Clinical and subclinical coccidiosis in calves can result in significant financial losses, as a result of poor health, ill thrift, lost condition and weight, and severe cases death.
Even under rigorous hygiene regimes, calves may be exposed to the coccidiosis causing protozoan parasites soon after birth. This is because the coccidia oocytes shed by infected calves in dung can remain viable for up to 2 years under suitable conditions. Coccidia have a short lifecycle, and their spores become infective within a few days of being shed, resulting in rapid increases of infective spores in sheds used to rear consecutive batches of calves.
Clinical cases are easy to identify, but it has been estimated that only 5-10% of infected animals show clinical signs of coccidiosis. Since subclinical coccidial infections do not exhibit signs of the disease, calves could be infected without calf rearers realising. Subclinical coccidiosis can be the period before the appearance of typical signs of the disease, or when infected animals do not show signs of infection.
The parasites damage gut walls of infected calves, resulting in reduced absorption, bleeding and scouring. Other symptoms include loss of appetite, ill thrift, weight loss and dehydration. If calves are not treated then chronic cases can arise, due to continual infection overwhelming calves abilities to overcome the disease.
There are several methods of controlling coccidial parasites, which can be administered either via milk, milk replacers or in calf feeds. Most commercial brands of calf milk replacers contain coccidiostats, such as decoquinate, which disrupt the parasites’ reproductive lifecycles, lowering the challenge, and allowing calves’ immune systems to develop resistance to the parasites.
Ionophores, such as monensin sodium and lasalocid sodium, are another of the groups of products used as coccidiostats, as they disrupt the flow of ions into and out of the coccidial cells, resulting in their death. Most commercial starter calf meals contain ionophores. However, full protection may not be achieved if eating less than 1kg of meal as the ionophores have a different mode of action from those in milk replacers.
Therefore, ionophores should be added to milk or milk replacers to provide some protection from day one. This can be achieved with milk by using a product specifically designed for this purpose to ensure the calf is effectively protected till they are eating approximately 1kg of meal, if the ionophores are the primary medication for the control of coccidiosis.
Whatever the preferred method of coccidiosis control, well fed calves have much greater abilities to mount effective immune responses against coccidia than ones getting just enough for their maintenance needs. Another key factor in controlling coccidiosis is good housing, use of effective detergents, and good management and feeding.
As featured in NZ Dairy Farmer