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Nutrition

Course: Spring turnout management | Last Updates: 15th October 2015

But, with some careful feeding and monitoring of cows' condition, farmers can mitigate the risks and maximise yields from grass.

What are the main problems?

The flush of spring grass can cause two main macro-mineral disorders in cattle – staggers and milk fever. Fortunately, staggers – or hypomagnesaemia – is relatively rare these days, as most people understand the risks and take action to prevent it. But when it does occur it can be devastating, with the first signs of a problem often a dead cow.

The disorder is caused by a deficiency in magnesium – the magnesium content of spring grass is particularly low. Cows can't store the mineral in their bodies, and are therefore dependent on their daily dietary intake as a source. The high moisture content and low dietary fibre levels in spring grass also speed up the transit of food, reducing the time available for absorption of essential minerals.

Symptoms, when found early, include jittery, twitchy cows, rapidly progressing to seizures and death within hours. The best way to avoid this is to ensure sufficient magnesium content in the diet, through supplements, either mixed into feed or water sources, a bolus or an application of magnesium to grazed leys. Typically, a 40-litre milking cow needs about 40-50g of magnesium a day. Providing dietary fibre will also help to slow down digestion and improve mineral uptake.

What is milk fever?

A much more common mineral disorder is milk fever, or hypocalcaemia, affecting transition and freshly calved cows. Milk fever is caused when a cow needs to export calcium into her milk, but is unable to source sufficient amounts from her diet or bone reserves. This happens when the diet contains too many positive ions (from sodium and potassium) and too few negative ions (from chloride and sulphur), reducing her ability to mobilise calcium reserves from her bones.

Fast-growing, stemmy grass is high in potassium and low in magnesium and calcium, meaning spring grazing is often associated with a run of milk fever cases. Clinical symptoms include delayed and difficult calving, unsteadiness on the feet, constipation, poor food intake, low temperature, dopiness and an S-shaped bend in the neck. However, clinical cases are just the tip of the iceberg – for every clinical case there are six or seven sub-clinical cases, in which cows may appear normal.

The effects of sub-clinical milk fever are still significant. Calcium is needed for muscular contractions and affects both the digestive system and uterus. Poor gut contractions reduce dry matter intakes, increasing the risk of energy shortfall and displaced abomasums, while poor uterine contraction increases the risk of retained cleansings and uterine infections.

The national average incidence of clinical cases is 6-7%, but ranges from zero to 40% in individual herds. At a cost of up to £200 a case – more in sub-clinical cases – getting on top of milk fever is critical. Many farms now choose to house close-up dry cows. When kept at grass, they should graze only short swards in paddocks with a low potassium index, and be given access to straw or other low potassium forages.

Dietary magnesium is also needed for effective absorption of calcium from the diet, so feeding small amounts of magnesium chloride (80-120g) in feed or water will lower the risk of milk fever. High-risk animals may be given a calcium bolus immediately post-calving, and urine testing can identify potential problems with milk fever before they occur.

What causes a displaced abomasum?

Displaced abomasums are most common in the spring, with about 3% of high yielders affected each year – and up to 10% in some herds. The most dangerous time tends to be in the first six weeks after calving. Milk fever is a common precursor, but other factors include a low dry matter intake with a diet deficient in effective fibre, but full of fermentable carbohydrates.

As the carbohydrates in the diet ferment, they produce gas in the abomasum, floating it into the wrong position. Animals will go off their feed, particularly concentrates; yields will drop and cows will look tucked up and sore. Treatment is costly, at about £250, as it almost always requires surgical intervention. Prevention is always better than cure, and providing a high-fibre buffer feed will improve rumen retention times, helping to keep the abomasum in place.

What is ketosis?

The changeable nature of spring grass, with dry matter content and sugar levels varying on a daily basis, means you can never be quite sure how much energy the cows are consuming. Sub-clinical ketosis – or excessive negative energy balance – is common in cows during their first 60 days of lactation, when a peak demand for energy clashes with insufficient intakes.

To provide milk for the calf, cows instead mobilise fat from body reserves, which are processed in the liver. When too much fat is mobilised, the liver can be overwhelmed and fat builds up, compromising its function, as well as the cow's immunity and fertility.

Clinical ketosis is quite rare, with symptoms including twitchy, nervous cows with reduced yield. However, sub-clinical ketosis, which may go unnoticed, is extremely common, affecting up to 40% of the national herd. It causes significant fertility problems in the following weeks and months. Cows with sub-clinical ketosis will suffer from lower milk yields, with a slow rise to peak, and will be more prone to infections such as endometritis, which again impact on fertility.

Producers should consider buffer feeding high-yielding cows grazing spring grass, and regularly review their ration with the help of a nutritionist. A loss of one body condition score point between calving and peak yield suggests serious problems exist. Better still, basic, inexpensive and regular metabolic profiling can help to identify herd issues early on, before the economic impact is felt. This is especially pertinent for seasonally calving herds.

What linked conditions should you look for?

It is clear that many metabolic diseases caused by incorrect nutrition can lead to other, linked conditions. Metritis and endometritis are no different. While they can be triggered by insufficient micro-nutrients in the diet, particularly antioxidants such as selenium, vitamin E and beta-carotene, infections can also result from retained cleansings, in turn caused by milk fever or sub-clinical ketosis.

Roughly 8-15% of the national herd is affected by retained cleansings each year, at a cost of about £85 a case. When the afterbirth fails to detach within 24 hours of birth, animals should be marked and checked 21 days after calving, to see if they are suffering from endometritis. Some animals will develop the more serious condition, metritis, and should receive immediate veterinary treatment.

At-risk stock, particularly older cows or those carrying twins, should receive plenty of calcium after calving, and may benefit from an injection of oxytocin at calving to help the uterus contract.

Golden rules

  • Draw up and implement a nutrition strategy with your consultant, to prevent negative energy issues and macro-mineral disorders around turnout
  • Always feed sufficient functional fibre to boost rumen fill and function
  • Make use of routine blood and urine testing to identify sub-clinical problems before the economic damage is done
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