Importance of colostrum

New Zealand studies have shown 25% of one day old calves have had no colostrum and up to 40% have not consumed enough colostrum. It is critical that a calf gets high quality colostrum within the first 24 hours and, preferably, within the first 12 hours.

Calves with inadequate immunity from colostrum are four times more likely to die and those that survive have lower weight gains, poorer feed conversion efficiency and a higher incidence of scouring than calves with good levels of immunity gained by drinking good quality colostrum in their first 24 hours.

Development of immunity

Calves are born with a very immature immune system and immunity is obtained from the cow through immunoglobulins in her colostrum. These immunoglobulins are large protein molecules which can only be absorbed move through the calf’s intestinal wall for the first 24 hours after birth.

By this point the wall of the small intestine has matured to the point that these large immunoglobulins can no longer pass through. In addition, the secretion of digestive enzymes starts 12 hours after birth, these enzymes digest and break down immunoglobulins rendering them useless.

The young calf is born with no resistance to diseases like E. coli and salmonella, so its only protection in these first few days is from colostrum (this is called passive immunity). A calf with no immunity can get sick when challenged with just 500 salmonella bacteria, whereas one that has received a good level of passive immunity can withstand 10 billion Salmonella bacteria.

By the end of the first week the calf is starting to build its own immune system and produce its own antibodies in response to pathogen challenges. Within a few weeks the calf is well on its way to being able to fight off disease.

Development of passive and active immunity in the calf

Why do calves miss out on colostrum from their mothers?

While many calves do get colostrum from their mothers but a lot don’t. The practice of removing calves from dairy cows for generations has undoubtedly reduced the cows mothering instinct.

Some dairy cows are apt to wander off soon after calving. Calves can go under hot wires and selection for milk production means that some udders are low and difficult for calves to access.

Six hours after birth, around 25-30% of dairy calves will not have suckled and 20%will not have not suckled within 18 hours. Daily calf collection (if not twice daily collection) is the right thing to do – however, do not assume that the calf has had enough colostrum from its mother before you pick them up. New arrivals to the calf shed need to be fed colostrum unless you are sure they have had colostrum from their mother. Waiting until the next day when they will be “hungry” is too late. If necessary, the calf should be tube fed although this reduces the efficiency of absorption of the antibodies.

The amount of protection a calf obtains from colostrum is determined by the amount of antibodies ingested and the amount that is absorbed. The amount ingested is affected by the volume of colostrum consumed and the concentration of the antibodies in the colostrum. The calf should get 5-6% of its bodyweight as colostrum in the first six hours and the same amount 12 hours after birth to ensure that at least 100g of antibodies are consumed. This equates to about 2 litres of colostrum per feed for a 40 kg calf.

Factors affecting the quality of colostrum  

Antibody levels are highest in the first milk produced after calving and then drop rapidly so colostrum fed to calves in the first 24 hours should be first milking colostrum only see figure below). Antibody concentration varies between cows with a Dairy NZ study showing an average of 48 g/l but with a range from 20 to 100 g/litre (see figure below). Ideally, a calf should be fed first milking colostrum from a mixed age range of cows—to give the calf a wider range of antibodies. Cows which have been vaccinated (e.g. against rotavirus) will produce more antibodies to the pathogen they have been vaccinated against. Cow breed, age, her exposure to pathogens and nutrition all affect the quality and volume of antibodies.

Feeding energy-deficient diets prior to calving reduces both production and quality of colostrum. Generally, dairy breeds produce more total immunoglobulins than beef breeds and older cows produce more immunoglobulins than heifers as they have been exposed to more diseases.

In another study, we bled calves on arrival from 9 dairy farms to look at colostrum status. GGT less than 50 indicated no colostrum and GGT levels between 50 and 200 indicated marginal colostrum. Around 22% of calves had nil to marginal colostrum. Death rates were higher in the no colostrum group (13%) and the “inadequate colostrum group (11.1%) than in the “good” colostrum groups (4%).

Colostrum status of calves sourced from 9 dairy farms

There was variation between source farms in apparent colostrum intake, with a range in mean GGT (colostrum) levels of 360 up to 942 U/l. Calf mortality ranged from 1.2% up to 12%. The farms with the lowest colostrum intake had the most calves in the sick pen and the highest mortality.

Farm effects on colostrum level, deaths and sickness.

When we looked at colostrum level by arrival batch, it was clear colostrum level was declined as the season progressed. Calf rearers often experience having more sick calves as the season progresses. This has generally been put down to a build-up of bugs through the season as the shed gets dirtier and the weather warms. Yet here is evidence that declines in calf colostrum status may increase the risk of calves getting sick. Presumably, this is due to a decline in standards on the dairy farm as the season progresses.

The effect of arrival date on colostrum level across all farms.

Sick calves

Most problems occur in very young calves and by the time calves are 2-3 weeks old and eating pellets the incidence of problems drops dramatically. An early indicator of a problem is often scouring. There are three possible causes – stress, nutritional (both management issues) and infectious agents. There may be more than one causative agent and identification of the actual cause is often difficult. The number and timing of calves scouring is often a clue as to the cause.

• More than 40% calves scouring: Often an indication of a problem with the milk. May not be curding, the concentration may have been mixed wrongly or too much is being fed.
• Between 5% and 40% calves scouring: Often an indication of cryptosporidia infection. This is a caused by a protozoa which is widespread in calf sheds. It particularly affects young calves up to 10 days of age. The infection builds up over a few days and can affect a significant proportion of calves in the shed. The treatment is to remove from milk and feed electrolytes for a day.
• Less than 5% calves scouring: A few scouring individuals is often the sign of something more sinister – particularly if they go down very quickly. Consult your veterinarian. Potential culprits are rotavirus and salmonella. Isolate and treat with electrolytes. Salmonella is caused by a bacterium and can be treated with antibiotics. If a recurring problem on the property then young calves can be vaccinated. Often rotavirus and salmonella are secondary to a cryptosporidia infection which makes treatment more difficult.

Stress scours. Can be caused by difficult birth, bad or sudden change in weather, transport, environment (e.g. over-crowding, cold, damp, draughty or humid conditions inside calf sheds). Even changes in staff and hygiene can increase the likelihood of scours. The stress of transporting calves from the sale yards or from one farm to another may be sufficient to cause scours if calves are offered milk on arrival. Newly arrived calves should be fed an electrolyte.

Nutritional scours. Often caused by overfeeding or by a rapid change from colostrum/milk regime to a milk powder regime. The initial digestion of milk occurs in the abomasum (or fourth stomach) and then in the intestines. Nutritional scours is due to inadequate milk digestion in the abomasum. This means the milk leaves the abomasum too early and overloads the intestine with lactose. This results in a watery scour and the fluid loss results in a very dehydrated calf.

Infectious scours. Caused by a range of pathogens including cryptosporidia, coccidia, salmonella, E coli and rotavirus.  But generally, the better the immunity obtained from colostrum, the better the calf copes with disease challenges. In a calf that has had inadequate colostrum as few as 500 salmonella bacteria can result in a sick calf while a similar calf with an adequate colostrum intake can cope with as many as 10 billion bacteria before it gets sick to the same degree.

 Rotavirus From our calf rearer surveys, we know that rotavirus is the biggest animal health issue facing calf rearers with some reporting death rates as high as 30%. We also battled with rotavirus twice and it doubled our calf mortality – from less than 3% to 6.7% and 5.4% in the two years when we had rotavirus outbreaks.

Rotavirus is devastating and demoralising – for both calves and rearers. Since it is a virus, antibiotics are ineffective. Treatment with large volumes of electrolytes is labour intensive and time consuming, and not always effective. Even if the animals do recover, they will still shed large numbers of virus particles into the environment, potentially infecting healthy calves. Recovered calves grow slower and are more susceptible to other diseases, and calves can become re-infected. It is persistent in the environment, and can remain infectious for many months at room temperature. It can withstand low temperatures and high humidity on non-porous surfaces like plastic and concrete.

What is it and how does it kill calves? Rotavirus infects and destroys mature cells on the tip of the ‘villi’. Villi are the tiny, finger like projections on the surface of the small intestine that help absorb nutrients from the digestive tract. Damage to these cells not only reduces absorption of nutrients from milk and electrolytes, but results in fluid loss from the intestine, further compounding the level of dehydration. It is this dehydration which kills calves. Rotavirus increases the concentration of calcium in the intestinal cells which acts like a toxin and results in the pale yellow scour associated with Rotavirus.  

How is it spread and what are the signs? Rotavirus affects calves up to 3 weeks of age and is spread primarily by calves ingesting faecal matter containing virus particles, but it can also be inhaled, particularly the shed is highly contaminated. Infected animals shed large quantities of the virus into the surrounding environment, contaminating the shed area and increasing the risk of other animals being infected. The rate of spread depends on the level of environmental challenge the calf is exposed to but typically between 24 – 48 hours after infection. The most obvious sign of Rotavirus in calves is a pale yellow scour, often rancid smelling, this leads to rapid fluid and electrolyte loss and, therefore,  dehydration. Rotavirus initially needs to be confirmed with a lab diagnosis but rearers who have already experienced are likely to identify the presence of rotavirus very quickly. The key is to identify infected calves very fast, isolate at the start and treat promptly with electrolytes. Make sure you have good hygiene to reduce the rate of spread. At every feed it is important to cast an eye over each calf to identify any potential signs of illness. These may include

• Hanging back from the feeder/reluctance to come in and feed
• Reluctant to drink, fussing with teat, coming off teat
• Wet tail, pale yellow scour – can sometimes be watery/and bloody

Most calves that die of rotavirus, die from loss of water and electrolytes, rather than the direct action of rotavirus. Rapid treatment with electrolytes is critical. Scouring continues until the villi inside the small intestine are again covered with mature cells that allow the resumption of normal digestive-absorptive processes. Don’t stop feeding milk but don’t mix electrolytes and milk at a single feed. It is important to keep the calf’s energy levels up, as well as continuing to provide the calf with antibodies with which to fight the virus. Many electrolytes contain sodium bicarbonate that alter the pH in the digestive tract and adversely affect milk absorption, so milk and electrolytes should be fed at least two hours apart. Animals may continue to shed the virus in their faeces while not showing clinical signs. Calves do not become “immune to rotavirus” and they can get re-infected. However, the second infection is usually a lot less severe.

 Treatment of scouring Feeding of electrolytes to scouring calves is labour intensive but it is critical to maintain fluid levels. Calves which are scouring and dehydrated need to have the lost fluid from scouring replaced as well as their normal fluid intake. If a 40kg calf has lost 10% of fluid it will need 4 litres just to replace the water it has lost.  While the recommendation to stop milk feeding for 24 to 48 hours remains true for nutritional scours, the recommendations for infectious scours has changed in recent years. Now the belief is that it is important to keep feeding at least some milk to calves especially if they will still drink. Electrolytes provide energy but no protein and removing milk for any length of time reduces the ability of the calf to fight infection. If milk is with-held for longer than 2 days the epithelial cells in the gut become dysfunctional and when milk is introduced, the milk itself can cause scouring as it cannot be digested. Scouring calves can lose up to 5 litres of fluid each day including minerals salts essential for normal body function which is why it is usually the dehydration and acidosis that kills the calf.

Current recommendations are to feed milk and electrolytes separately – with at least two hours between the two.  If the electrolytes and milk are mixed or fed too close together the milk will not curd and this will increase the level of scouring.  Therefore, the electrolytes needed to be administered as extra feeds.  This also means that the calf is getting fluids on a more regular basis maximising the potential absorption of the poorly functioning gut.  While electrolytes can be tube fed, it is much better if the calf will drink the milk so that the milk bypasses the rumen via the oesophageal groove.

How do we prevent it?  There is no silver bullet although vaccinating cows against rotavirus and then feeding calves with colostrum and milk from these calves in the first 24 hours helps. This provides the calf with some passive immunity against rotavirus Unfortunately, the passive immunity declines in the days after birth and there is a risk period before the calves own immune system is functioning properly and often the peak incidence of Rotavirus infection during this period between 5 and 14 days of age. Nevertheless, the more rotavirus antibodies a calf gets from colostrum and the older it is before it is challenged by rotavirus, the more likely it is to survive.  Antibodies in colostrum/milk can continue to provide limited local immunity in the gut (even though they can’t be absorbed through the calf’s gut) so feeding milk from vaccinated cows will also help prevent the development of rotavirus.                  

 Hygiene reduces the environmental contamination. Your shed needs to be thoroughly cleaned out at the end of each season and sprayed with a virucide solution. Since the whole idea is to keep the amount of virus contamination to a minimum, spray your shed every 3-4 days with a virucide solution throughout the risk period (i.e. until the youngest calves are two weeks of age). Many solutions are suitable for spraying over calves.

Maintain a high standard of cleanliness in the shed and thoroughly clean and disinfect equipment such as feeders, especially equipment used in the sick pen. A bucket of virucide can be kept handy to soak bottles and teats in when not in use. Minimise equipment (including gumboots) and movement between pens with sick animals and uninfected pens especially at the start of an outbreak- once the outbreak is in full flight the shed is contaminated so less important. Initially, try to isolate sick calves away from health calves to avoid contamination- this also helps with managing the extra feeds of electrolytes. Keep a close eye on who is coming into the calf sheds and try to avoid contamination from other farms (apart from people feeding the calves minimise the number of visitors to your shed in the middle of a rotavirus outbreak).  If calves are coming from a number of sources, pen calves from the same farms together and group calves according to age.

Our experience.  Own experience with rotavirus started on the 13^th August when we had 435 calves in the shed. They ranged in age from new arrivals up to calves which had been in the shed for 21 days. Within 3 days of the first case of rotavirus being diagnosed, it had spread through the shed, with some calves in each pen affected. Younger calves were hit the hardest but even the oldest calves were affected. However, the older the calf the greater its chance of surviving and we had no deaths in the calves over two weeks of age. In total, 46% of the calves we reared were affected and at the peak it was all hands to the pumps and we were treating over 80 calves. The shed was obviously so contaminated that it was not practical or worthwhile to isolate calves so we stopped trying and concentrated on dealing with the problem. Most calves were on a once-a-day milk feeding system and we continued to feed milk in the mornings. Any calf that we had any reservations about got a blue neck band so that we knew to monitor it. Any calf that had a wet tail got a pink band and was fed electrolytes in the evening. Where the majority of the pen had pink bands, it was just as easy to feed electrolytes to all the calves in those pens as chances are the other calves were going to need it soon anyway. Any calf that was wobbly, wouldn’t feed or down got a red band and was taken to the sick pen. In total, 8% of calves were taken to the sick pen and 44% of the sick pen calves subsequently died. Overall, shed mortality was 5.4%. Calves in the sick pen were fed milk in the mornings and electrolytes at midday and evening (either by tube or bottle). As a general rule, calves in the sick pen need as much electrolytes as you have time to get into them. Within 10 days, we had worked our way through the worst of the outbreak but any new calves which were brought into the shed went down within 48 hours in spite of regular spraying of the shed. We felt that we had a very level of contamination within the shed which was even swamping the good healthy colostrum fed calves. The only solution was to put new calves into a completely different shed. It is worth noting that we also had 3 outbreaks of salmonella in the shed. Yet this was quickly recognised as being different, the affected pens were treated with antibiotics and no calf died from salmonella.

 Because we had rotavirus problems the previous year, we had sourced our calves from supposedly vaccinated herds. This probably made us over-confident. The pens were clean, calves were happy and we weren’t as diligent as we should have been with the early virucide spraying of the shed. This probably led to the build-up of contamination to the level where it became a major problem.

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