SPECIAL REPORT
Combating milk fever with diet changes Adjusting feed can alter the pH of your affected cow’s blood, explains Dr Jim Gibbs. Anne Lee reports.
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f milk fever is an issue there are two or three more important factors you should look to before going down the, often expensive, route of using anionic solutions and treating it as a dietary cation anion difference (DCAD) problem. Lincoln University senior lecturer and veterinary scientist Dr Jim Gibbs explains that DCAD refers to the difference between the positive cations and negative anions in the feed. By altering the feed so the difference is slightly negative it’s possible to alter the pH of the animal’s blood which in turn helps the natural parathyroid hormone system to pull calcium out of the bones – necessary post calving when the cow begins lactating and there’s a huge increase in the need for calcium. Managing blood pH to reduce hypocalcemia (milk fever) using feed can be effective in total mixed ration (TMR) diets but in New Zealand’s pasturebased system it’s virtually impossible. Overseas studies show the best way to control 70
DCAD is to limit potassium (K+) at 1% of drymatter (DM) and sodium (Na²+) at 0.1%. “That’s impossible for us in our pasture-based system. Our grass often has K levels above 3%DM and can have Na levels at 1% - so we have a lot of positive cations to contend with that TMR systems don’t have.” “The only way we’re going to get DCAD at the slightly negative level is to feed something with a lot of negatives and all we have available in our feeds are chlorine (Cl¯), phosphorous (P³¯) and sulphur (S²¯). “You can’t feed a lot of these – or certainly not the amount that would be needed to offset the K and Na without causing other major health problems or worse. “People do turn to anionic salts but you have to feed a lot of them – and they’re expensive – but it’s still almost impossible to get around the amount of K in the grass so to do it properly you really need to be feeding them what amounts to a total mixed ration for the springer mob for up to a couple of weeks. “To be frank - even if you could get it completely right the relative significance of DCAD in preventing milk fever here is several steps down the list.
“Get cows off beet 10 days before calving and manage their feed allocation, especially their access to grass because it’s high in K.”
Dairy Exporter | www.nzfarmlife.co.nz | August 2021
