Franklin Vets Blog

Down Cows – Low Phosphorus

July 23, 2019

There are several different reasons for a cow to be down. This can range from metabolic (milk fever, low magnesium, ketosis, acidosis), to an injury e.g. dislocated hip, or nerve damage from bulling injuries. Other issues can include mastitis, metritis (infection of the uterus), or calving paralysis.

It is good to be able to identify a ‘down cow’ and have a plan in place for how you will approach treatment, nursing and aftercare of her. This article will focus on metabolic issue that is not well known about but is becoming more common in New Zealand dairy cattle, the topic of hypophosphatemia (low phosphorus) in the down cow.

First of all, what is phosphorus?

It is a chemical in the body that has important biological functions such as a buffer for acid-base balance, helps with the production of energy, muscle contractions and is a major component of bone. It is excreted in saliva when a cow chews her cud, where it helps to buffer the rumen and also increase growth of the rumen microbes important for digestion. It is also lost in urine. Normal phosphorous levels of a dairy cow are 1.29-2.77mmol/L.

When will you see low phosphorus?dairy cows feeding

Most commonly it occurs around calving. This is because there is a sudden increased demand for phosphorus in the early stages of lactation and colostrum production. Other times can be when there is a decrease in feed intake. So, any cow that is anorexic/off her feed e.g. sick cows, metritis cows, ketosis can lead to a decrease in feed and a decrease in phosphorus uptake. Other animals that may be at risk are high yielding, older cows (phosphorus decreases with age) and animals that are consuming a low phosphorus crop such as fodder beet.

On the other hand, there is also the risk of too much phosphorus. This can occur when animals are being fed a diet too high in phosphorus e.g. PKE, distillers’ grain, or maize gluten. Too much phosphorus can interfere with vitamin D production which is essential for calcium absorption from the diet. This type of feed should be limited to less than 30% of the diet for 2-3 weeks in the transition period.

So, what are the signs of low phosphorus?

Animals can show a number of signs. Classically a cow will present as ‘down’. She may look like what is called a ‘crawler cow’, where she is unable to get up fully and drags herself across the ground in a low crawl. She may be anorexic and have muscle weakness. She may present like a milk fever cow. Other signs of more severe deficiency include red water.

How do we diagnose and treat low phosphorus?

The easiest way to diagnose low phosphorus is through a simple blood test. Although phosphorus in the blood is not extremely accurate, due to other body compartments storing phosphorous, it still is the best available diagnostic tool. Cows that are low phosphorus also tend to be experiencing milk fever. Generally treating milk fever will spontaneously resolve low phosphorus due to the complex chemical roles of these different elements. Calcium helps to correct gut motility, therefore allowing dietary absorption of phosphorus to resume. If a cow fails to get up after treatment for milk fever this may be due to phosphorus not being fully corrected, or other issues such as an injury. You should seek veterinary advice. calcopromag for milk fever

This issue may become more common in New Zealand as we move towards decreasing environmental impacts. Cattle normally have adequate phosphorus intake due to high phosphorus fertilizers being used, but as this changes, so will the amount of available phosphorus. There is also a trend towards the use of lower phosphorus crops being fed to cattle.

For further information please contact your local Franklin Vets clinic.

Download our handy info sheet on low phosphorus

Dr Melissa Kane BVSc (Hons)