Two years ago SRUC Veterinary Services investigated a number of cases of pica in grazing dairy cows in the South-west of Scotland. This condition was most commonly seen in spring block- calving, New Zealand style grazing herds during the month of May in 2020.

Pica is a condition where cows appear to eat or lick things in their environment that have no nutritional value. For example, in these reported cases cows were observed to be eagerly eating or licking soil and stones and even trying to rip up astroturf on cow tracks. However no other symptoms were seen and cows appeared healthy.

There are a few theories of what causes pica but the main one is thought to be a deficiency of phosphorus (P), although salt deficiency and lack of fibre in the diet have also been implicated, as sodium is important for the absorption of most major minerals.

Blood sampling some cows from the affected herds consistently showed low phosphate levels and this was sometimes accompanied by marginal magnesium status.

It is thought that cows are more at risk when there has been prolonged dry weather in conjunction with very low overnight temperatures, leading to very low phosphate uptake by the grass. Phosphate is not very mobile in the soil, and cold soil conditions can exacerbate poor uptake, resulting in P deficiency in many crops.

The risk of pica appears to be higher in herds maximising the use of grass and has also been linked to low magnesium intake or acidosis, with SARA (sub-acute ruminal acidosis) being a well-known risk in cows on lush spring grass.

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With this in mind, as turnout approaches it is worth reviewing mineral supplementation to grazing cows to ensure that requirements are met. The need for increased magnesium supplementation when lactating cows are at grass to prevent staggers is well known and many feed companies increase the level of magnesium in their summer cakes as a safeguard.

However, P supplementation is not often on the radar and its inclusion in dairy minerals has been gradually reduced over the years due to concerns around P excretion and its environmental impact on water courses.

In addition, P inclusion in a mineral is very costly, currently around £40 per 1%. As many low input, extensively grazed herds just rely on mineralised cake to supplement the grass, it may be worth checking with your supplier whether P is added to the cake.

The following tips may help reduce the risk of P deficiency this spring:

• Analyse fresh grass for mineral content. This will also indicate if there are antagonists present that might reduce P absorption from the gut and take advice on supplementation from a nutritionist.

• Ensure sodium requirements are met and if unsure provide salt licks (if not already feeding a mineral/block that contains sodium).

• Provide added P in the drinking water or from a high P mineralised bucket over the risk period.

• If grass availability is limited, buffer feeding with silage may help, slowing throughput of grass and silage through the gut, increasing time available for P absorption.

• As pica can be due to reduced dry matter intake from poor availability of grass, increasing cake feeding by 2kg/day will help minimise any drop in milk yield, which may also increase P intake from cake if added.

Article reproduced from the Farm Advisory Service