The hidden cost of milk fever
Milk fever is a sudden fall in the amount of calcium available in the blood. It commonly occurs within a few hours of calving due to the demands of milk production.
Cows become more susceptible as they age and have a reduced capacity for mobilising calcium from their bones.
Clinical vs subclinical
Subclinical milk fever can affect 40% of cows calving in dairy herds, compared to 2-5%(1,2) for clinical milk fever. That means the majority of cows affected are the ones you can’t see.
The physiological effects of low calcium
Because of calcium’s role in muscle function, telltale signs of milk fever include trembling, weak, staggery movements and inability to stand (down cow). Digestive, respiratory, circulatory and milk producing processes are also affected by low calcium. All of this can pave the way to an array of other serious disorders.
Milk fever as a gateway disease
Milk fever is considered a gateway disease, meaning it can predispose the cow to other conditions, such as ketosis, mastitis and endometritis.
For example, reduced feed intake associated with milk fever leads to mobilisation of body fat to supply energy resulting in ketosis. Even subclinical milk fever reduces muscle contraction to the point that closure of the teat sphincter is affected, increasing risk of mastitis. Milk fever can also impair immunity(2) making the cow more susceptible to infectious diseases like endometritis.
Magnesium’s role in prevention.
Hypomagnesaemia results from low magnesium intakes or absorption. Clinical hypomagnesaemia (grass staggers) is a condition requiring urgent attention. Magnesium is also important for maintaining the balance of calcium; low magnesium increases the risk of milk fever and is why it often plays a part in a prevention strategy.
- New Zealand Veterinary Journal 49(2), 60-67, 2001
- The Veterinary Journal 176 (2008) 50–57