Protecting youngstock from Mycobacterium avium subspecies paratuberculosis (MAP), spread from an infected animals dung, is critical to preventing the spread of Johne's disease.Although the primary objective of contract rearing will not be to protect youngstock from Johne's disease, it could be used an effective management practice to prevent the spread. This could be used in herds that are known to be infected with Johne's disease or for which the infection status is unknown.
Contract rearingContract rearing is an agreement between a dairy farmer and another farmer (usually a dry stock farmer) to rear his replacements for a set period of time. This type of arrangement offers many benefits to both the farmer and rearer; these include:
- Increased land area for milking cows;
- Allows farmer to increase cow numbers;
- Reduces the need for housing facilities;
- Frees up time to complete other jobs;
- Increase income for rearer;
- Steady cashflow for rearer.
Johne’s disease spreadProtecting calves against exposure to MAP – the bacteria that causes Johne’s disease – is an essential control measure, according to AHI. MAP is typically spread from contaminated dung. The spreading of Johne’s disease from dairy cows typically occurs after the second calving or later, and very rarely before the first calving - but it can still happen. Preventing contact between young calves and other cattle is one of your best lines of defence. Calves will gradually acquire some age-related resistance against infection. So risk mitigation of young calves is more important during the first months, and becomes less critical as the animal’s age attains and exceeds 12 months. This is where AHI suggested that contract rearing could be a useful tool in preventing the spread of MAP.
Risk of contract rearingIt is important to be aware of the risk of the potential exposure to Johne’s disease on the contract rearing farm.
If your herd has a known status of having Johne's infection, moving youngstock off the farm may help in preventing it spreading to them.But, if your herd does not have an issue with Johne's and the calves are moved off farm onto a farm that does or may have, this could lead to the calves becoming infected. Grazing your replacements should be arranged so that there is an interval between adult grazing or spreading slurry. Preferably, an interval of 12 months is advised, but if that is not attainable then the longer the better - before the calves graze the paddock. The sharing of pastures and sheds with heifers from other farms is not advised and should be avoided, as it carries risk in terms of biosecurity and Johne's disease.