The first month of Life
1. Scale of the problem
Calf scours is the major cause of loss nationwide of cattle under 12 months of age. Losses in the range of 8-12 % can occur in dairy farms and 2-6% in beef farms.
Incidence of disease can be up to 100% in some dairies, and 30% in beef farms. It is a disease that is poorly understood given the immense cost to industry and the welfare problems it creates.
In calves under 1 month of age, one, or a number of infectious agents almost always causes scouring. The most significant ones are
In all cases, spread is by ingestion of infective organisms which are shed in their millions in every gram of faeces.
E.coli is a bacterial infection, which is only really seen in the first 4-6 days of life. The bacteria adhere to the gut wall and produce a toxin that causes water to be secreted into the gut. Hence E.coli infection causes rapid dehydration, with profuse watery diarrhoea without blood.
Salmonella by contrast, occurs at any age, but current thinking is that affected calves are initially infected within the first few weeks of life. The bacteria tend to invade deeply into the body organs and causes severe systemic disease, often with pneumonia. Affected calves often have bloody, frothy diarrhoea with mucus and a fever. The degree of disease is thought to be dependant on the initial infective dose, with calves ingesting large doses destined to die.
Rotavirus and Coronavirus cause disease between 10-14 days up to about 20 days. The virus invades the lining of the gut and causes the lining cells to shrink, reducing the body's ability to absorb nutrient. Because they are viral, there is no specific treatment. They are highly contagious
Cryptosporidia is a parasite commonly associated with damp conditions. The eggs can survive years in the right environment. In lab conditions, it only causes minor diarrhoea, and some researches question whether it as the potential to cause death. Recent outbreaks though have confirmed that by causing damage to the gut, secondary effects from bacterial overgrowth can cause significant losses. It is mainly seen from 18 –28 days, and can have a relapsing course.
3. What Happens to a calf with Scours
Irrespective of the cause of the disease, there are some changes that are consistent, and need o be understood, if they are to be treated effectively.
(a) Dehydration from fluid loss.
(b) Acidosis from bicarbonate loss
(c) Sepsis from either primary or secondary bacterial invasion
(d) Hypothermia from reduced ability to maintain body temperature
(e) Low blood sugar from reduced feed intake
(f) Low blood protein from faecal loss and starvation
a) Dehydration is first on the list for a reason. By the time a calf looks dull and sunken in the eyes, is often severely dehydrated. Estimates can be made from the time the skin takes to return to normal after being tented up, or by the number of millimetres of eyeball recession. I don't think it really matters. I usually work on all calves being 10% dehydrated, and balance it up after that.
b) Acidosis has been historically overlooked in treatment of sick calves, because it is difficult to measure in the field. Its role though is becoming increasing recognise as a major change in calves, more so than in other species.
c) Bacterial involvement has always been the major concern of farmers in treating scouring calves. Whilst necessary in some cases, in the majority it more rightly regarded as covering in the case of secondary infection. If the concern is the calf becoming septic, then it makes sense to use treatments that will provide god systemic cover.
d) Hypothermia is a major problem in sick calves. As they deteriorate, they lose the ability to maintain their core body temperature. Once it gets below 35deg, the chances of survival are dramatically reduced.
e) Low glucose will occur in calves that have been fasted, or have failed to suck for more than 24 hours. By 48 hours the calf can start to become dull and depressed because its blood sugar is so low.
f) Calves who have been sick for an extended period (4-5 days), or calves that are losing a lot of protein in the faeces with Salmonella, can rapidly loses enough protein to keep the fluid inside the blood vessels.
Rational treatment relies on understanding what is happening, and likely to happen to the calf. It also depends on the age of the calf, and how severely affected the calf is. I think the most rational approach is to stage treatments according to how the calf is looking, and the herd history. Obviously if a farm has a historical problem with Salmonella, and you are in the midst of an outbreak and have suffered losses, treatment will be different to a one off case.
i) Calf is scouring, but is bright and happy, feeding well and apparently unaffected. These calves in the majority of cases do not need treatment, unless the calf is less than 4 days of age, or has other considerations. There is probably more risk of spreading disease by bringing in a mob of cows and calves to the yard, than benefit in treating.
j) Calf is scouring, and obviously dull, but up and drinking. Oral fluids with alkalising agents are indicated. I will normally leave them on the cow, but make sure they are in a sheltered area where they can be brought in easily for treatment. The calf needs to be removed from the mob to reduce the risk to other calves. It is worth covering them with injectable antibiotics to prevent secondary infection.
k) Calf is dull and dehydrated, and not drinking. This calf will need intensive treatment. I prefer to initially treat with intravenous fluids and then oral electrolytes. On farm fluids given under he skin are highly effective as well. If it has not drunk after 24 hrs, I will tube feed it with milk. Isolate the calf and if possible put it in a dry shed. IV antibiotics.
l) Calf is flat out and cannot stand without help. Bring it into the surgery for treatment. Even with these calves, we have a 70% success rate; those that die are generally Salmonella cases with secondary organ disease.
Types of Fluid Treatment
None of the commercially available fluids are ideal! My current preference is for Megalyte Plus as it contains adequate alkalising agents. The main thing is to give adequate volume. A 40kg calf that is 10% dehydrated needs to drink 4 litres to make up the deficit + 6l for daily maintenance + whatever extra volume it is likely to lose in the day. That means many of the calves need at least 10-12 litres in the first day! That is 6 2 litre feeds.
I usually use Hartman's solution, which is available in either 1 or 5 litre bags. Even 2l under the skin makes a huge difference to a very flat calf.
Traditionally we have used Hartman's solution run in through a drip line. This is still the preferred treatment but is slow and reasonably expensive. I am now using Hypertonic saline at 4-5ml/kg iv over 10 minutes followed by 2l oral fluids in calves not assessed as being severely acidotic. Acidotic calves are treated with hypertonic Sodium bicarbonate at using the following formula
Base deficit * Bodyweight * 0.5 = ml 8.4% NaHCO3
It is essential that the oral fluids be given within the 5-10 minutes after IV hypertonics.
Diagnosing systemic infection can be quite difficult in calves, and body temperature is not necessarily much of a guide. My belief now is that there are some consistent situations where antibiotics are indicated.
1. Calves with scours within the first week of life. This is likely to be E. coli or Salmonella.
2. Calves that are actually showing signs of being dull and depressed. Secondary bacterial invasion does occur, and antibiotics have been shown to reduce the death rate.
I firmly believe that in both these cases, injectable antibiotics are preferable to oral medications on the following grounds.
a. If you are concerned about systemic disease, then it makes sense to use systemic antibiotics that will have higher tissue levels
b. We can achieve more predictable blood levels by using injectable drugs
c. Much wider range of medications available
d. Less disruption to developing gut flora.
After 20 years in practice, I am yet to see a published paper recommending oral administration in cases of calf scours
Calves are very prone to becoming cold, especially when they become acidotic. Normal range is between 37.2- 38 deg Celsius. Often they are found with a rectal temp less than 35 deg, and it is critical to provide these calves with warmth. If the rectal temp is less than 33 degrees, survival rates are poor.
Normal calves suckle 5-6 times per day and consume ~20-25% bodyweight in milk. I.e. a 40kg 2-week-old calf will drink about 8-10l of milk per day. If they are off feed for more than a day, or suffering from chronic malnutrition as many dairy calves do (old Dept Ag. recommendations were to feed caves 10% of bodyweight), then any interruption to feed intake can result in a very low glucose which will resent as a dull, depressed or comatose calf. Milk is the preferred treatment for this, but often they will need IV glucose initially to restore normal levels quickly.
Chronic scouring calves frequently have reduced feed intake and excessive protein loss. Coupled with often low colostral globulin levels and we will see low protein in calves that have been sick for 4-5 days or greater. Again, milk is the preferred treatment, but some calves will need a plasma transfusion if their blood protein levels drop to the point where they are no longer able to hold fluid within the blood vessels.
In theory, prevention is straightforward.
What we need is to have a calf that is born without difficulty, stands and sucks adequate colostrum quickly and stays in a clean environment free of contaminants. These are the three critical elements in minimising the disease.
1. Avoid difficult births by joining heifers especially to low birth weight/ gestation length bulls.
2. Ensure ample colostrum intake. New recommendations are for calves to be given 4l of colostrum within the first 12 hours of life. Dairy calves probably will not drink this much and will need to be tube fed. Because colostrum contains laxatives, don't be surprised if they are a bit loose after this much colostrum!
3. Hygiene. It is the most critical element of all, especially in dairy set-ups. Areas where calves have been previously are the biggest risk factor of all, so there needs to be some method of reducing the risk of exposure of young calves to older calves. In beef properties, this is best done by a combination of 3 things.
i. Calve heifers down before the main mob by 3 weeks
ii. Keep the joining period down to 9 weeks. Draft cows that have not yet calved off the calved cows every 3 weeks, so they calve on clean pasture.
iii. Make sure there is ample shade and shelter, and watering and feeding points in calving paddocks, so the calves are not forced to congregate in the one area. Mobs can be boxed together after the youngest calves are about 6 weeks of age.
Other points to note:
Avoid bringing in foster calves wherever possible.
Calves older than 3-4 weeks of age with scouring may well need worming, have coccidia or something else.