Tackling Calf Scour Before Calving

Calves are effectively born with no immunity so rely entirely on colostrum to protect them against disease. Colostrogenesis (production of colostrum) starts around 3 weeks before calving; in order to get high levels of specific immunoglobulins (IgG) in the colostrum, a single dose of vaccine should be given at least 4 weeks (but no more than 12 weeks) before calving.

There have been some robust studies carried out looking at the effect of a single dose of Bovigen Scour pre-calving and then challenging the calves with Rotavirus, Coronavirus and E Coli; the results were as follows:

• No deaths in calves from vaccinated cows compared to 40% mortality in calves from unvaccinated cows.
• Decreased duration of scour and severity of clinical signs in calves from vaccinated cows.
• Reduced excretion of the bugs by ~50% in calves from vaccinated cows which means less environmental contamination.

It is important to note that colostrum management is still key in the control of calf scour; especially because the specific immunity from vaccinating the cows will only be passed on if the calf receives appropriate quantities of colostrum (10% of body weight) within 6 hours of birth. It is also beneficial to continue feeding colostrum from vaccinated cows for the first 7 days of life.

Crypto Overview

38% of calf scour cases in the UK are due to Crypto (Cryptosporidium Parvum); the second most common cause is Rotavirus. Interestingly, Crypto is also the second biggest cause of child diarrhoea and death worldwide which makes it a true ‘one health’ topic.

Crypto is very complex in terms of immunology which makes the development of a vaccine almost impossible. It also only requires a few oocytes to cause disease in a calf, but each calf will excrete 1010 oocytes in a 1-2 week period following infection. This makes managing the level of environmental contamination very difficult. Steam cleaning is essential followed by an appropriate oocidal disinfected (such as Interkokask).

Successful treatment protocols for Crypto need to reduce the severity of the clinical signs, limit the number of oocytes excreted and avoid re-infection whilst allowing the calf’s own immunity to develop. There are two options:

• Halofuginone is Crypto-static which means it slows down the rate of infection but doesn’t kill it off altogether. Halofuginone has a very narrow safety index (it is toxic to calves at 2x the normal dose and lethal at 10x the dose) so accurate dosing for the calf’s weight is essential. Halofuginone is best used as a preventative by dosing calves from day 1 for 7 days. It is also advisable to give it on a full stomach (i.e. during or <1hour after a milk feed) and not to used in calves that have already been scouring for >24 hours.
• Paromomycin sulphate is a relatively new product for treatment and prevention of Crypto and available as both an oral drench (fed for 7 days) or powder for adding to milk replacer. There are fewer safety concerns compared to Halofuginone.