“The cryptosporidiosis outbreak was a nightmare. It involved shocking work over two to three weeks, keeping calves alive through feeding electrolytes and water – not to mention the cost of treatment and the loss of a few calves.”

This is how Westmeath dairy farmer Michael Clarke summed up his experience of cryptosporidiosis in his 250-cow herd.

Michael and his wife Lynn farm at Clontytallon, Gaybrook, a couple of miles from Rochfortbridge. They have four children – Sarah (15), Liam (13), Grace (11) and Stephen (8).

Cryptosporidiosis is one of the main causes of scour in calves less than two weeks of age. Caused by the parasite Cryptosporidium parvum, it results in acute scour and abdominal pain.


“We had the first outbreak in 2017. It didn’t hit until around 7 March when most of the cows had calved.

“In 2018, it came much earlier – around 22 February. And last year, it came even earlier, right in the middle of calving,” said Michael.

He described the “shocking work” involved in keeping calves alive with electrolytes and water and calves not drinking properly. At one stage, their vet John Moore had to put eight calves on a drip. Four of them died. “The labour and the cost was horrendous,” said Michael.

It was after this episode that Michael decided, following the advice of John, that to get on top of cryptosporidiosis, all calves must receive the oral solution from birth.

Oral solution

As soon as cryptosporidiosis was diagnosed in 2017, John Moore prescribed the oral solution which is licensed for the treatment and prevention of diarrhoea caused by Cryptosporidium parvum. Containing the active ingredient halofuginone, it is available only on veterinary prescription.

  • As a treatment, it should be given to calves within 24 hours after the onset of diarrhoea, once a day for seven consecutive days. Make sure calves are fully hydrated before treating them with the oral solution.
  • As a prevention, it should be given to every calf 24 to 48 hours after birth, once a day for seven consecutive days.
  • Michael Clarke administered the oral solution in 2017, 2018 and 2019, only after the first calves were diagnosed with cryptosporidiosis in each of these years.

    “Last year, when the disease hit earlier in the calving season, we treated all newborn calves with the oral solution. As a result, the problem reduced dramatically. We will give it to all calves from one day old this year.”


    The Clarkes are very diligent in their calf-rearing practices. Calves are given plenty of colostrum within a few hours of birth and close attention is paid to nutrition levels and to bedding, hygiene and ventilation. This demonstrates that even with good management, cryptosporidiosis is an ever–present risk.

    Up to this year, calves were reared in the same air space as the in-calf cows. A new stand-alone calf shed has been erected in which all replacement heifer calves will be reared.

    Lynn will take full responsibility for the calf-rearing operation and will ensure that the strictest bio-security measures are adhered to.

    Disease can get out of control

    Veterinary practitioner John Moore (pictured below) said where cryptosporidiosis is a problem on a farm, the use of the oral solution should be a critical component of the prevention programme.

    “All calves should be treated daily from 24 to 48 hours old for seven consecutive days.

    “Because the disease hits so fast, it can get out of control before the farmer has time to take action. Mortality can be high and even when calves survive, thrive can be severely affected.

    “While the oral solution is not cheap, its use as a prevention is a more economical option than the massive labour, stress and cost involved in treating sick calves, as well as the potential losses from dead calves and poor thrive in those that survive,” he stressed.

    He highlighted the importance of strictly following the instructions on the use of the oral solution.

    “Dosage levels should correspond to the weight of the calf and when used as a treatment, make sure the calf is fully hydrated and bright before use.”

    Vet John Moore.

    Period of rapid expansion

    The Clarkes converted to dairying in 2010. They ran a suckler herd of 100 cows and bought in around 140 weanling bulls. There was also a flock of 100 ewes.

    They bought 200,000l of quota under the new entrant scheme and started off milking 48 heifers.

    Last year, they milked 250 cows. This year, they will calve 273 and plan to milk around 260. The remainder are being sold as in-calf heifers.

    “Our plan was to milk 120 cows. But a neighbouring farm of 114 acres came up for lease and we decided to go for it. An additional 50 acres also became available and we leased that too,” said Michael.


    The herd is 50/50 Holstein Friesian and Friesian/Jersey crossbreds. All cows are bred to AI bulls. Around 15% are bred to Angus and Hereford. Bull calves are sold at two to three weeks and most of the heifer calves are reared for replacements. The milk is supplied to Lakeland.

    Lynn had an off-farm job in Athlone, but decided to give it up after their third child was born. That, and the low returns from beef and sheep, put pressure on the family finances. They decided to take the plunge and convert to dairying.

    Lynn, who was born and reared on the south side of Dublin city, has made the perfect transition to farming life and is now a vital and energetic partner in the business.

    They employ one full-time labour unit, Conor Hanlon from Offaly, who spent a number of years working on a dairy farm in New Zealand.

    Millions of oocysts

    As part of its life cycle, Cryptosporidium parvum produces huge numbers of encysted eggs, or oocysts, which are shed in the faeces of infected calves, cows or other animals.

    At peak shedding, there may be as many as 10 million oocysts per gram of faeces. It takes as few as 10 of these to cause disease in young, susceptible calves.

    Typically, clinical signs appear in calves from five to 14 days old. These can vary greatly – from mild diarrhoea to severe, watery scours and eventually death. Calves become rapidly dehydrated and suffer loss of appetite.