Weaning – Frequently Asked Questions  

Assuming calf hits appropriate weights, what’s the difference you get weaning at 6 weeks or 8 weeks?

If the rumen is ready for weaning, the age is not so important. If the calf’s rumen is developed enough by the time the calf is six week of age means it will be a step further ahead than if the rumen is ready at eight weeks of age. The calf weaned at six weeks will have two weeks extra supporting itself with the rumen only and so, will be more ready for changes in diet when they come. Furthermore, it will help save on the cost of milk replacer, which takes up a large chunk of the cost rearing calves.

What is the ideal weight for weaning calves?

There is no ideal weaning weight. Although, it is rumoured that the calves must double their birth weight by weaning time, if their rumen is not developed, they are not ready for weaning. If the rumen is developed i.e. calves are consuming at least 1-2kg meal, calves are ready to wean. On systems such as once a day this will be earlier so calves will be lighter than an ad-lib milk feeding system but will still achieve great growth rate. 

What do you mean by ‘sufficiently developed rumen’?

The rumen is inactive when the calf is born, i.e. it cannot function. The pre-weaning period is the time during which the calf uses milk to stay healthy and grow, while they develop their rumen and prepare for life after milk. As the calf grows and increases the consumption of concentrates and forages, the rumen is gradually developing. This development continues post-weaning but calves can be weaned off milk when the rumen is functioning enough to support the requirement for growth and maintenance of health. This is typically a minimum of 1 kg concentrates before gradual weaning begins. In large groups the measurement would be an average estimate per calf. As the actual amount will vary among calves 1.5 – 2.0 kg consumption per calf will ensure all calves will be consuming a minimum of 1 kg of concentrates daily.

Do my calves need to double their birthweight for weaning?

No. The weight of calves at weaning will be somewhat determined by the type of milk feeding system in operation. This is due to the varying rates of rumen development. If rumen development occurs earlier, for example in a once a day feeding system, the calves may not have achieved double their birth weight but will continue to grow and thrive post weaning due to the ability to sustain themselves with their rumen. If a calf is on an ad-lib system, or fed high volumes of milk, they will typically take longer to develop their rumen and so by the time they are ready for weaning, they could be more than double their birth weight.

If my calves are at grass would it be ok if I weaned them earlier?

Typically, rumen development will be a little slower in calves at grass, so later weaning is more common. Luscious spring grass can be attractive for calves, resulting in high consumptions. If the calf is consuming large amounts of grass, they will be slower to eat concentrates than calves reared indoors. Concentrates play a major role in developing the rumen and slower uptake will delay rumen development. Furthermore, as grass is a highly inconsistent feed for calves, they would need at least 1 kg to support the rumen through the changes in its consistency. It can be difficult to get calves to achieve a target consumption of at least 1 kg of meal in luscious grass and so a more gradual weaning can help transition calves.

Should calves still have access to straw when first pit to grass?

If grass is leafy, yes this would be a good option. Grass is a big change for calves and they don’t have a sufficient amount of the right microbes to digest it. If on young leafy grass, offering straw to calves will aid the transition and help satisfy their fibre requirements.

When is the best time to wean?

The best time to wean is when calves are consuming >1kg concentrates for at least 3-4 days consecutively. This is the calves’ way of telling you they have an adequately developed rumen as they are successfully able to but away a substantial amount of feed other than milk. If you are estimating the amount of concentrates each calf is consuming in large groups work it out at an average of >1.5-2kg per calf. Another important point to timing of weaning is to wean at separate times to stressful events, such as turnout, unstable weather, vaccination, etc. Calves will take things in their stride if changes are gradual and all stresses are kept minimal.

Do calves need to be a certain weight by weaning time?

No, calves do not need to be a certain target weight by weaning. If calves have sufficiently developed their rumen, they will continue to grow post weaning. If not, they will likely experience a considerable growth check & possibly illness during/post-weaning, regardless of their weight. Weight gains are a more important target for calves. Calves should easily be able to gain 0.8-1.0 kg liveweight gain per day leading up to weaning and continue this during and post-weaning, regardless of their weight. If they are ready for weaning, they will adjust to life without milk on a gradual weaning programme without so much as a hiccup.