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  • Writer's picturePat Poletti

Walking the Tightrope of Milk Fever

Updated: Jun 22, 2021

“Every day begins with an act of courage and hope: getting out of bed” quipped US writer Mason Cooley. He may have had a milk fever problem. Milk fever has been recognised as a specific disease of dairy cows for over 200 years – and it’s still a serious problem. The science is difficult and contradictory. Ask Mr Google what he thinks and you’ll get a run down on low blood calcium, parathyroid hormone and vitamin D. Include DairyNZ in the search and you’ll get condition score, DCADs and magnesium (and lots of it).

Down cow rates vary widely. The DairyNZ target is less than 1%. Most farms are around 2-5% and a significant number of others can be much higher – 20% and in one case currently under study – 40%. At the 2%-5% rate nearly every cow in the herd will be affected. Apart from the clinical cow, the side effects of milk fever (calving problems, retained membranes, infected uterus, slow return to first heat, increased risk of mastitis and ketosis) are immense.

The most minor effect and perhaps the most important will be simply reduced appetite. If we bear in mind that for a 450kg cow the difference between 1.8kg milk solids and 2.0kg is only 1.4kg of dry matter (11ME) and, that milk fever is not just confined to calving time but can occur at any time during lactation, we should be pretty interested in how milk fever affects our herd throughout the year even if the clinical syndrome is not that dramatic.

Anionic salts and copious magnesium only deal with the risk posed by low dietary magnesium and high potassium. There are also risks such as excessive phosphorus, very low calcium to phosphorus ratio, very high and very low dry period calcium as well as a few intriguing issues such as thyroid gland changes after winter feeding of brassica crops or chronic iodine deficiency.

If you don’t drench, the more that you have to supplement via the water, feed and dusting, the greater the risk that supplementation will fail e.g. if you run a very high pasture potassium you will need a lot of magnesium. The more magnesium you need the more the cows will seek to avoid it. As their ability to avoid it increases, the greater the risk of disease.

Reducing the reasons for a lot of supplement then reduces the supplementation requirement and mitigates risk. As this risk is commonly derived from fertiliser policy the ability to adjust fertiliser practices presents a real mechanism to manage milk fever risk and reduce the cost of mineral supplements.

Cows are on a tight schedule. Not only on a tight seasonal schedule to calve, cycle, and get in-calf, but a tight daily schedule to eat, sleep, walk and be milked. Everything we can do to assist this annual and daily schedule is critical. Managing milk fever risk at all stages of the season gives cows the critical time they need. And for the rest of us makes it a little easier to get out of bed in the morning.

#MilkFever #Downcows #Highdietarypotassium #Lowdietarymagnesium #lowcalciumtophosphorousratio #Fertiliserpractice

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