Reducing milk fever at grass

Posted by rebecca on Apr 11, 2017, 4:05 PM

Everyone involved with dairy cows is only too aware of the high risks of milk fever and metabolic disorders arising from an excess of calcium in the dry cow diet. And it’s not just a problem when grazing.
Consider this. The target calcium level in a dry cow diet is 30g/day. The average calcium content of UK grass silage is 8-10g/KgDM, so if a dry cow eats 12kg of forage DM per day, that’s up to 120g of calcium per day. This excessive level of calcium will prevent the cow from mobilising supplies from her bones right when she needs it, at the point of calving.
The problem can be exaggerated at grazing. Heavily fertilised grass is high in potassium which creates an alkaline effect in the blood, causing the blood pH to rise and reducing bone calcium mobilisation.
The principle behind feeding low calcium diets is to encourage the cow to use her natural defence system for preventing hypocalcaemia. There is a massive increase in calcium demand at the onset of lactation, with calcium requirements doubling in the 2-3 days immediately pre-calving. A cow giving 35 litres requires approximately 1.2g of calcium per litre. This
means she has to produce 42g of calcium per day. The exchangeable pool of available
calcium is approximately 12g, so if this is not replenished this pool of calcium will be
exhausted within 10 hours, hence the need for her to mobilise bone calcium quickly at
the time when she needs it.
Cows at a higher risk of milk fever include:
 High yielders
 Jerseys, due to the higher milk quality
 Older cows, as their ability to mobilise calcium is diminished.
What we can do to reduce the risk?
Speak to your Massey nutritionist about having a forage mineral test. This will
flag up any risk-factors such as silages high in potassium. A bespoke dry cow mineral pack can then be formulated. For example, dietary phosphorous levels can be increased to bind excess calcium in calcium-rich silages.
Feed sufficient magnesium. 40g per day is the requirement to allow the magnesium dependant enzymes to regulate calcium homeostasis. This can be supplied in 2kg of Massey dry cow rolls or in our dry cow minerals. Adding Mag-chloride flakes to water troughs is a widely practised way of getting magnesium into cows but it does affect water palatability and you can’t be certain about intakes.
Feed anionic salts in the TMR. Again, these can reduce palatability but if intakes are correct then they are effective.
However, these approaches may not always be practical-particularly at grazing, so consider using a calcium binder.
Feeding a calcium binder in the two weeks prior to calving reduces the uptake of dietary calcium such as that in grazed grass and in silage. The principle is straightforward. It binds the calcium in the small intestine making it less available for absorption. This primes the hormonal system to mobilise the bone reserves of calcium at the time of calving.
It can be fed in a TMR down the barrier. The controlled trials show an effectiveness of 100% under practical arming conditions and there have been no negative side-effects associated with feeding it. More recently, its effectiveness has been backed up by trials done in association with Harper Adams University.
For more information on our dry cow products contact your feed specialist or speak to Dawn Jones at Holmes Chapel.

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