Good rumen development is the key factor in determining whether your calves will cope with weaning off milk well without any growth setbacks. When calves are born the rumen is small and inactive, the abomasum is the main stomach being used at this time. As calves begin eating meal, roughage and water the rumen begins to develop. The rumen microorganisms grow rapidly when fed a high-quality meal and they produce volatile fatty acids, butyrate and propionate which help develop the rumen papillae.
For a visual comparison of rumen development under different feeding regimes, see the photo series published by Penn State Extension. The pictures show the inside rumen of some six-week-old calves and their diets since birth. Notice how the rumen papillae are far more developed where the calf was fed a high-protein meal.
Fresh water is equally important. Rumen microbes require water to ferment feed effectively, making unrestricted access to clean water essential from an early age matters as much as the milk they are fed.
So, management prior to weaning is the key to setting them up for success.
Instead of weaning based on weight or age, calves should be weaned depending on how much calf starter/meal they are consume as this gives the best indicator as to how well rumen developes internally. We recommend calves should be consuming an average of 1.5-2kg meal per day for three consecutive days before weaning.
If meal is not fed to calves, eventually the rumen will develop if they are fed forage alongside the milk; it is just very important to recognise the rumen papillae will take far longer to develop. In this situation, calves should be weaned much later and taken off milk more gradually with their weight gains carefully monitored.
One common mistake after weaning is removing the calf meal too early. Although calves are no longer receiving milk, their rumens are still developing, and their nutrient requirements remain high.
Continuing to feed a quality meal for several weeks after weaning helps maintain growth rates and provides a consistent source of energy and protein while calves adapt to increasing amounts of pasture and forage. Abrupt changes in diet can reduce growth performance and increase weaning stress so if calves are being moved to a runoff we also recommend continuing to feed meal through this transition at least for a couple of weeks once they have arrived.
As well as meal, young dairy calves require a top-quality pasture to gain weight well. The grass ideally should be easy to eat, not hard and fibrous. Equally too much wet weight can quickly fill a young animals rumen capacity so in a wet season we also need to account for this by supplementing for longer.
Weaning is also a useful time to review your youngstock health plan especially regarding trace elements. Deficiencies can negatively affect growth, immunity and overall health.
We recommend both monitoring and proactively supplementing with:
Requirements vary depending on farm location, soil type and feeding system. Blood testing can help identify deficiencies and determine whether supplementation is required. If you already know your farm’s history well, at this stage, you may simply need to ensure the correct trace minerals are given. Prolaject™ B12 is usually the first one we recommend supplementing with around weaning time and this can be very useful to ensure the rumen bugs are functioning as efficiently as possible.
As calves spend more time grazing, the risk of internal parasite challenge increases both from gut worms, lungworm and coccidiosis. Youngstock have limited immunity to parasites and can experience reduced growth rates before obvious clinical signs are noticed.
Faecal egg count monitoring can be very helpful alongside good pasture management and good feeding. Strategic drenching will still likely need to be used but please work with your vet to develop the best plan for your farm especially taking note to avoid a developing resistance problem.
✓ Calves are eating 1.5-2kg of calf meal before weaning.
✓ Clean water is available at all times.
✓ A quality weaner ration is continued after milk is removed.
✓ Growth rates are monitored by regular weighing through and after weaning.
✓ Trace element status is assessed and supplemented if required.
✓ A parasite control plan is in place before calves begin grazing larger pasture areas.
Prolaject B12 2000 Plus Selenium is registered pursuant to ACVM No. A006903.
If you’re preparing to wean calves this season, contact your local Vetlife clinic for tailored advice on nutrition, growth monitoring, trace elements and parasite management. Small decisions now can make a big difference to lifetime performance.
Related articles:
Monitoring Your Heifers Post Weaning
Learn why monthly weighing matters, how to identify calves falling behind target weights, and the management steps that protect future milk production.
Sustainable Drench Use in Dairy Heifers
How to use faecal egg counting, targeted selective treatment and pasture management to maintain parasite control while reducing drench resistance.
Trace Element Monitoring
Find out which trace elements matter most for growth and immunity, when to test, and how to build an effective supplementation programme.
