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Gastrointestinal disease is the top cause of mortality in neonatal calves
Rearing calves is one of the most important jobs on the farm. It takes great care and attention to detail to make sure their needs are fully met. Detecting ill health early can make all the difference to their performance both as a calf and an adult cow, therefore excellent stockmanship, nutrition, husbandry and hygiene is essential.
Because calves are born void of immunity, they are totally reliant on getting good quality and enough colostrum as soon as possible post birth. Maternally derived immunity from colostrum will help protect the calf for the first few weeks of life until their own active immunity builds up to adequate levels.
Gastrointestinal infections more commonly known as scour/diarrhoea made up almost one third of postmortem diagnoses in neonatal calves (All-Island disease surveillance report, 2022 – see Chart 1).
Chart 1 : Conditions most frequently diagnosed on postmortem examinations of bovine neonatal calves in 2022 (n=533)

As a calf rearer, this may come as no surprise as calf scour wreaks havoc across many herds and is very contagious once it takes hold. This scour is a result of any number of factors including stress, dietary changes or infectious diseases. This highlights the sensitivity of the gut in the calf.
The baby calf is born with a functional yet immature gut. The gut is one of the main immune organs and it takes time to develop post birth. It undergoes structural and functional changes and can be shortened and smoothened by getting the right ingredients into the calf.

These ingredients are mainly bioactive non-nutritive components of transition milk. They support the rapid morphological changes occurring in the first weeks of life, the period during which the intestines change most rapidly. By feeding transition milk the development of surface area can be significantly increased, as reported in a study published by Yang et al. (2015).
Cells are rapidly developing and regenerating meaning that one feed of transition milk is not sufficient, the feed received today will be shed again tomorrow as new cells generate, hence the importance of feeding transition milk with beneficial ingredients for at least the first week of life and ideally longer.
Most common infectious agents
So, once the first sign of scour appears in your calves the best thing to do is get it tested and see exactly what you are dealing with. It is impossible to know just by looking at it. Snap tests are available on the market which can give you an answer in just 10 minutes.

The All-island disease surveillance report found Rotavirus and Cryptosporidia to be the two main enteropathogenic agents associated with neonatal calf scour – see chart 2.
Chart 2: Relative frequency of enteropathogenic agents identified in calf faecal samples tested in 2022 – Percentage of positive results

Rotavirus
As the name suggests, rotavirus is a viral type of scour and usually occurs in calves aged 2-3 weeks but can occur in older calves also. It is no coincidence that the calf’s gut is also working hard at this time to reach full maturity, leaving these baby calves more susceptible to pathogens entering. Unfortunately, it is a very contagious infection and will spread to other calves. Calves will get infected via the faecal-oral route and the infectious dose is low. Dehydration can be the main reason for mortality in calves with scour, therefore rehydration therapy is essential to replace lost fluids.
So how can we help prevent it:
• Feed 10% of bodyweight in 1st milking colostrum within 2 hrs of birth & follow up with 2nd feed colostrum
• Test colostrum quality – must be >22% brix on refractometer
• Extend transition milk feeding to 14 days
• Vaccinate dry cows to boost specific antibodies in colostrum against rotavirus
• Ensure calf is removed from calving pen ASAP
• Hygiene must be tip top – calf house and feeding equipment
• Calf rearer must be clean and footdip must be available before entering calf house.
Cryptosporidia
Crypto is the second most common infectious agent to infect neonatal calves. This is a protozoan parasite and again is spread through the faecal oral route. Large numbers of oocysts are excreted by infected calves and it takes very little to infect a calf therefore very infectious in the calf house.
Calves are most susceptible to infection at around 10 days of age or can be earlier. Destruction of the small intestine results in malabsorption, fluid loss and dehydration. So once again rehydration therapy is a must.
So how can we help prevent it:
• Feed 10% of bodyweight in 1st milking colostrum within 2 hrs of birth & follow up with 2nd feed colostrum
• Test colostrum quality – must be >22% brix on refractometer
• Extend transition milk feeding to 14 days
• Ensure calf is removed from calving pen ASAP
• Hygiene must be tip top – calf house and feeding equipment
• Calf rearer must be clean and footdip must be available before entering calf house.
• Avoid housing newborn calves in the same house as calves infected with crypto – find a clean separate area
• Use a specific disinfectant which will kill crypto as the general broad spectrum will not kill it.
What disinfectant should I use in calf pens
HI Michael, This is a handy calculator to show disinfectants and amounts needed in line with DEFRA https://progiene-dairy.com/disinfectant-calculator/