BRAHMAN NEWS JUNE 2014 ISSUE #183 PAGE 42
By Alex Ashwood
Scours in beef calves are caused by digestive disorders, viral and bacterial infections, worm infestations and parasites.
"Coccidiosis is a parasitic scour that reduces animal performance"
Coccidiosis is a serious type of parasitic scour which is most common in dairy calves but can occur in young beef stock when the animals are under stress and are contained in crowded contaminated yards or overgrazed pastures around creeks and dams.
This disease is caused by microscopic, one celled protozoa that live inside the intestine of infected stock. Clinically affected young stock are a ready source of infection, however, older stock which are usually resistant to the clinical disease can be sources of infection to young susceptible animals.
Following infection, the stock gain tolerance or immunity which provides protection even though they continue to be infected.
"The most common species of coccidia in Australia is the Eimeria spp"
Coccidiosis is a self-limiting stress induced parasitic disease associated with smelly bloody diarrhoea, poor growth and dehydration and in some cases seizures and death. Clinical signs of coccidiosis occur most frequently in young calves but in favourable conditions may occur in weaners and yearlings. Clinical stages of coccidiosis often account for 5% of infections but the non-detected subclinical cases (95%) are responsible for the greatest proportion of wastage and production loss.
"Susceptible stock are most at risk when they come in contact with infected stock"
Coccidia eggs (oocysts) are commonly found in the intestinal cells and the parasite passes into the faeces. Under favourable conditions (warm-damp environments) the oocyst develops into an infective form which leads to infection when ingested from contaminated feed, soil and water by susceptible animals.
Until digested by stock, the infected form is protected from adverse conditions (low temperatures and dry conditions) by a cyst wall for up to 2 years. Under favourable conditions the oocysts can quickly turn into the infective form (5-10 days).
The oocysts release sporozoites (larvae) that multiply asexually in the cells lining the wall of the small intestine and release thousands of microzoites (2nd generation larvae). The merozoites then enter the large intestine and go through a sexual reproduction cycle to produce thousands of oocysts which are passed out in the manure contaminating soil, feed and water.
"The highest production losses occur in the undetected subclinical stage"
It is estimated from the ingestion of 125 oocysts, producing 100,000 merozoites, can cause damage to more than 6 billion intestinal cells.
About 70% of the life cycle occurs in the small intestine where there are rarely clinical signs although calves are often depressed and losing weight. It is only when the protozoa enter the large intestine in the later part of the cycle that infestations cause diarrhoea and blood in the faeces due to damage of the lining of the gut.
Destruction of the intestinal cells and damage to the cecum and colon interferes with digestion and the absorption of nutrients resulting in ill thrift and poor growth of calves.
"Oocysts can be detected in the manure around 21 days after infection"
Signs of coccidiosis are quite deceptive since clinical symptoms of the disease are not detectable in the subclinical stage when most of the damage to the intestinal lining is occurring. A mild fever may occur but in most cases the temperature is normal or subnormal.
The rupture of the cell lining of the intestine during the coccidia's multiplication results in diarrhoea and blood loss. The dark faeces is foul smelling, watery containing blood or mucus. The clinical stage usually lasts 3-7 days towards the end of the 21-28 day parasite cycle and the calves hind legs and tail are soiled with the loose smelly faeces.
"Blood manure contains oocysts which can readily infect other calves"
The calves generally lose their appetite and are depressed and dehydrated and subsequently lose weight. Calves become weak and uncoordinated and may show muscular tremors and convulsions. Irritation of the large intestine and rectum commonly causes excessive straining and in extreme cases the rectum may prolapse.
Should the calves lose large amounts of blood they become anaemic and the gums look white or blue instead of pink.
"Clinical symptoms may last for 3-7 days depending on the severity of the infection"
In acute cases the calves may not be able to stand and die in 1-3 days. Secondary bacterial infections (eg pneumonia) can accentuate the incidence of both morbidity and mortality. During the acute period, secondary complications require supportive therapy (electrolyte fluids and antibiotics) to control secondary infections.
"Destruction of the epithelium lining of the intestine results in diarrhoea, loss of appetite and general emaciation"
There is a general misunderstanding regarding the treatment of coccidiosis due to the subclinical and clinical stages of the disease.
When there are clinical symptoms, the protozoa have gone through their life cycle and the opportunity to control the disease is extremely limited. Alternatively, treatment
prior to the clinical stage and preferably before the subclinical stage prevents production loss and the complications of secondary infections.
"The most effective control of coccidiosis is its prevention"
Treatment after an outbreak is not efficient or cost effective. Through experience outbreaks can be anticipated allowing early intervention with approved and effective coccidiostats.
Continuous treatment during the acute stage is necessary to minimise further outbreaks and limit possible infections.
"Anticoccidial products should be administered at the correct dosage rate for the necessary duration"
In the event of secondary diseases, supportive therapy (electrolyte fluids and antibiotics) under veterinarian supervision may be necessary to minimise calf wastage and further production loss.
"Treatment after an outbreak can be unrewarding and costly"
The most successful method of control and prevention of coccidiosis is the continuous medication with effective coddidiostats in the drinking water or feed (eg ionphore antibiotics such as monensin, lasolacid, narasin or salinomycin).
There are several anticoccidial medications available to prevent and control the disease.
"Prevent and control don't mean the same thing"
If a product has a control label, it will only reduce the severity of a coccidiosis outbreak, whereas products with a prevention label will stop clinical signs from occurring. Some products have the capacity to provide prevention and control. Various products have different dosage rates, duration of use and modes of administration (eg drench, feed or water additive), ie it is important to read the directions.
"It is easier to prevent coccidiosis than treat it"
Where possible the contamination from the oocyst stage in the manure should be avoided. Removing stock from sources of contamination interrupts the life cycle of the parasite and helps control the disease. Since moisture favours the development of the parasite and dryness kills them, practices that reduce moisture decreases parasite contamination. Boggy areas around troughs, dams and feed areas (eg roundbale and grain feeders) should be well gravelled. Areas where stock congregate, overgraze and build up manure deposits should also be avoided.
Coccidiosis is stress related. Changes in the weather and feeding practices particularly with stressful stock husbandry practices (eg branding, dehorning) and weaning can precipitate coccidiosis outbreaks. The first 30 days after weaning is stressful and calves/weaners only consume 0.5-1.5% of their bodyweight in the first 2 weeks of weaning, taking up to 4 weeks to reach full feed intake at 3.0-3.5% of their bodyweight.
"Maximum protection with medications is needed at weaning"
As well as diarrhoea and weight loss, coccidiosis can suppress the immune system. The immune suppression can make the calves more susceptible to other diseases (eg respiratory infections) which further setbacks growth and weight gain. Calves with clinical coccidiosis can be 25kg-30kg lighter than uninfected calves.
"Calves with lower levels of natural immunity are the most at risk"
Mild cases of clinical coccidiosis maybe confused with other diarrhoea problems. Calves with mild coccidiosis only regain normal weight slowly and are often penalised by poor growth and performance.