THERE are some 'added extras' in caring for calves over winter.

Bianca Theeruth, Cargill's calf and heifer specialist, said as temperatures fall, calves need extra energy for maintenance.

"We need to feed more to avoid this energy being diverted from their growth requirements," she said.

The temperature range – or thermoneutral zone – for calves is typically between 10°C and 25°C. Within this, the calf will generally maintain its body temperature and requires no additional energy to keep warm.

"But this temperature range varies with the age of the animal, and in winter, we are particularly concerned about the lower end; the lower critical temperature," said Ms Theeruth.

"For calves under three weeks old, the lower critical temperature is between 10° to 15°C. Below this, the calf will use its energy reserves to maintain a core body temperature of 38°C to 39°C, diverting it away from growth.

"For calves more than three weeks old, the lower critical temperature is between 5°C to 10°C, due to its more advanced rumen development that generates heat, its higher energy starter feed intake and more internal fat stores."

If extra energy isn’t supplied, calves 'burn' body fat reserves and then muscle tissue. This causes weight loss and depresses the immune system.

Ms Theeruth said: "As a rule of thumb, for every degree the temperature drops below the calf’s lower critical temperature, the energy required for maintenance increases by one per cent.

"It is important that farmers recognise this and adapt the calves’ diets so they don’t run short of energy for growth. Nutrition is the first line of defence against the cold."

In the first three weeks, when starter feed intakes are minimal, the extra energy must come from increasing milk or milk replacer.

Ms Theeruth outlined a few routes farmers can take to increase energy intakes for young calves:

n increase calf milk replacer by 100g per calf per day split between feeds. No more than 900g per day of calf milk replacer should be fed;

n feed a 'high' 20 per cent fat milk replacer; and

n increase the volume of liquid, say from five to six litres per calf per day, across two feeds.

A third feed could also be introduced with a maximum of 900g of powder in six litres of mixed milk per calf per day, so split the total concentration and volume into three feeds instead of two. But bear in mind that this may hinder starter feed intake, which can delay rumen development.

She said management is equally important. "Milk should be fed at or slightly above body temperature and a texturised, coarse muesli type starter feed will encourage intakes. And calves need fresh, clean water from day one."

Calf accommodation is crucial. In winter, poorly ventilated and draughty accommodation will create problems. Moving air and fresh air are needed as much in winter as summer.

Dry bedding is one of the most important factors. A deep, dry straw bed will provide insulation; the calf will create a nest effect. Calf jackets for young or sick calves help retain body heat.

"Keeping calves warm, well-fed and comfortable will pay dividends," said Ms Theeruth.