So how do you best approach this important developmental change?
Fonterra Senior Veterinary Manager Michael Shallcrass and AgResearch Senior Scientist, Animal Nutrition and Physiology, Dr Ajmal Khan provide tips and advice for weaning as part of NZAgbiz's Calf Rearing Answered video series.
In the series, Ajmal emphasises the benefits of feeding calves on a high milk allowance system for their first two months.
"Research during the past decade clearly indicates that we should be feeding higher milk allowance to calves for the first two months. We should not compromise the growth and development of their critical organs - including gastrointestinal tract, the gut of the cow, the mammary gland - so higher milk feeding is critical to not only promote the growth of the animal but also their long-term performance," Ajmal says.
Michael agrees, while acknowledging this approach will mean calves need to be weaned more gradually than those on low milk feeding systems, due to slower development of the rumen - the part of the stomach where solid feed is broken down so nutrients can be absorbed.
"In a high milk feeding system, the calves are getting a lot of their nutrition from milk, they will grow really well - but that comes at the cost of rumen development. So the more milk the calves get the slower their rumen develops," he says. "Until the rumen is fully developed the calves aren't going to be able to meet their entire nutritional demands through solid food alone so if you are weaning calves off milk that didn't have a fully developed rumen you are going to see a significant growth check and that's going to have follow on consequences later in their lives."
"From the calf's perspective, a high milk system with gradual delayed weaning is going to result in the best overall outcome for growth and for productivity into the future," says Michael.
Ajmal advises that calves reared on a high milk allowance should be weaned using a 'step-down' approach which will enable the rumen time to develop and help maintain the initial gains achieved on the high milk diet. The step-down weaning procedure sees the milk offered to calves reduced by 20-25% every four to five days - meaning calves adjust by consuming increased amounts of solid feed - and sees weaning take around three weeks to complete.
"You need to wean the calves more carefully and more gradually over three to four weeks. If you do that, you have a very good heifer with a good rumen development, with a good mammary gland development and with a good intestinal tract, for their life," he says.
Other things to consider when weaning:
- Also avoid major changes to the calves' environment. For instance, weaning should happen separately from transport or even moving to another paddock.
- Weigh a sample of calves to monitor target growth rates before making a weaning or management decision. Weigh bands are a useful tool to approximate calf weights.
- Make sure shelter, water, and hard feed are easily accessible post weaning.
Check out the NZAgbiz Calf Rearing Answered video series for more information and advice.