Grazing advice: methods to ensure that your herd health stays in perfect condition

1. Meal Feeding
With Grass Tetany, the surest method of prevention is to feed 2 ½ oz of Cal-Mag per cow per day in meals. 

Problems can arise if some cows refuse meals when sufficient grass becomes available.

When meals are required this method of prevention costs only about 3c per cow per day. Apart from feeding magnesium, most cows should be getting a few kg concentrates until after the breeding season.

Make sure that the level of magnesium in the ration matches your feeding rate when cows go to grass.

Compounders will include different levels of Cal Mag for different feeding rates. Too much magnesium will cause cows to scour and this can be a problem when concentrates have to be increased in bad weather. Check with your compounder.

Most compounders make a ration with high levels of trace elements and also contain sufficient Cal Mag for about 2 kg per day feeding rate and this is the best option for many farms.

In early spring, when cows are on different levels of ration due to varying weather conditions, it can be difficult to ensure the proper level of magnesium through meal feeding so other methods such as water treatment or pasture dusting may also be used.

This is the period when most losses occur due to magnesium deficiency.

2. Pasture Dressing

Spreading 7-10 kg of fine powdered Calcined Magnesite per acre (depending on grazing stocking rate and risk of tetany). It is an effective method of preventing grass tetany if carried out properly.

Where 80 cows would be grazing two acres of spring grass per day, the cost of the material is about 10c per cow per day. It can be spread a few days in advance of grazing, on damp pasture.

A lighter pasture dressing can be very useful as an additional precaution against fatalities, even if other preventative methods are being used, for example, if some cows give up eating meals.

If cows are off meal feeding, pasture dusting is a reliable preventative method.

3. Drinking Water Treatment

There are several soluble magnesium salt products on the market for mixing through drinking water.

Problems may arise in very wet weather if intake of treated water is very low.

Inclusion is usually based on cows drinking 35 litres water per day but this can vary widely.Generally, at best, these supply 20 gm magnesium but can give satisfactory protection if managed carefully, because the magnesium is soluble.

Trace elements are added to some of these products. They can be fed through inline dispensers or trough dispensers.

Some farmers just add the correct amount of product to the water in the troughs.

Powder formulations can be bought and made up, containing magnesium and other minerals.

4. Free choice

Commercial magnesium products are available in buckets. As with any free choice system, this is not as reliable. Buckets are more suitable for suckler cows.

Another free choice system is to mix equal parts by weight of molasses and Calcined Magnesite. The mixture has to be stirred three times daily, this system requires a lot of attention to ensure all animals get their requirements and could not be generally recommended for dairy cows.

Magnesium blocks also require very good management, and are not generally recommended for dairy cows.

Of course, pre-calvers can be neglected in the rush of spring work, which could have serious consequences for later calvers.

In-calf animals must be kept in correct condition and must get pre-calver minerals.

Remember that a cow’s intake drops rapidly in the last few weeks before calving and feeding some concentrate during that period is generally recommended.

After calving, concentrates should be introduced gradually, starting with about 3 kg and increased by 1 kg per day, depending on grass availability. Peak milk supply occurs about six weeks before peak appetite on grass.

Therefore, in order to avoid negative energy and excess condition loss, it is important to continue supplementation until grass intakes are at a satisfactory level.

On the majority of farms, milking cows will require at least 3kg to 4kg of concentrates until sufficient good grass becomes available, and around 2 kg during the breeding season. 

The guideline should be to make optimum use of grass while feeding adequate concentrates to maintain good health and fertility and minimise loss of condition between calving and breeding.

An excellent warning sign of underfeeding can be got from closely monitoring the protein level of milk.

During the first few months of lactation, underfeeding can drop the protein level in milk from around 3.4% to 3%. Keep a regular check on milk protein and adjust concentrates accordingly.

Neglecting nutrition in order to cut costs really must be avoided. Examine all your alternatives. Selling some stock would even be a better alternative.

The aim should be to get as much grass as possible into calved cows and yearling heifers that might be behind target weights.


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