Udder development and milk production is commonly seen in non-pregnant and pregnant dairy heifers on long haul voyages. Sometimes whole consignments of heifers that are less than 7 months pregnant can undergo synchronised rapid udder development over a few days to a week beginning after a week or more at sea. Milk may leak from teats of engorged udders.
The cause is unknown but appears to be associated with pellet feeding at sea. If the diet of pellets is replaced with chaff or hay, the problem subsides, but resumes when pellets are reintroduced. When affected cattle are unloaded at destination (and pellets are no longer fed) they return to normal usually within a day or two. Jerseys appear more predisposed than Friesians and it is more common in pregnant than non-pregnant heifers.
Premature lactation has potentially serious negative consequences. Some animals may develop mastitis which can be severe, difficult to treat and result in permanently reduced milk production from infected quarters. There have been disputes about the pregnancy status of affected animals at destination - buyers were suspicious the animals may have aborted on ship. There is also concern in pregnant heifers that colostrum will have leaked out and be unavailable to feed and provide immunity to the calf when it is born.
Udders will be distended with spraying or leaking of milk. After washing, white milk can be seen clearly on the decks in pens. Cases of mastitis may be an initial indicator of premature lactation. Widespread udder development can develop quickly in a large number of animals in just a few days.
The differential diagnosis is prepartum udder oedema associated with normal calving or late term abortion. With prepartum udder oedema, milk does not leak, the swelling from the subcutaneous oedema is predominantly anterior to the udder, and mammary development is usually mild to moderate at worst.
If mammary development is observed, replace some or all of the pelleted ration with chaff or hay for affected animals to try to prevent onset of lactation.
In consignments of dairy heifers it is recommended that routine pen inspections include scanning of the udders, particularly in higher risk animals (Jersey and/or pregnant). Ensure plenty of chaff is on board to replace or reduce pellet feeding if necessary. Ensure plenty of sawdust is available to keep decks as dry for as long as possible to prevent mastitis.
The use of teat sealants such as Teatseal™ may be attempted to prevent mastitis. However, administration may be difficult in the assembly depot because there may not be a suitable crush facility, and the teat canals of heifers may not be sufficiently patent for proper insertion. Also, if an animal does develop premature lactation milk flow will wash out the sealant and the animal may become susceptible to mastitis anyway.