Phosphorous Deficiency – What to watch out for!

The dry weather we have been having with easterly and north-easterly winds has given rise to a soil moisture deficit, according to Met Eireann soil moisture deficit of 13-33mm have been established. With more showery weather due this will correct the deficit with time and grass growth will recover.

This rainfall deficit has given rise to purple tinging of leaves in the grazing swards which is indicative of ‘Phosphorous’ deficiency in the plant irrespective of the soil index but more prominent in fields of index 1 and 2 and requiring lime. The requirement of phosphorous in the diet of the dairy cow at this stage of lactation is 0.4% per kg DM. Under these circumstances, phosphorous has dropped in grazing sward analysis from 0.4% to 0.27% per kg DM.

DAFM Regional Veterinary Laboratories have reported in April phosphorous being an issue of 73 bovine bloods tested 47% were low. Dairy cows and other stock will be seen to be licking and consuming stones and chewings pipes where phosphorous intakes are not meeting requirements. Phosphorous has a role in energy production, muscle contraction and is excreted from the saliva when the cow chews the cud, therefore, buffering the rumen and optimizing microbial growth critical for milk protein. She can become anorexic which will lead to reduced DMI (Dry Matter Intake) at this point in time with peak milk yield and the breeding season in full swing needs to be avoided.

In these circumstances with soil moisture deficit, two other macro minerals will also be low in availability and that’s calcium and magnesium, therefore check that your compound feed have calcium included at 1.4%/kg as fed. Depending on grass growth where buffer feeding is required top dress with 70-100 grams of a post-calving mineral.


Over the last two weeks on visiting farms on average, 5% of dairy cows have dirty backsides indicative of high worm levels for these individuals. If herd worming is planned for by the end of the month or in June it would be worth treating these individuals immediately to optimize nutrient absorption, production and their health.


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