Top tips on how to manage dry cows at grass

However, the benefits including savings on forage and straw bedding must be weighed up against the risk of harming future productivity from potential milk fever cases and excess condition gain when dry cows are grazing good quality grass.

Grass is typically high in calcium and can also be high in potassium (K), especially if the ground has had slurry or K fertiliser applied. The high K reduces magnesium absorption, with magnesium being important for the control of hormonal mechanisms which stimulate the release of calcium from bones at the start of lactation. Too much calcium in the diet in the run up to calving can make the cow’s calcium release mechanism 'lazy' and less able to mobilise calcium reserves from bones.

A dry cow mineral supplement with very low calcium (<2%) and high magnesium (around 20% depending on feed rate) is recommended during the dry period. However, calcium may need to be added to dry cow rations when using anionic salts such as magnesium chloride.

While clinical signs of milk fever may not be evident, subclinical cases can still increase the risk of developing other transition diseases such as retained cleansings, metritis, displaced abomasum, ketosis, and mastitis.

Subclinical milk fever can be diagnosed through blood testing cows within 24 hours of calving. A blood calcium level below 2mmol/litre is classed as a subclinical milk fever case and below 1mmol/litre, a clinical case.

Transition cow disease targets

Health performance indicator Target level

Milk fever <5%

Retained placenta (>12 hours after calving) <5%

Metritis

% infected after 21 days <10%

Endometritis

% infected after 21 days <10%

Ketosis <5% in first 3 weeks

Displaced abomasum <3%

Culled in 1st 60 days <3%

Lorna MacPherson

The milk fever risk from grass can be reduced with a high stocking density or keeping dry cows on bare grass paddocks. As a guide aim for around 3-4 cows/acre with a grass height of 4cm. This is not always easy to achieve when grass growth rates are high.

When restricting grass intake, cows should be supplemented with low quality forages, either straw or hay or mature grass silage to maximise appetite and rumen fill but avoid putting on condition. Recommended supplementary forage type and intake will vary depending on its dry matter and feed value and it is best to seek nutritional advice.

Cows with unrestricted access to good quality grass will be greatly exceeding their energy requirements, leading to condition gain and fat deposition around the internal organs, predisposing them to greater risk of fatty liver and ketosis in early lactation. Cows should be dried off at a condition score of 2.5 to 3 and ideally no more than 3.25, which should be maintained until calving.

During periods of wet weather, the low dry matter in grass can greatly reduce dry matter intake and rumen fill if relying on grass as the main source of forage.Poor rumen fill and a reduced appetite pre-calving will lead to poorer appetite post-calving and increase the risk of a displaced abomasum shortly after calving.

If cows are struggling with a poor transition into the milking herd and health issues at calving, it is advisable to house them three weeks before calving to have control over their dry matter intake and ensure adequate nutrition during this crucial period.

Tips for managing dry cows at grass:

• Try to restrict intake of fresh grass and also provide low quality forage to maximise rumen fill but avoid putting on condition.

• Keep an eye on body condition score to ensure dry cows are not gaining unnecessary condition in the early part of the dry period.

• Graze dry cows on old, more mature grass that has not been heavily fertilised/slurried to limit potassium intake.

• Provide a suitable dry cow mineral supplement which is low in calcium and high in magnesium.

• If cases of milk fever or other related conditions (retained placenta) increase at grass, bring cows inside three weeks before calving and feed a dry cow ration formulated for milk fever control with appropriate mineral supplementation to suit the forage being fed.