loss in performance.
However, the Dectomax programme will still be protecting the calves and will kill off these infective lungworm larvae before they can cause any damage.